Air Conditioning Cycling Switch PCM Inputs

A/C Cycling Switch:

Location
On top of the suction accumulator.

Function
The A/C cycling switch has the following function:
- Protecting the evaporator against icing.
- Protecting the air conditioning system against reduced pressure or an empty system.

Description
The Air Conditioning (A/C) cycling switch may be wired to either the ACCS or ACPSW PCM input. When the A/C cycling switch opens, the PCM will turn off the A/C clutch.

The A/C Cycling Switch (ACCS) circuit to the PCM provides a voltage signal which indicates when the A/C is requested. When the A/C demand switch is turned on, and both the A/C cycling switch and the high pressure contacts of the A/C high pressure switch (if equipped and in circuit) are closed, voltage is supplied to the ACCS circuit at the PCM. Refer to the applicable Wiring Diagram for vehicle specific wiring.

If the ACCS signal is not received by the PCM, the PCM circuit will not allow the A/C to operate. For additional information, refer to PCM outputs, wide open throttle air conditioning cutoff.

NOTE: The Town Car, Continental, LS6/LS8 and Windstar do not have a dedicated (separate) input to the PCM indicating that A/C is requested. This information is received by the PCM through the BUS + and BUS - (SCP) communication.

Operation
The A/C cycling switch has the function of a de-icing switch and switches the compressor clutch on/off.

The pressure and the temperature inside the suction accumulator and the evaporator are the same. If the pressure and, therefore, the temperature, drops in the suction accumulator, the temperature in the evaporator approaches freezing point. The evaporator threatens to ice up and lose its ability to cool. The A/C cycling switch then opens the compressor clutch when the pressure drops to a certain level and only closes it again when there is an appropriate rise in pressure.