A/C Controls

A/C CONTROLS

Fig. 1 Compressor Clutch - Typical:

A/C 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 keyed to the compressor shaft and secured with a nut. These components provide 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.

DUAL PRESSURE CUT-OFF SWITCH
The Dual Pressure Cut-Off (DPCO) Switch monitors the refrigerant gas pressure in the A/C system. The DPCO is located on the filter-drier.

Whenever the pressure drops below 196 to 248 kPa (28.4 to 36 psi) or exceeds 2544 to 3137 kPa (369 to 455 psi) (which could damage the compressor), the DPCO will open. The A/C switch sense circuit will open to the HVAC control causing the PCM to turn OFF the compressor clutch relay. The DPCO is a non-repairable, sealed factory calibrated unit, and must be replaced if defective.

BLOWER MOTOR RESISTOR BLOCK
The blower motor resistor is located in the engine compartment on the bottom side of the blower motor housing. It is secured with a screw to the blower motor housing, and is connected to the blower motor wire harness.

The resistor has multiple resistor wires, each of which reduce the current flow to the blower motor, to change the blower motor speed. The blower motor switch directs the electrical current through the correct resistor wire to obtain the selected blower motor speed.

The resistor can be removed without having to remove the blower motor housing from the vehicle.

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