Grand Cherokee 4WD V8-318 5.2L VIN Y MFI (1994)
Air Conditioning Switch: Description and Operation
A/C SELECT SIGNAL
FUNCTION
This signal informs the PCM that the air conditioning has been selected.
OPERATION
When the A/C switch is activated by the driver, and the A/C low pressure switch is closed, a signal is sent to the PCM. If the PCM receives this
signal as well as the A/C request input, the PCM will energize the A/C clutch relay allowing clutch to engage.
The PCM also sends output signals to the Automatic Idle Speed (AIS) motor to raise the idle speed to a predetermined rpm to compensate for the
additional load placed upon the engine.
If the A/C low pressure switch opens, indicating low Freon level, the PCM will not receive the signal. If the signal is not received, the PCM will
de-energize the A/C relay.
A/C REQUEST SIGNAL
FUNCTION
The PCM monitors air conditioning evaporator temperature. If the evaporator temperature is within a specified range the PCM will energize the
A/C relay.
OPERATION
When air conditioning has been selected by the driver, the evaporator provides an input signal to the PCM, if the evaporator temperature is within
a specified range.
When the PCM receives this input, it energizes the A/C relay, so that the A/C clutch can be engaged. Also, a signal is sent to the AIS motor to
raise the idle speed to compensate for the additional load placed upon the engine.
If the evaporator is not at the proper temperature, the evaporator switch will open and the PCM will not receive the A/C request signal. If the
signal is not received, the PCM will de-energize the A/C relay.
