The compressor is located at the lower front right side of the engine. The compressor's function is to compress low pressure refrigerant vapor into high pressure, high temperature vapor.

The compressor is a variable displacement rotary vane type pump. The compressor uses a control valve to automatically vary its displacement as system heat loads change. The displacement can vary from 6.5 percent (9 cc) to 100 percent (140 cc).

The electromagnetic clutch engages the compressor when the A/C button in depressed. The clutch consists of a drive plate, pulley, and a coil assembly. The drive plate is bolted to the compressor shaft. The pulley and bearing assembly is press fit onto the compressor hub, and the coil assembly is screwed to the compressor body. A thermal link fuse is incorporated into the coil. If the temperature of the coil exceeds 214°C +/- 3°C (417°F +/- 37°F), the link will melt creating an open coil circuit. When the coil is de-energized the drive plate releases the pulley and the compressor stops pumping. A typical coil resistance will measure 3.22 +/- 0.08 ohms at 22°C (72°F).

A diode is used to protect the vehicles electrical circuits from the collapsing electrical field of the coil. This diode is located in the UHFB.

To protect the A/C system from high pressure, a pressure relief valve is located in the front head of the compressor. This valve will open at 3620 kPa +345/-245 kPa (525 psi) +50 psi -35 psi and reseat at 2930 kPa (425 psi). If this valve ever opens the A/C system must be serviced and the valve must be replaced.

The A/C compressor will be controlled by PCM/ECM/BCM control logic under the following conditions:

Coolant Temperature

A/C System Pressure

Evaporator Low Ambient Protection (ELAP)

ELAP is a BCM controlled cycling of the compressor clutch to prevent freezing of the evaporator core. ELAP is only enabled at ambient temperatures between 0-20°C (32-68°F).

Cooling Fan Logic

There are two cooling fans -- a pusher and a puller. The fans run together at 3 different voltage levels to create 3 speeds or stages.

The fan speed selected is based on coolant temperature or A/C system high side pressure.

L61

L81

The condenser is located forward of and is mounted to the radiator. The condenser design is similar to that of a radiator with a multiple tube cross flow pattern. The condenser transfers heat from the high temperature refrigerant gas to the air, causing the refrigerant to condense into a liquid. This condensed refrigerant then flows out to the receiver/dehydrator assembly. The cooling capacity of the condenser will be diminished if the condenser fins are not kept clean and straight.

The receiver/dehydrator (R/D) is located to the left of the condenser and is mounted in a bracket which is welded to the condenser. Its purpose is to act as a reservoir for liquid R134a refrigerant received from the condenser. A constant flow of liquid refrigerant must be supplied to the TXV to allow it to regulate properly. The R/D assembly also contains a desiccant bag which absorbs any moisture that may have entered the system. The R/D assembly should be replaced any time it has been open to the atmosphere for an extended period of time as the desiccant will become saturated.

The thermal expansion valve (TXV) is installed on the evaporator inlet and outlet pipes. The thermal expansion valve converts the high-pressure liquid refrigerant from the receiver/dehydrator to a low-pressure liquid refrigerant by forcing it through a small port before entering the evaporator.

When the heat load increases or decreases, the expansion valve will supply the correct quantity of refrigerant to the evaporator for maximum heat transfer.

The expansion valve consists of the block and body.

The body includes a temperature sensor for sensing the temperature of vapor. A diaphragm transmits changes in pressure inside the temperature sensor bulb stem which is connected to the diaphragm.

The stem is tapered and moves in response to changes in the pressure inside the temperature sensor bulb. This controls the flow of refrigerant by changing the size of the valve opening.

The body has an equalizing pressure port through which the vapor pressure of the evaporator acts on the bottom of the diaphragm.

When the evaporator heat load increases, the stem is pushed down and the flow of refrigerant to the evaporator increases. As a result, the vapor pressure and temperature of the refrigerant on the evaporator outlet side changes. When the evaporator heat load decreases, the situation is reversed.

The heater core heats the air before it enters the passenger compartment. Engine coolant is circulated through the core to heat the air passing over the fins of the heater core.

The heater core is functional at all times, no water valve and may be used to temper air in A/C mode as well as heat, vent, bi-level, and defrost modes.

The evaporator core cools and dries the air before it enters the passenger compartment. When the A/C is ON, the evaporator is cooled by refrigerant. As warm moist air passes through the core, the air is cooled causing the moisture to condense on the fins of the core.

This dry cool air can then be blown into the passenger compartment for cooling or directed through the heater core to be warmed. The evaporator core can be serviced through a service door on the right side of the module.

The recirculation actuator allows the operator to select between fresh air from outside the vehicle or recirculation of air in the passenger compartment. When the recirculation button is depressed, the actuator rotates 2 doors simultaneously to change the air source. The right side door is driven directly from the actuator. The left side door is linked to the right side door by an adjustable rod. This module does not have any outside air bleed when recirculation is selected.

The blower motor is a permanent magnet motor with a split squirrel cage fan. Its purpose is to provide air flow to the passenger compartment on standard HVAC vehicles. The blower speeds are controlled in all modes by a 5 position rotary switch. On automatic climate control vehicle the blower speeds are variable dependent on the rotary knob position.

The blower motor and fan is located below the passenger compartment air filter.

The air distribution system allows airflow to be directed to the windshield, I/P outlets, side windows, and front and rear foot areas. The defroster, side window defoggers, and I/P outlet ducts are built into the I/P assembly and are not serviceable. The side window defog outlets are connected to the defroster duct and therefore function when defrost is selected. Heater ducts are connected to the left and right side of the HVAC module and direct heat to each front foot well area. Rear seat heat is provided through a connector duct at the bottom of the module which then feeds left and right rear seat heater ducts.