System Components

System Components:

COMPRESSOR

The compressor performs two major functions. It compresses the low-pressure refrigerant vapor from the evaporator into a high-pressure, high temperature vapor. The compressor also pumps refrigerant (and refrigerant oil) through the A/C system.

MAGNETIC CLUTCH

The compressor is belt-driven from the engine crankshaft through the compressor pulley. When the air conditioner is not operating the pulley turns freely. When the A/C is turned "ON" the magnetic clutch engages the pulley and the compressor begins pumping.

CONDENSER

The condenser is mounted in front of the radiator and for the most part, looks like a small radiator. It is made up of coils which carry refrigerant and heat fins which provide rapid heat transfer. Air passing through the condenser cools the high-pressure, high-temperature refrigerant vapor, "condensing" it to liquid.

COOLANT FAN

The coolant fan is crucial to the proper operation of the A/C system. The fan ensures a sufficient amount of airflow across the condenser throughout the vehicle's operating range. The fan should be checked during A/C diagnosis procedures. Special attention should be given to the fan whenever excessive high-side pressure is encountered.

EXPANSION VALVE

The expansion valve regulates flow of the liquid refrigerant into the evaporator, resulting in a drop in temperature and pressure.

EVAPORATOR

The evaporator is housed in the Evaporator Case, located behind the right side of the instrument panel. It cools and dehumidifies the air before it reaches the passenger compartment. High-pressure liquid refrigerant flows through the expansion tube and valve, becoming a low-temperature, low-pressure liquid and enters the evaporator. The cold liquid cools the coils and fins of the core, and heat in the air is drawn to the cooler surface of the evaporator core, cooling the air. This heat transference changes the refrigerant from a low-pressure liquid to a low-pressure vapor.

RECEIVER/DRYER

The receiver/dryer performs three functions:

A. It serves as a temporary storage container for condensed liquid refrigerant.
B. The dryer removes dirt and moisture from the refrigerant by means of a filter and desiccant bag.
C. The sight glass, installed atop the receiver serves to show the state of the refrigerant flow.

VACUUM SWITCHING VALVE

At low idling speeds the compressor exerts an excessive load on the engine. To prevent stalling, the vacuum switching valve utilizes inlet manifold vacuum to increase engine idle speed. The vacuum switching valve sends signals to the engine control module (ECM) and to the A/C amplifier.

PRESSURE SWITCH

A pressure switch is used to stop compressor operation when the refrigerant pressure is abnormally high or low due to leakage or insufficient refrigerant. The switch is located in the high-pressure line behind the receiver/dryer.

COOLANT TEMPERATURE SWITCH

An engine coolant temperature switch is used to stop A/C operation if the engine begins to overheat. The switch will cut off A/C operation at 103°C (217°F).

THERMISTOR

When the evaporative temperature of the refrigerant drops to 1°C (34°F) or below, the evaporator fins will develop frost or ice, reducing the airflow and lowering the unit's cooling capacity. The thermistor is a sensor which is used to prevent this icing in the evaporator. Located on the evaporator, the thermistor converts core temperature into a resistance value, which is sent to the A/C amplifier.

AIR CONDITIONER AMPLIFIER

The A/C amplifier monitors the operations of the vacuum switching valve, magnetic clutch, thermistor and condenser cooling fan based on signals received from various engine sensors. It coordinates all the information received from the sensors and, in conjunction with the ECM, physically controls the A/C system. It is installed in the evaporator case.

With the A/C system operating, the amplifier control functions are as follows:

^ Idle speed control (in conjunction with the vacuum switching valve).
^ Magnetic clutch delay-0.8 seconds after the vacuum switching valve is engaged.
^ A/C cutoff control-high refrigerant pressure, low refrigerant pressure, engine coolant overheating, engine cranking, low evaporator temperature, during rapid vehicle acceleration.

CONDENSER FAN AND MAGNETIC CLUTCH RELAYS

These relays control the flow of electric current to the condenser fan motor and the magnetic clutch relay.