Engine Speed Dips When A/C Is Switched On

ENGINE SPEED DIPS WHEN A/C IS SWITCHED ON

Preconditions
^ DTCs absent.
^ Engine is hot.
^ Fault is permanent.

Fault Sources
^ Break in signal lead from A/C compressor.
^ Defective Idle Air Control (IAC) Valve.
^ Break in signal lead from A/C relay.

TESTING PROCEDURE





Checking the A/C Relay Signal
^ START the engine and let it run at idling speed.
^ A/C button ON.
^ Blower ON.
^ Read the status of the A/C relay.

If the A/C relay is on:
- Check the A/C compressor signal.
If the A/C relay is off:
- Check the signal lead for the A/C relay.





Checking the A/C Compressor Signal
^ START the engine and let it run at idling speed.
^ A/C button ON.
^ Blower ON.
^ Read the status of the A/C compressor while the compressor is in operation.

If the A/C compressor is on:
- Check the IAC valve's connector.
If the A/C compressor is off:
- Check the signal lead for the A/C compressor.





Checking the IAC Valve's Connector
^ Clean and grease the ECM's and IAC valve's connector.
^ Check if the engine speed still dips.

If engine speed still dips:
- Test with a new IAC valve.





Checking the Signal Lead for the A/C Compressor
^ Ignition OFF.
^ Connect the break-out box and check the ground connectors.
^ Connect the ECM.
^ A/C button ON.
^ Blower ON.
^ START the engine.
^ Connect a voltmeter between #6 (ECM B6) and #28 (ECM B28) on the break-out box.
^ When the compressor operates, the voltmeter should show battery voltage.

If the value is 0K:
- The source of the dipping was contact resistance in the ECM's connector.
- Clean and grease the ECM's connector.
If the reading is incorrect:
- Check the lead between #B6 and the pressostat's coupling (7/53) connector 2 for signs of a break.





Checking the Signal Lead for the A/C Relay
^ Ignition OFF.
^ Connect the break-out box and check the ground connectors.
^ Connect the ECM.
^ A/C button ON.
^ Blower ON.
^ START the engine.
^ Connect a voltmeter between #25 (ECM B25) and #28 (ECM B28) on the break-out box.

When the compressor operates, the voltmeter should show battery voltage.

If the value is OK:
- The source of the dipping was contact resistance in the ECM's connector.
- Clean and grease the ECM's connector.
If the reading is incorrect:
- Check the lead between ECM B25 and the pressostat coupling (7/53) connector 1 for signs of a break.