A/C Signal: Description and Operation

AIR CONDITIONING CYCLING SWITCH
The Air Conditioning Cycling Switch (ACCS) is a voltage signal input to the Powertrain Control Module (PCM) which indicates when the A/C is requested. When the A/C demand switch is turned on and both the ACCS and the high pressure contacts of the A/C Pressure Switch (ACPSW) (if equipped) are closed, voltage is supplied to the ACCS circuit signal at the PCM. If the ACCS signal is not received by the PCM, the Wide Open Throttle A/C Cut-off (WAC) circuit will not allow the A/C to operate.

AIR CONDITIONING DEMAND SWITCH
The Air Conditioning Demand (ACD) switch input to the PCM is used to determine when the A/C is requested. When the A/C demand switch is turned on and the Low Pressure switch is closed the ACD circuit to the PCM is grounded. This indicates to the PCM that A/C is requested.






AIR CONDITIONING PRESSURE SENSOR
The Air Conditioning Pressure (ACP) sensor is located in the high pressure (discharge) side of the air conditioning A/C system. The ACP sensor provides a voltage signal to the Powertrain Control Module (PCM) that is proportional to the A/C head pressure. The PCM uses this information for A/C clutch control, cooling fan control and idle speed control.






AIR CONDITIONING PRESSURE SWITCH
The A/C Pressure Switch (ACPSW) is used for additional A/C system pressure control. The ACPSW is either dual function for two speed electric fan applications or single function for all others. The ACPSW is also referred to as the Refrigerant Containment Switch (single function) or Refrigerant Containment/Fan Function Switch (dual function).

For refrigerant containment control, the normally closed high pressure contacts open at a predetermined A/C head pressure. This turns off the A/C by opening the A/C demand circuit, preventing the A/C pressure from rising to a level that would open the A/C High Pressure Relief Valve.

For fan function control, the normally open medium pressure contacts close at a predetermined A/C head pressure. This grounds the ACPSW circuit input to the PCM. The PCM will then turn on the high speed fan to help reduce the pressure.

AIR CONDITIONING ON CIRCUIT
The A/C On (ACON) circuit is used by the PCM to control voltage to the A/C clutch. When the ACD input to the PCM is grounded, this indicates that A/C is requested. If the PCM determines that A/C clutch operation is desirable (i.e. engine not cranking, not at Wide Open Throttle, etc.), it will ground the ACON output. This will energize the coil of the A/C relay, close the normally open contacts and send B+ voltage to the A/C clutch. The PCM will also adjust idle speed as necessary.