Air Conditioning Signal

To test the A/C signal, proceed as follows.

Air Conditioning Circuit:

1. Start and warm the engine to operating temperature. Turn the blower and A/C to the ON position.
2. Using a Volt meter, check the Voltage between ECU harness terminal 7 and ground.

Voltage
System Voltage.


3. Turn the key to the OFF position and disconnect the negative battery terminal and ECU connector.
4. Using an Ohm meter, check for continuity between ECU harness terminal 7 and harness terminal 1 of the A/C dual pressure switch.

Continuity
Should exist.

5. Using an Ohm meter check for continuity between ECU harness terminal 7 and ground.

Continuity
Should not exist.

NOTE: If the engine temperature is above approximately 238° F, the coolant temperature switch will open the circuit between the A/C control unit and the ECU.


If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, confirm that the repair has corrected the problem.

If the trouble returns, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.



Operation


The air conditioning switch applies battery Voltage to the engine control module when the air conditioning is switched ON.

When the air conditioning signals are input, the engine control module activates the idle air control motor, and also switches ON the power transistor. As a result, current flows to the A/C compressor clutch relay coil and the relay switch is switched ON, the air conditioning compressor's magnetic clutch is activated.


Troubleshooting Hints

If the air conditioning compressor's magnetic clutch is not activated when the air conditioning switch is switched ON during idling, it is probable that the cause is a malfunction of the air conditioning control system.




Inspection




Harness Inspection