Compressor HVAC: Testing and Inspection

Operational Description

Control Unit Circuit:

The compressor control unit has a system designed to protect the compressor belt in the event of a seizure, thereby allowing the alternator to continue operating.

This is done by comparing the engine rpm and the compressor pulley rpm. When there is a difference in rpm that continues for more than 3 seconds, the compressor relays are turned off and the warning light comes on.

To reset, push the A/C switch off, then push it on again.

NOTE: If the switch is pushed off and on more than twice, it will be necessary to turn off the ignition to reset.

Compressor Input Test

Control Unit Circuit:

Connector View:

Perform the initial tests in the illustration below with the A/C control unit disconnected, and the ignition switch, blower switch, and A/C switch ON.

Input Test:

NOTE:
- Make sure all connectors are clean and tight.
- Make all tests from the wire side of the connector with a digital multi-tester.
- Any abnormality found during these tests must be corrected before continuing.
If all tests produce the desired results, substitute a known-good control unit and retest.