HVAC Compressor Controls Circuit Description

The compressor for the air conditioning (A/C) system is driven by the engine through the following components:
- The belt drive
- The A/C compressor clutch.

Battery voltage is supplied to mode switch of the heater and A/C controller through HVAC fuse 9 and CKT 141 (BRN) when the ignition switch is turned to the RUN position.
An A/C request signal is provided when one of the following A/C functions is selected:
- MAX
- NORM
- BI-LEVEL
- BLEND
- DEF

The A/C request signal is monitored by the control module. The 2.2L engine utilizes a powertrain control module (PCM) and the 4.3L engine a vehicle control module (VCM).

The A/C request signal for the PCM is provided by CKT 203 (LT BLU) from the heater and A/C controller. The PCM monitors system pressure signals supplied by the A/C refrigerant pressure sensor. The signal is used to maintain the proper engine idle and to delivery fault codes when necessary.

The A/C request signal for the VCM has the following route:
1. CKT 203 (LT BLU) to the A/C compressor high pressure cutoff switch
2. The A/C compressor high pressure cutoff switch to CKT 762 (DK GRN/WHT) to the vehicle control module (VCM).

The VCM monitors the A/C compressor cycling switch in the system through CKT 603 (DK GRN). The VCM disables the A/C operation if the pressure drops below a predetermined level. The VCM will also monitor the systems high pressure. A/C system will be disabled if the system pressure rises above a predetermined level.

The control module (PCM/VCM) supplies the ground path for the A/C compressor clutch relay coil and CKT 459 (DK GRN/WHT) when the A/C request signal is received. Voltage is provided by the IGN-E fuse. With the relay energized the contacts will close and complete the current path for the compressor. Current path is provided via the following components:
1. A/C fuse
2. A/C compressor clutch relay
3. CKT59(DK GRN)
4. A/C compressor clutch
5. CKT 350 (BLK)

The A/C compressor clutch diode is connected across the A/C compressor coil for circuit protection.