Operation CHARM: Car repair manuals for everyone.

Component and System Operation

COMPRESSOR
R-4 compressors are driven by a belt from the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates freely without turning the compressor shaft, until an electro- magnetic clutch coil is energized. When voltage is applied to energize the clutch coil, a clutch plate and hub assembly is drawn rearward toward the pulley. The magnetic force locks the clutch plate and pulley together as one unit to drive the compressor shaft.

All replacement compressors from service parts will have 240 ml (8 fl. oz.) of oil in the crankcase, the oil must be drained and retained. Then replace the oil in the same amount as previously recorded from the old compressor.

PRESSURE RELIEF VALVE
The compressor is equipped with a pressure relief valve which is placed in the system as a safety factor. Under certain conditions the refrigerant on the discharge side may exceed the designed operating pressure. To prevent system damage, the valve is designed to open automatically at approximately 3036 kPa (440 psi). Any condition that causes this valve to open should be corrected, and the refrigerant oil should be replaced as necessary.

Accumulator:






ACCUMULATOR
The sealed accumulator assembly is connected to the evaporator outlet pipe. It functions as a liquid-vapor separator that receives refrigerant vapor, some liquid refrigerant and refrigerant oil from the evaporator. It only allows refrigerant vapor and oil to continue on to the compressor.

At the bottom of the accumulator is the desiccant which acts as a drying agent for moisture that may have entered the system. An oil bleed hole is also located near the bottom of the accumulator outlet pipe. to provide an oil return path to the compressor.

A low-side pressure schrader-type valve service fitting is located near the top of the accumulator. A similar schrader-type fitting is provided for mounting the pressure cycling switch. It is not necessary to discharge the system to replace the switch. The accumulator is serviced only as a replacement assembly.

Expansion (Orifice) Tube:






EXPANSION (ORIFICE) TUBE
The plastic expansion tube, with its mesh screen and orifice, is located in the liquid line between the condenser and the evaporator. It provides a restriction to the high-pressure liquid refrigerant in the liquid line, metering the flow of refrigerant in the liquid line, metering the flow of refrigerant to the evaporator as a low-pressure liquid. The expansion tube and orifice are protected from contamination by filter screens on both inlet and outlet sides. The tube is serviced only as a replacement assembly.

When the engine is turned "OFF" with the air conditioning operating, the refrigerant in the system will flow from the high-pressure side of the expansion tube (orifice) to the low-pressure side until the pressure is equalized. This may be detected as a faint sound of liquid flowing (hissing) for 30 to 60 seconds and is a normal condition.


CONDENSER
The condenser assembly in front of the radiator is made up of coils, which carry the refrigerant and cooling fins to provide rapid transfer of heat. The air passing through the condenser cools the high-pressure refrigerant vapor, causing it to condense into a liquid.


COOLANT FAN
The coolant fan operation is crucial to the proper operation of the A/C system. The coolant fan ensures the proper amount of air flow across the condenser throughout the vehicles operating range.

The fan operation should be checked during any A/C diagnosis procedure. Special attention should be given to the fan whenever excessive high-side pressures are encountered, the high-pressure relief valve discharges, or if the high-side high-pressure cut-off switch opens.

EVAPORATOR
The evaporator is a device which cools and dehumidifies the air before it enters the vehicle. High pressure liquid refrigerant flows through the orifice tube into the low-pressure area of the evaporator. The heat in the air passing through the evaporator core is lost to the cooler surface of the core, thereby cooling the air. As the process of heat loss from the air to the evaporator core surface is taking place, any moisture (humidity) in the air condenses on the outside surface of the evaporator core and is drained off as water:

HEATER CORE
In any air conditioning mode, the heater core can be used to heat the cool dehumidified air to achieve the desired temperature. The position of the control assembly temperature lever will determine how much heat will be added to the incoming air.