System Components Description

System Components Description

Functional

Compressor
All compressors are belt-driven from the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates without driving the compressor shaft until an electromagnetic clutch coil is energized. When voltage is applied to energize the clutch coil, the 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.

As the compressor shaft is driven, it compresses the low-pressure refrigerant vapor from the evaporator into a high-pressure, high-temperature vapor. The refrigerant oil which is used to lubricate the compressor is carried with the refrigerant. Refer to V5 A/C System Description.

Condenser Core
The condenser assembly in front of the radiator consists of coils which carry the refrigerant, and cooling fins that provide the rapid transfer of heat. The air passing through the condenser cools the high-pressure refrigerant vapor and causes it to condense into a liquid.

Expansion Valve
The expansion valve is located with the evaporator core, on the front passenger side fire wall. The expansion valve can fail in three different positions: open, closed, or restricted. An expansion valve that fails in the open position will result in a noisy A/C compressor or no cooling. The cause can be a broken spring, a broken ball, or excessive moisture in the A/C system. If the spring or the ball are found to be defective, replace the expansion valve. If excessive moisture is found in the A/C system, recycle the refrigerant.

An expansion valve that fails in the closed position will result in low suction pressure and no cooling. This may be caused by a failed power dome or excessive moisture in the A/C system. If the power dome on the expansion valve is found to be defective, replace the expansion valve. If excessive moisture is found in the A/C system, recycle the refrigerant.

A restricted expansion valve will result in low suction pressure and no cooling. This may be caused by debris in the refrigerant system. If debris is believed to be the cause, recycle the refrigerant, replace the expansion valve, and replace the receiver-dryer.

Evaporator Core
The evaporator is a device which cools and dehumidifies the air before it enters the vehicle. High-pressure liquid refrigerant flows through the expansion tube orifice and becomes a low-pressure gas in the evaporator. The heat in the air passing through the evaporator core is transferred to the cooler surface of the core, which cools the air. As the process of heat transfer from the air to the evaporator core surface is taking place, any moisture or humidity in the air condenses on the outside surface of the evaporator core and is drained off as water.

Receiver-Dryer
The sealed receiver-dryer assembly is connected to the condenser outlet pipe. It acts as a refrigerant storing container, receiving liquid, vapor, and refrigerant oil from the evaporator. At the bottom of the receiver-dryer is the desiccant, which acts as a drying agent for the moisture that may have entered the system. An oil bleed hole is located near the bottom of the receiver-dryer outlet pipe to provide an oil return path to the compressor. The receiver-dryer is serviceable only as an assembly.

Heater Core
The heater core heats the air before it enters the vehicle. Engine coolant is circulated through the core to heat the outside air passing over the fins of the core. The core is functional at all times and may be used to temper conditioned air in the A/C mode as well as in the heat or the vent
modes.

Control

Controller
The operation of the A/C system is controlled by the switches and the lever on the control head. The compressor clutch and the blower are connected electrically to the control head by a wiring harness. The blower circuit is open in the OFF mode. Airflow is provided by the four blower speeds available in the remaining modes. Cooled and dehumidified air is available in the MAX, NORMAL, BI-LEVEL, and DEFROST modes.

The temperature is controlled by the position of the temperature knob on the control head. A cable connects this knob to the temperature door, which controls the airflow through the heater core. As the temperature knob is moved through its range of travel, a sliding clip on the cable at the temperature valve connection should assume a position ensuring that the temperature door will seat in both extreme positions. The temperature door position is independent of the mode control switch. The temperature door on some models is controlled electrically, eliminating the need for the temperature cable.

The electric engine cooling fan on some vehicles is not part of the A/C control system; however, the fan is operational any time the A/C control is in the MAX, NORMAL, or BI-LEVEL modes. Some models provide for engine cooling fan operation when the controller is in the DEFROST mode. This added feature is part of the A/C controller function and is aimed at preventing excessive compressor head temperatures. It also allows the A/C system to function more efficiently. On some models, the engine cooling fan will be turned off during road speed conditions above 56 km/h (35 mph), when the airflow though the condenser coil is adequate for efficient cooling. The operation of the cooling fan is controlled by the powertrain control module (PCM), or the engine control module (ECM), through the cooling fan relay.

Pressure Transducer
The pressure transducer incorporates the functions of the high-pressure and the low-pressure cutout switches along with the fan cycling switch. The pressure transducer is located in the high-side liquid refrigerant line near the right front strut tower and the air filter assembly.

Wide-Open Throttle (WOT) Compressor Cutoff
During full throttle acceleration on vehicles equipped with multi-port injection (MPI), the throttle position sensor (TPS) sends a signal to the PCM or the ECM, which then controls the compressor clutch.

A/C Time Delay Relay
This relay on some vehicles controls the current to the entire A/C system and provides a short delay of A/C operation upon start-up.