Control Assembly: Description and Operation

A/C Control Assembly Faceplate:

System Operation:

DESCRIPTION

The electronic A/C control assembly has soft-touch switches for selecting operating mode(s) and the desired in-car (set) temperature. LED indicators light to show which modes have been selected, and a Vacuum-fluorescent (VF) display shows the outside air temperature (when selected), the set temperature, or a diagnostic code, which can identify a fault within the system.

OPERATION

The control assembly contains a microprocessor which receives signal information from sources such as the control panel switches, temperature sensors, and the temperature valve feedback potentiometer in the programmer. In turn, the microprocessor sends command signals to the programmer to position the air valves and to the blower motor control module to control the blower speed. This enables the system to maintain a set in-car temperature of 65°F to 85°F.

Diagnostic Switch:

Microprocessor

The microprocessor retains the operating mode, blower mode, and temperature settings when the Ignition is turned off. They are retained for up to 30 minutes, after which, when the ignition is turned on, the microprocessor will reset to the AUTO-AUTO operating and blower modes; the previously set temperature will still be retained.

An additional function of the microprocessor is that of system self-diagnosis. Faults in the temperature sensor circuits and temperature valve control circuit are identified when the A/C control assembly is set to the diagnostic mode. Diagnostic codes are displayed on the VF display. If the system does not have an identifiable fault, a 00 code will be displayed. Diagnostic mode activation and fault code identification are fully described under Air Door Actuators. Refer to Air Door Actuators / System Diagnosis / Procedures / Delivery and Temperature Controls. Testing and Inspection