This manual is designed to provide the serviceman with complete information on the operation, construction and maintenance of the 1955 Chevrolet All-Weather Air Conditioning System. A brief discussion on fundamental principles of refrigeration is also presented herein to enable those unfamiliar with refrigeration systems to better understand the theory of refrigeration.
Air conditioning, like many other things, is fairly simple to service once it is understood. However, there are certain procedures, practices and precautions that should be followed to prevent costly repairs, personal injury or damage to equipment. For this reason it is strongly recommended that this manual be studied thoroughly before attempting to service the Chevrolet system.
The Special Service Tools shown in this manual, or their equivalent, are necessary for the efficient servicing of the Chevrolet Air Conditioning system. All tools listed are available through Kent-Moore Organization, Inc., General Motors Building, Detroit 2, Michigan.
All information, illustrations and specifications contained in this literature are based on the latest product information available at the time of publication approval and the right is reserved to make changes at any time without notice. Changes and supplementary information will be published from time to time in the form of Service News and Service Bulletins. These should be referenced in the blank note pages provided at the back of the manual and in the affected section of the manual to assure that it contains the latest information at all times.
Arrangement of the material is shown by the Table of Contents on the right side of this page. A more detailed index precedes each major subject section.
CHEVROLET MOTOR DIVISION
General Motors Corporation
DETROIT, MICHIGAN
Figure Index
Fig. 1 - Air Outlets and Controls
Fig. 2 - Interior Dash-Mounted Components
Fig. 3 - Air Distributor Schematic
Fig. 4 - Air Flow Schematic
Fig. 5 - Temperature-Pressure Relationship of Freon-12
Fig. 6 - Simplified Refrigeration System
Fig. 7 - Location of Components in Engine Compartment
Fig. 8 - Cycle of Operation Schematic
Fig. 9 - View of Compressor Installed
Fig. 10 - Cutaway View of Compressor
Fig. 11 - Cross-Section of Hand Shutoff Valve
Fig. 12 - Cross-Section of Seal and Clutch Pulley on Compressor Shaft
Fig. 13 - Conditioning Unit
Fig. 14 - Conditioning Unit Removed
Fig. 15 - Adapter with Conditioning Unit Removed
Fig. 16 - View of Expansion Valve, Evaporator and Heater Coils
Fig. 17 - Cross-Section of Expansion Valve
Fig. 18 - Expansion Valve and Evaporator Schematic
Fig. 19 - Condenser and Receiver-Dehydrator
Fig. 20 - Sight Glass
Fig. 21 - Gauge Set
Fig. 22 - Leak Detector
Fig. 23 - Using Leak Detector
Fig. 24 - Freon-12 Disposable Cans and Valves
Fig. 25 - Turning Hand Shutoff Valve
Fig. 26 - Gauge Set Installed
Fig. 27 - Connections for Evacuating
Fig. 28 - Adding Freon
Fig. 29 - Adding Oil (Slight Loss)
Fig. 30 - Checking Expansion Valve Operation
Fig. 31 - Adjusting Expansion Valve
Fig. 32 - Expansion Valve Connections
Fig. 33 - Condenser and Receiver-Dehydrator
Fig. 34 - Conditioning Unit
Fig. 35 - Compressor Installation
Fig. 36 - Exploded View of Compressor and Clutch Pulley
Fig. 37 - Removing Compressor Valve Assembly
Fig. 38 - Seal and Coil Housing "O" Rings
Fig. 39 - Installing Seal
Fig. 40 - Retainer Removed from Seal Seat Groove
Fig. 41 - Installing Oil Slinger
Fig. 42 - View of Clutch Actuating Coil Installed
Fig. 43 - Removing Coil from Housing
Fig. 44 - Locating Coil Retainer Screw Holes
Fig. 45 - Installing Coil Retainer Ring
Fig. 46 - Checking Clearance Between Clutch Armature and Coil Housing
Fig. 47 - Removing Clutch Pulley Assembly
Fig. 48 - Exploded View of Clutch Pulley Assembly
Fig. 49 - Removing Clutch Snap Ring
Fig. 50 - Removing Pulley Bearing Snap Ring
Fig. 51 - Installing Clutch Pulley to Compressor Shaft
Fig. 52 - Tightening Clutch Cover Ring Screws
Fig. 53 - Adjusting Compressor Belt Tension
Fig. 54 - Blower and Thermostatic Switch
Fig. 55 - Fast Idle Linkage
Fig. 56 - Wiring Diagram
Fig. 57 - Air Conditioning Special Tools
Introduction
Since the combinations of temperature and relative humidity which satisfy personal comfort fall within considerably narrower limits than nature usually supplies, a means of controlling these factors is essential if maximum conditions of comfort are to be attained. In addition to the discomfort resulting from too little or too much heat, the atmosphere often seems heavy and unpleasant from the excessive humidity present. Since the moisture content of the air may be close to saturation, body moisture is not absorbed at a satisfactory rate.
The demand for increased body comfort in today's passenger cars has directed attention toward the development of an automotive air conditioning system that will be capable of producing desired comfort for the occupants under all climatic conditions.
Operating on the same basic principles as the modern home air conditioner, the Chevrolet all-weather air conditioning system is designed to provide the controlled temperature and humidity requirements for year around riding comfort. Components of the system are all located compactly under the instrument panel and hood of the car (fig. 1, fig. 2 and fig. 7).
The system operates either on outside air with an automatically varied partial recirculation feature or entirely on recirculated inside air. Outside air is introduced into the system through the cowl intake and immediately passed through the conditioning unit, which contains both a heater core and cooling coils within an insulated housing. A two speed blower directs the air to a distributor mounted on the dash panel inside the vehicle. Conditioned air then enters the passenger compartment through the two instrument panel adjustable outlet nozzles and either the floor distributor or defroster manifold in proportions determined by control settings. Air is recirculated back through the unit from the car interior by means of the return air duct located on the interior of the dash under the distributor.
The desired heating capacity is obtained by metering the flow of engine coolant through the heater core. The de-humidifying feature is achieved by passing incoming air through the cooling coils where excess moisture condenses and is drained from the system. Dirt and dust in the incoming air adheres to the damp surface of the cooling coils and is discharged through the drain along with the condensate. The temperature of incoming air is then raised to the desired level as the air passes through the heater core.
By a simple manipulation of controls, the right combination of
temperature and humidity may be easily obtained regardless of weather
conditions. In addition, inside air may be recirculated through the
system where contaminated air is encountered, such as in concentrations
of slow moving traffic.
Controls
Since the factors which determine the condition of outside air vary independently, they require independent controls. Seven controls (fig. 1) adapt the system to a wide range of such variations.
Five of the controls move through slots in a control panel mounted on the instrument panel to the right of the driver. Two pull-out knobs are mounted on the instrument panel lower flange below the control panel.
The following general description of the system is intended to familiarize the service man with the location and basic function of the . components of the system. The system consists primarily of a conditioning unit and a condensing unit plus other components necessary to obtain proper control and operation of the system. Figure 7 shows the components of the system located in the engine compartment.
The conditioning unit, which is located on the engine side of the dash panel under the hood, consists of all the apparatus necessary to cool and/or heat the air to the quality desired in the passenger compartment. The components of the conditioning unit are the housing, cooling and heating coils, refrigerant control valve, return and fresh air ducts. The refrigerant and hot water connections are piped to connections outside the housing.
The blower and conditioner air duct assembly is mounted on the clash panel inside the passenger compartment and delivers the quantity of conditioned air desired.
Like any refrigeration system, this system, too, must have a condensing unit. A condensing unit may be described as a reclaiming plant since its sole purpose it to reclaim the refrigerant vapor produced in the cooling coil by first compressing and then condensing it into a liquid so that it can be used over and over again. The condensing unit components are located in the engine compartment and consists of the compressor, condenser and receiver dehydrator.
The prime purpose of the compressor is to convert low pressure refrigerant vapor from the cooling coil into a high pressure, high temperature vapor and direct it to the condenser. It utilizes the principle that "when a vapor is compressed, both its pressure and temperature are raised". The compressor is mounted to the right and above the engine block in a special bracket. The compressor is "V" belt driven from the engine through an electromagnetic clutch pulley on the compressor.
The purpose of the condenser, as the name implies, is to condense the high pressure refrigerant vapor that is discharged from the compressor. The high pressure, high temperature vapor produced by the compressor is subjected to the considerably cooler metal surfaces of the condenser mounted in front of the radiator and a change of refrigerant state takes place. This is due to the fundamental laws which state that heat travels from the warmer to the cooler surface and when heat is removed from the vapor, a liquid is produced.
The receiver-dehydrator is used primarily as a liquid storage tank, but functions to trap moisture and foreign matter that may have escaped removal during installation or may have entered the system during service operations.
Other components are necessary to obtain proper control and operation of the system. A cooling thermostat, which is mounted on the air duct, has its thermobulb mounted in the distribution air duct (see Figure 54). When the thermostat contacts are closed, it energizes a coil and closes the contacts in a special relay which is mounted on the right fender skirt. This, in turn, energizes the clutch actuating coil in the compressor assembly, causing the compressor to operate. When the desired temperature in the car has been reached in accordance with the setting of the thermostat, the thermostat contacts open and de-energize the relay coil, which in turn, de-energizes the clutch coil and releases the clutch, causing the compressor to stop operating. Due to the raising and lowering of the temperature in the car, the compressor will cycle "ON" and "OFF" as required.
A heater water control valve is mounted in the inlet hot water line on the engine side of the dash panel. The bulb of the control valve is mounted in the discharge air stream. This valve controls the amount of hot water entering the heating coil.
Connecting hose lines are required to carry the refrigerant liquid and vapor between the cooling coil and the condensing unit. The smaller hose line is called the high pressure liquid fine and the larger hose line connecting the compressor and the cooling coil is the low pressure vapor line. The large hose line between the compressor and the condenser is the high pressure vapor discharge line. A sight glass is located in the high pressure liquid line for quickly determining whether or not the refrigeration charge is sufficient.
To regulate the amount of air conditioning and/or heat desired, certain controls are required. These are located on the instrument panel and are described previously in this manual under "Controls".
Freon-12 refrigerant is used in the Chevrolet system. It is nonpoisonous (except when in contact with an open flame), noncorrosive (except when in contact with water), noninflammable and nonexplosive. However, the fact that Freon-12, which has a boiling point of 21.7°F at sea level pressure is contained under pressure appreciably above atmospheric pressure warrants special handling precautions which are described in this manual "Basic Service Information".
Freon-12 has a definite affinity for oil which greatly assists
in the lubricating of the internal parts of the system. The system is
lubricated by special Frigidaire oil (525 viscosity) available through
parts stock.
Cycle of Operation
Figure 8 presents a schematic arrangement of all the components of the refrigeration system.
Assuming that the control switch is "ON", the thermostat is calling for refrigeration, and the engine and compressor are operating. Low pressure vapor is compressed by the compressor into high pressure vapor and then discharged into the condenser. In the condenser the vapor changes from a high pressure vapor into a high pressure liquid. The liquid then flows into the top of the receiver under pressure.
The high pressure liquid, under pressure, flows from the bottom of the receiver-dehydrator, which acts as a storage tank as well as a moisture remover, through the high pressure line which connects to the sight glass, and on to the high pressure connection of the expansion valve.
At the orifice of the expansion valve, the high pressure liquid changes to a low pressure liquid, due to the operation of the compressor, and enters the cooling coil.
Heat enters the conditioning unit housing from the passenger compartment and through the engine compartment by the action of the blower and some leaks through the insulation of the housing itself. Because the cooling coil is colder than the air surrounding it, some of the heat passes through the refrigerated tubes of the coil into the liquid refrigerant. This absorption of heat causes some of the liquid to vaporize and the vapor is drawn through the low pressure line to the compressor.
The lubrication of the internal parts of the expansion valve is
brought about by the affinity of Freon-12 for oil, causing them to mix
together thoroughly. Even the Freon-12 vapor in a system will carry
globules of oil. As the refrigerant travels through the system in either
a vapor or liquid state, it is carrying through enough oil picked up in
the compressor oil reservoir to keep the moving parts of the valve
lubricated. The compressor is lubricated by the action of the compressor
oil pump and the oil saturated vapor.
Compressor
A five cylinder reciprocating compressor (fig. 9 and fig. 10) is pivot mounted through an adjustable bracket to the water outlet housing and the right exhaust manifold. Intake and exhaust valve reeds at each cylinder effect a definite separation between the discharge (high) side and the intake or suction (low) side of the compressor.
At the rear of the compressor is the compressor head casting which contains the high and low side hand shutoff valve ports and "O" ring gasket seats. In the low side port cavity is a fine mesh intake screen. This screen acts as a filter to prevent the entrance of any undesirable foreign material into the compressor. There is an opening into the high side port cavity for the high pressure relief valve.
The compressor head is mounted to the flange ring on the compressor housing and sealed with a large "O" ring gasket which is partially recessed into the head casting, Provision is made in the bottom of the housing for an oil test elbow with a Schrader type valve.
A high pressure relief valve is provided on the compressor head. Under certain circumstances, the refrigerant pressure on the high side may exceed a safe operating limit. Therefore, to prevent damage to the equipment or the car, the valve is designed to open automatically at approximately 415 pounds per square inch pressure and to close automatically when the pressure is reduced to approximately 300 pounds. Any condition that causes this valve to open should be investigated and steps taken to correct it.
Between the head and the cylinder assembly is the valve plate assembly. On the side of the valve plate facing the compressor head are the five high pressure (discharge) reed valves. On the side of the valve plate assembly facing the cylinder assembly are the five low pressure (suction) reed valves. Under the valve plate and reed assembly is the cylinder assembly which consists of the five cylinders, the needle roller bearing for the main shaft, and the yoke.
A straight mainshaft having different machined diameters for compressor components is supported at one end by the needle roller bearing in the cylinder assembly and by a ball bearing at the front end. The piston and socket plate assembly, which consists of the socket plate assembly, the guide shoe, the piston and rod assembly, the retaining ring and the double row ball bearing, is keyed to the shaft and securely held in place by double set screws. The action of the piston and socket plate assembly can be explained as follows:
As the straight shaft rotates in the needle bearing and in the ball bearing in the bearing holder at the opposite end, the angular bored inner race of the piston and socket plate assembly bearing, which is keyed to the shaft, rotates in the double row bearing which causes the socket plate to move in a circular waving motion. The plate assembly is prevented from rotating by the guide shoe which slides in the yoke of the cylinder assembly. As the pistons are connected to this plate by the piston rods, the pistons will move in and out of the cylinders, resulting in intake to and discharge from the cylinders.
A counter weight is installed on the compressor shaft between the socket plate and the front main ball bearing.
The oil pump is located just forward of the mainshaft ball bearing. The oil is supplied to the oil pump by an oil pick-up tube located along the inside bottom of the compressor shell housing. The oil pump assembly is held in place by a spring wave washer located between the compressor housing and the coil and seal housing.
Another fitting is located on the under side of the compressor
shell and is known as an oil test elbow. It is made of steel and has a
1/4" male flare x 1/4" male pipe thread. A Schrader type core
is fitted in the flare end and a 1/8" I.D. x 3/4" long offset
tube is fitted into the pipe thread end. The 1/4" flare end is
capped with a 1/4" flare nut and deadhead. The Schrader type core
can be opened by depressing the stem.
Hand Shutoff Valves
Mounted on the head of the compressor is the suction (low pressure) and discharge (high pressure) hand shutoff valve assembly. It is fitted to the head with a single screw and the discharge and suction ports are sealed with "O" ring gaskets. Located on the high and low pressure hand shutoff valves (fig. 9 and fig. 10) are fittings for gage connections for determining both high and low side pressures within the system or the compressor.
The bodies of the fittings are steel and are threaded at one end for 1/4" flare connections. The other ends are brazed into the body of the hand shutoff valves at a point just forward of the hand shutoff valve seat to the compressor. A Schrader type core is fitted in the flare end of each fitting. To use the fittings it will be necessary to use a gauge adapter. This adapter is so constructed that when it is installed on the gage fitting, it forces the Schrader core open and permits refrigerant to flow into the gauge fine.
The hand shutoff valves (fig. 11) are back seating valves and should be back seated when the system is m normal operation. With the valves turned completely counterclockwise, the passages to the compressor are connected to the refrigerant lines and open to the gauge fittings. This is normal operating position. When the valve stems are turned completely clockwise, the passages from the compressor to the refrigerant lines are sealed but the passages from the compressor to the gauge fittings remain open. In this position, the evaporator and condenser are shut off from the compressor and the compressor can be removed or serviced.
Both valves should be backed out all the way for normal operation and testing of the system and turned all the way in for servicing or removal of the compressor.
A compressor seal is used to seal the system from the atmosphere when the compressor is operating or is at rest, regardless of the pressures in the compressor. By this it is meant that the system must not leak Freon or oil out of the system or allow air or moisture or dirt to enter the system at any time. The components of the seal are the rotating seat (seal seat), the drive pin, the retaining ring, the small "O" ring, the stationary seat (the compressor shaft seal), and the large "O" ring (fig. 12 and fig. 35).
If it should become necessary to replace a shaft seal due to the seal leaking, all components should be replaced with new parts, except the retaining ring and drive pin. Extreme care should be used when handling the new parts, to prevent marring or even getting the fingers on the highly polished surfaces of the components. The rotating seat is made of alloy cast iron. The polished surface is ground and polished to extreme accuracy. The stationary seat is a graphite compound and is polished to a very flat even surface.
The seal seat is installed on the compressor shaft and the drive pin installed in a drilled hole through the seat into the shaft. This prevents the seat from turning on the shaft. The drive pin is held in place by the retaining ring. An "O" ring is used to seal the seat to the shaft. The compressor shaft seal is installed in the inside cavity in the coil and seal housing and sealed in this housing by an "O" ring. The compressor shaft seal and the coil and seal housing is then installed over the compressor shaft and in the cavity of the compressor housing, and sealed by another "O" ring. The coil and seal housing is mounted to the compressor oil housing by six countersunk screws.
An oil flinger shield is mounted on the compressor shaft. Its
purpose is to prevent oil getting into the clutch pulley in the event of
a shaft seal leak.
Clutch and Pulley Assembly
The clutch pulley, which is mounted to the front of the compressor, is driven by a "V" belt drive from a double pulley on the crankshaft of the engine. The clutch is magnetically operated by a clutch actuating coil and clutch armature and will operate the compressor when refrigeration is required.
The clutch consists of the inner insulating gasket, clutch actuating coil, outer insulating gasket, coil retainer ring, six clutch cover ring bolts and lock washers, clutch cover ring, clutch spring retainer ring, clutch spring, rear clutch plate to which an armature is riveted, three actuating nylon ball bearings, front clutch plate with splined hub, spacer washers or shims (for spacing the air gap between the coil and seal housing containing the clutch actuating coil), and the pulley armature (fig. 12 and fig. 35).
Shims come in three thicknesses-.015", .020", and .025", and by proper selection of shims a .005" variation in clearance can be obtained. When the coil is energized with 12 volts D.C., there should be an air gap of 0.25" to .035" between the coil and seal housing pole pieces and the clutch armature of the clutch pulley.
Completing the clutch and pulley assembly is the retainer ring for the pulley ball bearing, the pulley ball bearing, the grooved pulley, the felt-backed pulley retaining washer and the bolt and lock washer.
When the clutch actuating coil is energized, the seal housing containing the coil becomes magnetized and attracts the armature on the rear clutch plate which, in turn, causes the clutch plate to move back toward the seal housing. The frictional material on the rear clutch plate contacts the inner surface of the clutch cover ring causing the rear clutch plate to rotate with the pulley. Due to the rotating movement of the rear clutch plate, the three nylon balls are caused to roll to the shallow end of the teardrop dimples. This action forces the front clutch plate to move forward and its frictional material contacts the inner surface of the clutch pulley. The movement of the two clutch plates, one to the rear and the other forward, also causes the clutch actuating spring to be compressed. Since the front clutch plate has the splined hub which is fitted to the splined compressor shaft, riveted to it and the pulley is driven by the V-belt drive from the engine pulley, it follows that with the engine running, the complete clutch assembly will be engaged and turning, and will thus cause the compressor to operate.
When the clutch actuating coil is not energized, the seal
housing containing the coil is de-magnetized. The actuating spring then
expands forcing the rear clutch plate in the direction of the front
clutch plate and the front clutch plate in the direction of the rear
clutch plate, thus causing the frictional material of the front and rear
clutch plates to lose contact with the inner surface of the clutch
pulley and the clutch cover ring. Also the three nylon balls are forced
mechanically into the deep depression of the teardrop shaped dimples.
This permits the pulley to rotate or "free wheel" on the
pulley ball bearing without rotating the compressor shaft.
Conditioning Unit
The conditioning unit (fig. 13), which consists basically of the cooling and heating coil assembly and the thermostatic expansion valve contained within a housing, is mounted to the engine side of the dash panel with a yoke or adapter band which clamps around the conditioning unit and an adapter attached to the dash panel. The yoke or adapter band is hinged at the bottom and has two clamping flanges, one on each side. This allows the band to clamp tightly and evenly all the way around. The housing is insulated on the inside with expanded polystyrene. The purpose of the insulation is threefold:
An access cover plate is provided on the housing for adjustment of the expansion valve.
figure 14 and figure 15 illustrate the attachment, design and air flow pattern of the conditioning unit and i. Attaching studs on the back of the unit engage in slots in the adapter. An outside air door, actuated by the "Outside-Inside" air control on the instrument panel opens or closes the unit to outside air through the cowl vent. A flexible valve operates according to the air flow to open or close the passage of return air from the return air duct on the interior of the dash. The blower furnishes the impelling force to pull the air flow through the system to the air distribution duct.
The cooling and heating coil (fig. 16) are in one assembly. The cooling coil may be described as a container for refrigerant liquid and is so designed that it can readily remove heat from the surrounding area after the temperature of the refrigerant liquid is reduced. It is the only place in the system where the refrigerant is changed from a liquid to a vaporous state. This is done by the absorption of heat.
The coils are made of 3/8" copper tubes and 1" button
fins. The cooling coil has a distributor and metering tubes that insure
an even supply of liquid refrigerant to all parts of the coil. It is
known as a multipath coil and is made up of tubes connected in series
and joined together by a distributor at the inlet and by a manifold at
the outlet, thus forming parallel paths of flow. The heating coil has a
manifold at the inlet and outlet and is series-parallel flow. The coils
are mounted to the rear plate in the housing.
Thermostatic Expansion Valve
The purpose of the thermostatic expansion valve (fig. 16) is to regulate the supply of liquid refrigerant according to the requirements of the evaporator (cooling coil). In short, it supplies liquid refrigerant to the cooling coil at the same rate that vaporous refrigerant is removed from the coil.
Figure 17 shows a cross-section of the valve which consists of the power element, body, operating pins (3), stationary seat orifice, needle and needle carriage, adjusting spring and stem. At the high pressure liquid inlet is a fine mesh screen which prevents dirt, filings or other foreign matter from entering the valve orifice. A small fitting called an equalizing line connection is located in the side of the valve.
When the valve is connected in the system, the high pressure liquid enters the valve through the screen from the receiver-dehydrator and passes on to the needle seat orifice. The low pressure liquid leaves the orifice and flows into the coil. The low pressure liquid absorbs heat from the coil and changes to a low pressure vapor, and leaves the coil as such. The power element bulb is clamped to the low pressure vapor line just beyond the outlet of the cooling coil (fig. 16 and fig. 18).
To produce refrigeration a pressure dividing point at the valve is necessary. This is where refrigeration begins. The dividing point between high and low temperature and pressure areas in the thermostatic expansion valve is the needle seat and orifice.
The operation of the valve is quite simple. It is a matter of controlling opposing forces produced by a spring and the refrigerant pressures. For example: The pressure in the power element is trying to push the needle away from the seat, while the adjusting spring is trying to force the needle toward the seat. When the system is not in operation, the refrigerant pressure in the cooling coil is helping the adjusting spring to close the valve. These opposing pressures are established in the design of the valve so that during idle periods the adjusting spring tension and the refrigerant pressure in the cooling coil are always greater than the opposing pressure in the power element. Therefore, the valve remains closed. This means that the only way the valve can be opened, is to turn the switch at the control panel to the "ON" position, so that the compressor can reduce the pressure and temperature of the refrigerant in the cooling coil. When this pressure is reduced to a point where the vapor pressure in the power element becomes the stronger, the needle moves off the seat and liquid starts to flow through the valve orifice into the cooling coil. As long as the switch on the control panel is on, the thermostat calling for refrigeration, and the compressor Operating, the valve will never close and completely shut off the supply of liquid.
The purpose of the power element is to help determine the quantity of liquid that is being metered into the cooling coil. As the temperature of the low pressure line changes at the bulb, the pressure of the vapor in the power element changes, resulting in a change of the position of the valve needle. For example, if the cooling coil gets more liquid than is required, the temperature of the low pressure line is reduced and the resultant lowering of the bulb temperature reduces the pressure of the vapor in the power element allowing the needle to move closer to the seat. This immediately reduces the amount of liquid leaving the valve. Under normal operation, the power element provides accurate control of the quantity of refrigerant to the cooling coil.
The equalizer is required in all high capacity systems. It provides the same pressure in the area opposite the power element as that in the cooling coil. This further helps to keep the cooling unit adequately supplied with liquid refrigerant.
The adjusting stem is provided to increase or decrease the flow
through the valve. Turning the stem counterclockwise increases the flow
while clockwise decreases it (see "Service Operations").
Condenser
The condenser (fig. 19) is of all steel brazed construction. It is of the tube and fin type, having ten tubes connected into inlet and outlet manifolds. Leaving and entering the manifolds in sections of five upper and five lower tubes, the flow is series parallel, with the upper and lower passes of tubes alternating position from inlet to outlet manifolds. The outer surface of the tubes are joined with corrugated metal fins which serve to increase the effective radiation surface. The inlet manifold connection is 5/8" male flare and the outlet manifold connection is 3/8" female flare.
The condenser is mounted in front of the radiator to the radiator support.
The receiver (fig. 19), which serves as a reservoir for storage of high pressure liquid produced in the condenser, is made of heavy gage drawn steel tube. The receiver also incorporates a dehydrating agent which is held in the lower portion of the receiver between two screens.
The most important function of the dehydrator is to accumulate moisture that may have escaped removal during the installation or which may have entered the system during service operations. The importance of keeping the interior of the system free of moisture cannot be overemphasized.
The second duty of the dehydrator is to trap foreign matter, such as particles of dirt, copper filings and bits of solder, which may have accidentally remained in the system, so as to keep them from getting through the expansion valve or coil and into the compressor. No service should be performed on the receiver-dehydrator.
In reality, the sight glass has no function to perform in the system. By this is meant that the system would operate just as well without it. However, it is a valuable addition to the high pressure liquid refrigerant circuit as it will save a lot of time and eliminate some guesswork in diagnosing difficulties. It provides a quick and sure way of determining whether or not the refrigerant charge is sufficient.
The sight glass (fig. 20) has a brass body with the inlet and outlet threaded for 3/8" flare nuts. The refrigerant passes through a small chamber with two small holes which is covered with a sealed glass window. It is so designed that a shortage of refrigerant in the receiver and liquid line will be indicated by the appearance of bubbles or foam beneath the glass. A screw-on metal cap and gasket protects the glass.
The components of the system are connected with flexible hoses and couplings. The flexible hoses are constructed with a synthetic material core, which is then covered with a woven metal mesh. This, in turn, is covered by a woven fabric which is coated to protect it from damage. The connecting couplings are of the ground seat type. Care must be exercised when making connections to use supporting wrenches at all times. This will require the use of three wrenches, namely, one on the ferrule of the hose, one on the fitting, and one on the mating couplings. The ferrule and the fitting should be held stationary while the coupling is being tightened or loosened. The flexible hoses should not be permitted to come in contact with hot manifold of engine nor should they be bent into a radius of less than 10 times their diameter.
The blower assembly (figure 2 and figure 15) is mounted on the inside of the dash panel and consists of a blower wheel and a small motor. The centrifugal or squirrel-cage type blower wheel insures the proper flow of air from the refrigerated area to the ducts leading to the car interior.
The blower wheel is driven by a fractional horsepower, 12 volt,
DC, brush-commutator type motor. It is rated at 1/15 HP, has a speed of
approximately 3200 RPM (counterclockwise rotation) and will operate
within a range of 12 to 14 volts. At full speed the fan has a capacity
for moving 150 cubic feet of air per minute.
Basic Service Information
In any vocation or trade, there are established procedures and practices that have been developed after many years of experience. In addition, occupational hazards may be present that require the observation of certain precautions or use of special tools and equipment. Observing the procedures, practices and precautions of servicing refrigeration equipment will greatly reduce the possibilities of damage to the customers equipment as well as virtually eliminate the element of hazard to the serviceman.
Since the cooling system is exposed to the low temperatures of the refrigeration system at the cooling coils within the conditioning unit, protection must be provided for the cooling system the year around. The cooling system must be protected with anti-freeze to a temperature of +20°F. or below at all times (winter and summer).
The 1955 air conditioning equipment includes a hand throttle to permit increasing engine speeds for improved air conditioning while the car is stopped for short periods. A throttle wire guide stop has been provided to limit engine speed to 900 RPM with transmission in Neutral.
With the fast idle in operation, vehicles equipped with Powerglide transmission should be placed in Neutral when stopped.
It is strongly recommended that the transmission be placed in Neutral with the parking brake "ON" whenever it is necessary to run the engine during servicing of the air-conditioning system.
Extreme care should be observed to avoid accidentally shifting Powerglide equipped vehicles into "D", "L" or "R" positions while fast idle is in operation with vehicle standing still.
Adjustment of the fast idle is described under "Service
Operations".
Precautions in Handling Refrigerant Lines
Freon-12 is a transparent and colorless refrigerant in both the gaseous and liquid state. It has a boiling point of 21.7°F below zero and, therefore, at all normal temperatures and pressures it will be a vapor. The vapor is heavier than air and is noninflammable, nonexplosive, nonpoisonous (except when in contact with an open flame) and noncorrosive (except when in contact with water). The following precautions in handling Freon-12 should be observed at all times.
REMEMBER-"An ounce of prevention is worth a pound of
cure".
Maintaining Chemical Stability in the Refrigeration System
The metal internal parts of the Chevrolet refrigeration system and the refrigerant and oil contained in the system are designed to remain in a state of chemical stability as long as pure Freon-12 plus refrigeration oil is used in the system.
However, when abnormal amounts of foreign materials, such as dirt, air or moisture are allowed to enter the system, the chemical stability may be upset. When accelerated by heat, these contaminates may form acids and sludge and eventually cause the breakdown of components within the system. In addition, contaminates may affect the temperature-pressure relationship of Freon, resulting in improper operating temperature and pressures and decreased efficiency of the system.
The following general practices should be observed to insure chemical stability in the system.
The chart in Figure 5 shows us that every time we raise or lower the temperature of a quantity of Freon-12 liquid, we also raise or lower the pressure on it. Unfortunately this is not done in the same ratio. For example, at 70° the chart shows that the pressure is also 70 pounds. But this is true only at 70°. However, if we know the temperature of the liquid in the cooling coil or the receiver, we can refer to a pressure-temperature table and determine what the pressure should be.
The figures can also be used in a reverse manner. If we know what the pressure is at any point in the system we can refer to the pressure-temperature table and determine what the temperature should be.
The gauge set (fig. 21) is used when purging, evacuating, charging or diagnosing trouble in the system. The gauge at the right is known as the low pressure gage. The face is graduated into pounds of pressure from 0 to 150 and, in the opposite direction, in inches of vacuum from 0 to 30 inches. This is the gauge that should always be used in checking pressures on the low pressure side of the system. When all parts of the system are functioning properly the refrigerant pressure on the low pressure side never falls below 0 pounds pressure. However, several abnormal conditions can occur that will cause the low pressure to fall into a partial vacuum. Therefore, a low pressure gauge is required.
The gauge at the left is graduated from 0 to 300 pounds pressure. This is known as the high pressure gauge and, of course, is used for checking pressures on the high pressure side of the system.
The connection at the right is for attaching the low pressure gauge line and the one at the left the high pressure gauge line. The center connector is common to both and is for the purpose of attaching a line for adding refrigerant, discharging refrigerant, evacuating the system and other uses. When not required, this line or connection should be capped.
The hand shutoff valves on the gauge manifold do not control the opening or closing off of pressure to the gauges. They merely close each opening to the center connector and to each other. During most diagnosing and service operations, the valves must be closed. The only occasion for opening both at the same time would he to bypass refrigerant vapor from the high pressure to the low pressure side of the system, or in evacuating both sides of the system.
A temperature scale for Freon-12 (yellow band) has been provided
on the gauges. The temperatures on this scale are in correct
relationship to the pressures on the outside (white) pressure band,
providing a quick and convenient pressure temperature relationship
reference for Freon-12.
Leak Detector
Leak detector J-6084 (fig. 22) is a propane gas burning torch which is used to locate a leak in any part of the Freon system. Freon gas drawn into the sampling tube attached to the torch will cause the torch flame to change color in proportion to the size of the leak. Propane gas fuel cylinders used with the torch are readily available commercially throughout the country.
CAUTION: Do not use lighted detector in any place where combustible or explosive gases, dusts or vapors may be present.
Insufficient air may be caused by:
Blowing air through the sampling hose and back through the detector will usually clear dirt or foreign matter.
If a continuous yellow flame is caused by a dirty reaction plate, allow the flame to burn for several minutes. This will usually burn the plate clean. If an oxide film appears on the reaction plate from continued use, it will reduce the sensitivity of the detector. This may be remedied by removing the plate, which is attached to the chimney with a single screw, and scraping the surface gently with a knife.
NOTE: Never attempt to clean orifice by passing anything through the hole.
Freon-12 is available through Parts Stock in 25 lb. drums and in 15 oz. disposable cans. Valves are available for the disposable cans, which may be used as individual cans or as a group of three cans connected in series (fig. 24). With three cans connected in series, the total quantity of Freon-12 will be sufficient for a complete charge for the system which requires 2 1/2 pounds of refrigerant. The valves, which are available for either the single can or three can charge through the Kent Moore organization, are installed by piercing the top seal of the cans.
A special refrigeration lubricant, Frigidaire 525 viscosity oil, should be used in the system. It is available in 1 quart graduated bottles through Parts Stock. This oil is as free from moisture and contaminants as it is possible to attain by human processes. This condition should be preserved by immediately capping the bottle when not in use.
The total lubricant capacity of the compressor is 9 ounces (avoirdupois).
The compressor serial number is located on the serial number plate
on top of the compressor. The serial number consists of a series of
numbers containing the letters XB (Example: 48XB959). This serial number
should be referenced on all forms and correspondence related to the
servicing of this part.
Inspection and Periodic Service
This test may be conducted to determine if the system is performing in a satisfactory manner and should be used as a guide by the serviceman in diagnosing trouble within the system.
The following fixed conditions must be adhered to in order to make it possible to compare the performance of the system being tested with the standards below.
The following performance data define normal operation of the system under above conditions.
Ambient Discharge Suction Right Hand
Temperature Pressure Pressure Discharge
(at Radiator (High Side (Low Pressure Nozzle
Grille) Pressure) Gauge) Temperature
70°F 155±10# 14±2# 44°F
80°F 190±10# 17±2# 44°F
90°F 225±10# 20±2# 44°F
100°F 255±10# 23±2# 48°F
Whenever trouble develops in the refrigeration system, the diagnosis procedure listed below for the particular condition encountered, will assist in locating the source of trouble.
Symptoms and Probable Cause
Diagnosis Procedures
Drafts
a. Poor air distribution.
a. Readjust air outlets.
b. Car temperature too low.
b. Check thermostatic switch for stuck closed points and improper
thermobulb location. Check relay for stuck points. Check control panel
linkage. Check clutch pulley for constant engagement.
Shortage of Air Supply at Outlets
a. Car temperature up.
a. Check fan speeds. Check cooling coil for air passage. Check
position of air dampers.
b. Low fan speed.
b. Check voltage at fan motor. Check motor bearings. Check
direction of motor rotation
Air Noise
a. Sharp obstruction in air stream.
a. Check internal surfaces of ducts and smooth out kinks or rough
edges.
b. Small slits in ducts.
b. Check ducts and close all holes or openings.
c. Obstruction in outlets or ducts.
c. Check for partly covered outlets, loose materials in ducts or fan
housing and loose dampers in ducts.
Scraping Noise
a. Fan hitting fan housing.
a. Adjust fan to turn free on all sides. Check motor bearings.
Tighten motor mountings.
Rattle and Vibration Noises
a. Loose ducts, tubing or compressor mounting.
a. Check duct, tubing, tubing clamps, compressor and compressor
mounting for looseness and tighten where required.
b. Cooling coil mounting bolts loose.
b. Tighten or install new bolts.
Water Leaking or Dripping Into Passenger Compartment
a. Drip pan or drain opening stopped up.
a. Clean drip pan and drain openings.
b. Housing sweating.
b. Check insulation in housing.
Hissing Noise at Expansion Valve
a. Shortage of refrigerant (indicated at sight glass).
a. Locate and repair leak and add refrigerant.
b. Restriction in liquid line.
b. Check receiver-dehydrator for partial stoppage. Check filter
screen at expansion valve. Check line for kinks.
Diagnosis Continued
Partial Frosting and Sweating of Cooling Unit or Poor
Cooling
a. Shortage of refrigerant (indicated at sight glass).
a. Locate and repair leak and add refrigerant.
b. Expansion valve improperly adjusted.
b. Check valve operation and adjust if necessary.
c. Restricted or clogged liquid line.
c. Check receiver-dehydrator for partial stoppage.
d. Improperly installed or adjusted control panel linkage
d. Check control linkage to thermostatic switch and water control
valve.
Failure to Cool
a. Faulty expansion valve.
a. Expansion valve out of adjustment. Adjust valve as required.
Discharged power element. Replace valve. Stopped up expansion valve
filter screen. Replace screen.
b. Stopped up liquid line or receiver dehydrator.
b. Check for stoppage and replace if necessary.
c. Faulty thermostatic switch operation.
c. Check fuse. Check linkage from control panel to both
thermostatic switch and hot water control valve. Check thermostatic
switch bulb location. Check thermostatic switch contacts and terminal
connections. Check relay contacts and terminal connections. Check
clutch actuating coil connections and coil.
d. Faulty clutch operation.
d. Check clutch for slippage by watching bolt in center of
compressor shaft. Bolt should be turning at same speed as pulley.
Check for belt slippage. Check air gap which should be .025" to
.035". Remove and check internal parts of clutch and replace where
necessary.
e. Lost refrigerant charge (complete charge).
e. Locate and repair leak, process and charge system and check for
proper oil level.
f. Blower not operating properly.
f. Check electrical circuit. Check motor and fan.
g. Insufficient air.
g. Check motor speed. Check for restrictions in ducts. Check for
dirty coils (refrigeration and heating). Remove coils to clean as
necessary.
h. Heater thermostat does not cut off circulation of the engine
coolant through the heater core with HEAT control in "off"position.
h. Check temperature of copper tube entering conditioning unit
below upper heater hose. Coolant from heater control thermostat flows
through this tube and if hot coolant flow is indicated, adjust controls
or replace thermostat.
Too Cool
a. Faulty thermostatic switch.
a. Check switch setting and control panel linkage to switch. Check
location of switch thermobulb. Check contacts in switch and clutch coil
relay.
b. Faulty clutch.
b. Check for stuck clutch. Remove and disassemble pulley, check
parts and replace where necessary.
High Gauge Reading on High Side of System
a. Air or excessive refrigerant in system.
a. Check complete system for leaks. Where detected, repair leaks,
discharge system, then process system and recharge system with a
complete charge.
b. Blocked air circulation through condenser.
b. Clean condenser with stiff brush, compressed air or cool water.
Never use steam!
c. High engine temperature.
c. Perform required engine maintenance.
Low Gauge Reading on High Side of System
a. Shortage of refrigerant.
a. Check for shortage, locate leak and repair. Add refrigerant as
required.
b. Faulty compressor.
b. Replace serviceable parts or compressor.
High Gauge Reading on Low Side of System
a. Over-feeding of expansion valve.
a. Check expansion valve for poor bulb contact to suction line.
Check valve adjustment.
b. Faulty compressor.
b. Replace compressor if found to be faulty.
c. Excessively high head or high side pressure
c. Check system for leaks. Repair any leaks found, discharge and
process system, then recharge.
d. Clutch slipping.
d. Check clutch and make necessary repairs.
Low Gauge Reading on Low Side of System
a. Restriction in liquid line, suction line receiver-dehydrator or
screen at expansion valve.
a. Check lines for kinks and replace lines if kinks are found.
Check receiver-dehydrator. If partly stopped up, it will be cold or
frosted. Check expansion valve. If partly stopped up, it will be cold or
frosted at that point. Valve may also be adjusted incorrectly by being
closed off too much.
b. Cooling coil dirty or iced up.
b. Check cooling coil. If dirty, clean coil with cold water. If
iced up defrost coil and check expansion valve operation.
c. Clutch will not engage.
c. Check thermostat switch contacts and bulb location. Check relay
contacts. Remove clutch pulley and replace internal parts of clutch if
necessary.
d. Shortage of refrigerant.
d. Check for leak, repair leak
and recharge system.
Diagnosis Summary
High Head Pressure Indications
Low Head Pressure Indications
Shortage of Refrigerant Indications
Continuous Operation of Compressor Indications
Poor or No Refrigeration Indications.
Inability to Obtain Proper Expansion Valve Adjustment
Stuck Open Needle in Expansion Valve Indications
Stuck Shut Needle in Expansion Valve Indications
In removing and replacing any part in the refrigeration system except the compressor, the following operations, which are described in this section, must be performed in the sequence shown.
CAUTION: Always wear protective goggles when working on refrigeration systems. Goggles J-5453 are included in the set of air conditioning special tools. Also, beware of the danger of carbon monoxide fumes by avoiding running the engine in closed or improperly ventilated garages.
Testing the system for refrigerant leaks is accomplished with Leak Detector J-6084, a propane gas-burning torch which is described under "Basic Service Information."
Whenever a leak is suspected in the system or a service operation performed which results in disturbing lines or connections, it is advisable to test for leaks. Common sense should be the governing factor in performing any leak test, since the necessity and extent of any such test will, in general, depend upon the nature of the complaint and the type of service performed on the system. It is better to test and be sure, if in doubt, than to risk the possibility of having to do the job over again.
In replacing any of the air conditioning components except the compressor the system must be completely purged or drained of refrigerant. The purpose is to lower the pressure inside the system so that a component part can be safely removed.
The complete system has now been purged of Freon and any part in the system can be replaced.
The system is now ready for complete charge (2 1/2 lbs.
Freon-12). Do not remove gauge set or jumper wire after evacuation, but
proceed with charging operation as described below.
Adding Refrigerant
An important rule to follow in charging is that refrigerant should always be added to the compressor in a vaporous state. Another important rule is never to add refrigerant until the system has been leak tested and properly processed.
In order to charge refrigerant in the vapor state, the Freon-12 drum will require the use of some heat. This can best be accomplished by placing the drum or cans in an upright position in a bucket or container of warm water. The temperature of the water should not exceed 125°F. Since the temperature of the water and drum will decrease, as the vapor leaves the drum, the water and drum will be cooled. This may result in a lowering of the drum pressure to the extent where it will be necessary to replenish or re-heat the water.
With the compressor in operation, the high pressure should not exceed 275 lbs. and the drum pressure should always be maintained at a minimum of 12 pounds and should not exceed a maximum of 90-100 pounds. Refer to "Basic Service Information" for a description of gauge set valve operation.
In some instances it may be more advantageous to purge all refrigerant from the system and add a complete charge than to replenish smaller losses in the system. This may be particularly true in cases where Freon-12 is stocked in disposable cans or scales are not available. Where it is desired to purge the system and add a complete charge, perform the operations as described under "Air or Excessive Refrigerant in the System" in this section. The following procedure for adding a partial charge may be used where suitable scales are available.
If a refrigerant leak is found which indicates some loss of oil by the presence of oil around the leak, or if it is necessary to determine whether or not the compressor has a sufficient amount of oil, the following procedure should be used after making necessary repairs.
NOTE. Refer to Figure 29.
The compressor was originally charged with 9 ounces (avoirdupois) of Frigidaire 525 viscosity oil. If any major loss of oil has occurred, such as a seal leak, line breakage, etc., the procedure described below should be followed. Any leak should be located and repaired before proceeding with this operation prior to evacuating and recharging the system.
The procedure outlined below is to be used when a diagnosis indicates either air or excessive refrigerant in the system. When a higher than normal high side operating pressure is encountered (see "Service Diagnosis"), then proceed as follows to purge and recharge the system.
To determine if the expansion valve is operating properly, proceed as follows:
If these adjustments do not produce satisfactory results, then the liquid inlet screen may be clogged, the valve thermobulb unit may not be properly positioned or clamped to the low pressure Freon line leading from the evaporator, or the valve assembly may require replacement (see "Replacement of Valve Assembly" described below).
After attempting adjustment of the expansion valve, but before replacing the valve, make certain the liquid inlet screen is not clogged (see Figure 17). This operation may be performed after the conditioning unit has been removed and the expansion valve side of the unit housing disassembled (fig. 32) as described below. After checking the screen and the location and mounting of the thermobulb, proceed with replacement of the valve assembly. A malfunctioning valve may result from a stuck open or shut needle caused by corrosion or a discharged power element caused by a broken capillary line or tip.
Since the receiver-dehydrator and the sight glass are both in the high pressure liquid line, the procedure for replacing the sight glass will be the same as for replacing the receiver-dehydrator. Refer to "Receiver-Dehydrator Replacement" described below for processing the system before and after removal of the sight glass.
The receiver-dehydrator should be replaced if it has been damaged through an accident or if it leaks or becomes restricted or clogged.
If at any time when examining the compressor oil, moisture is found or there is an indication of moisture at the expansion valve needle, the receiver dehydrator should be replaced as follows:
If the condenser becomes damaged through accident or collision, or develops a leak, it should be replaced as follows:
If the flexible lines become damaged through accident or collision, or develop leaks, they should be replaced. Use only sealed lines from parts stock as replacement lines.
The coil assembly, which consists of the evaporator or cooling coils and the heater coils, is located in the conditioning unit. If a leak develops in any of the tubes or soldered joints or if one becomes damaged, the assembly should be replaced.
If the assembly is being replaced due to a refrigerant leak, first check to make sure the leak is not coming from one of the flares or threaded fittings at the expansion valve, then proceed with the replacement operation as follows:
NOTE: Refer to figure 14, figure 32 and figure 34.
A malfunctioning compressor is one that will not turn over, has stuck crankshaft or pistons, burnt bearings, broken discharge or suction reeds or some internal difficulty which prevents the compressor from operating properly.
When such a difficulty is encountered, the compressor should be removed and a new compressor installed.
A new service compressor does not include clutch actuating coil parts, clutch pulley parts, or the hand shutoff valve assembly. A service shipping plate is bolted over two "O" rings to seal the valve port openings. The two "O" rings under the shipping plate should be transferred to the old assembly and two new "O" rings used when installing the compressor on the car. A new compressor is charged with nine ounces of Frigidaire 525 Viscosity Oil, and a mixture of Freon-12 and nitrogen under approximately 5 psi pressure. An envelope attached to the compressor contains two .015" shims, two .020" shims, and one .023" shim to insure a sufficient number of shims for the compressor clutch adjustment.
Since the service compressor will be received less clutch actuating coil, clutch pulley and hand shutoff valve assembly, these components will normally be removed from the malfunctioning compressor and reinstalled on