Automatic Temperature Control System (ATC)

A. T. C. System Self-Diagnosis

^ Ensure that the Venturi tube for the in-vehicle sensor is clear of debris and is not kinked. Be sure it is connected to the heater case and in-vehicle sensor. Check for proper air flow past the in-vehicle sensor.

^ Perform the A.T.C. self-diagnosis test

Note:
Actual temperature readings should be taken at the intake air temperature sensor, ambient temperature sensor, and in-vehicle sensor. Compare them to values given by the system. A difference of more than 5 degrees F indicates a faulty sensor that should be replaced.

A.T.C. Function Test

Perform the following operational checks of the A.T.C. system:

^ Confirm that the air outlets change over properly.

^ Confirm that the blower motor speeds and air velocity both change with operation of controls.

^ Confirm that the discharge air temperature changes when required.

^ Confirm that the Fresh air / Recirc. air door changes position correctly.

^ Check and note the setting of the A.T.C. Auxiliary mechanism: Temperature setting trimmer. DO NOT change the trimmer setting at this point in the procedure.