D 250 Pickup V8-5.9L VIN Z (1992)
Air Conditioning Switch: Description and Operation
A/C SELECT SIGNAL
FUNCTION
This signal informs the engine controller 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 engine controller. If the engine
controller receives this signal as well as the A/C request input, the engine controller will energize the A/C clutch relay allowing clutch to engage.
The engine controller 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 engine controller will not receive the signal. If the signal is not received, the
engine controller will de-energize the A/C relay.
A/C REQUEST SIGNAL
FUNCTION
The engine controller monitors air conditioning evaporator temperature. If the evaporator temperature is within a specified range the engine
controller will energize the A/C relay.
OPERATION
When air conditioning has been selected by the driver, the evaporator provides an input signal to the engine controller, if the evaporator
temperature is within a specified range.
When the engine controller 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 engine controller will not receive the A/C request signal.
If the signal is not received, the engine controller will de-energize the A/C relay.
