The compressor for the air conditioning (A/C) system is driven by the engine by means of a drive belt for all engine applications. The clutch allows the compressor to disengage when the A/C is not required.
When the ignition switch is in RUN, battery voltage is supplied to the following:
| • | The HVAC control module |
| • | The A/C compressor clutch relay coil |
| • | The normally open A/C compressor clutch relay contact |
The A/C compressor clutch coil must be energized in order to drive the A/C compressor clutch. The clutch coil is energized when the clutch relay is energized. Voltage is applied from the relays contact on A/C compressor clutch control to the clutch coil. The diode in the harness is reverse-biased. The diode prevents current flow from bypassing the clutch coil to ground. When the relay coil is de-energized, the collapsing magnetic field of the clutch coil forward-biases the diode. The energy from the magnetic field dissipates
The A/C compressor clutch relay is energized when a ground path is provided for the relay coil on A/C compressor clutch relay control. The PCM/VCM provides the ground path through the module only when the module receives an A/C request signal from the HVAC module. The PCM/VCM modules may stop the A/C compressor operation while otherwise enabled under certain operating conditions as described in the powertrain engine controls sections.
When the PCM/VCM receives the A/C request signal from the HVAC module through A/C high pressure cutout switch feed through the A/C high pressure cutout switch and A/C request signal (PCM/VCM), the PCM/VCM will source circuit 459 to ground. This closes the relay contact and supplies battery voltage to the A/C compressor clutch coil. The A/C compressor high pressure cutout switch, located at the rear of the compressor, monitors the compressor high side pressure. When this pressure exceeds a preset limit, the switch contacts open in order to interrupt the request signal from the HVAC module. The A/C compressor disengages. The A/C low pressure cycling switch monitors evaporator low side pressure in order to provide freeze-up protection. When the low side pressure reaches a preset limit, the switch contacts open. The PCM/VCM monitor the open contacts. The ground to the A/C relay is removed. The A/C compressor disengages. When the pressure recovers, the low pressure switch contacts close. The normal operation of the A/C compressor resumes.
The A/C automatic recirculating switch is a secondary high pressure switch, located at the lower right front of the A/C condenser, that will close when high side pressure is detected. The PCM/VCM monitors this switch operation. The PCM/VCM will place the A/C air delivery system in a recirculating mode until the high side pressure returns to normal.
The HVAC control module consists of the following components:
| • | A 6 way blower switch |
| • | A rotary air delivery switch |
| • | An air mix rotary control switch |
| • | An air source discrete push buttons that select between outside and recirculated air |
| • | An A/C compressor discrete request button and a rear defrost discrete push button with a built in timer |
The HVAC control module also has LEDs (light emitting diodes) for the A/C request and defrost that will illuminate when selected.
