A/C Controls

CONTROLS

Fig.1 Compressor Clutch - Typical:

COMPRESSOR CLUTCH
The compressor clutch assembly consists of a stationary electromagnetic coil, a hub bearing and pulley assembly, and a clutch plate. The electromagnetic coil unit and the hub bearing and pulley assembly are each retained on the nose of the compressor front housing with snap rings. The clutch plate is mounted to the compressor shaft and secured with a nut.

The compressor clutch assembly provides the means to engage and disengage the compressor from the engine serpentine accessory drive belt. When the clutch coil is energized, it magnetically draws the clutch into contact with the pulley and drives the compressor shaft. When the coil is not energized, the pulley freewheels on the clutch hub bearing, which is part of the pulley. The compressor clutch and coil are the only serviced parts on the compressor.

The compressor clutch engagement is controlled by several components: the heater-A/C mode control switch, the low pressure cycling clutch switch, the high pressure cut-off switch, the compressor clutch relay, and the Powertrain Control Module (PCM). The PCM may delay compressor clutch engagement for up to 30 seconds.

A/C PRESSURE TRANSDUCER
The A/C pressure transducer is an electromechanical device that functions as the refrigerant system pressure sensor. The PCM uses information from the transducer to control the radiator fans and compressor functions. The sensor is attached to a threaded valve on the liquid line.

The pressure transducer turns OFF the voltage to the compressor clutch coil when refrigerant gas pressure drops to levels that could damage the compressor. The transducer also is used to adjust condenser fan speeds and will turn OFF compressor at high refrigerant pressures. The pressure transducer is a sealed factory calibrated unit. It must be replaced if defective. O-ring replacement is required whenever the pressure transducer is serviced. Be sure to use the O-ring specified for the transducer.

BLOWER MOTOR AND WHEEL ASSEMBLY
The blower motor wheel is only serviced with the blower motor. The wheel and the motor are balanced as an assembly. If the blower motor wheel requires replacement, the blower motor must also be replaced.

BLOWER MOTOR RESISTOR
The blower motor resistor is mounted in the bulkhead on the passenger side of the vehicle under the cowl trim cover. It can be accessed for service by removing the cowl trim cover.

The resistor has multiple resistor wires, each of which will change the resistance in the blower motor ground path to change the blower motor speed. The blower motor switch directs the ground path through the correct resistor wire to obtain the selected blower motor speed.

With the blower motor switch in the lowest speed position, the ground path for the motor is applied through all of the resistor wires. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed. When the blower motor switch is in the highest speed position, the blower motor resistor is bypassed and the blower motor receives a direct path to ground.

The blower motor resistor cannot be repaired and, if faulty or damaged, it must be replaced.

EVAPORATOR FIN SENSOR
The evaporator fin sensor is located in the heater A/C housing and placed in the evaporator fins. The evaporator fin sensor can be replaced without having to remove the heater-A/C housing from the vehicle.

The sensor prevents evaporator freeze-up. This is done by cycling the compressor clutch OFF when evaporator temperature drops below freezing point. It cycles ON when the evaporator temperature rises above freezing point. The evaporator fin sensor uses a thermistor probe in a capillary tube. The tube is inserted between the evaporator fins in the heater- A/C unit housing.

RECIRCULATION DOOR CABLE

Fig.18 Recirculation Door Cable:

Description
The RECIRC door is actuated by a cable which mechanically positions the door. The cable is not serviced.

Cable Adjustment
The cables must be adjusted for proper function of the control module. To adjust the cable, attach the cable to the lever arm of the control module. Turn the knob fully counterclockwise. Pull the cable jacket away from the cable end until taut. Clip the cable jacket to the control module. The knob should travel a full 180 ° if the cable is properly adjusted.