A/C Signal: Testing and Inspection

NOTE: A number of problems, in addition of a defective A/C switch, can cause A/C system malfunctions. For complete diagnosis and repair information on the air conditioning system, refer to HEATING, VENTILATION AND AIR CONDITIONING.

1. With engine at operating temperature and running at idle, probe ECM terminal M1-20 (green wire) with positive voltmeter lead and ground negative lead.
2. Turn A/C switch "ON." Meter should read battery voltage, indicating that switch is functioning properly and A/C request signal is reaching the ECM.
3. If problems are indicated, check circuits and the switch itself as described in step four below.
4. To check switch separately, remove from vehicle and connect an ohmmeter across switch terminals. With switch "OFF," meter should indicate an open circuit. With switch "ON," meter should indicate continuity.