A/C Compressor Fails To Engage

Symptom Of Fault.
The A/C compressor clutch does not engage.

Conditions.
No diagnostic trouble codes. For the Trionic system to activate the A/C compressor, the engine must have been started. The pressure sensor and throttle position sensor must also be in perfect working order.

Functions/Definitions.
Information to the effect that the compressor is to be engaged ("A/C IN") is received by the Trionic control module on pin 59. The control module prepares for this imminent load increase by opening the idle air control valve slightly. Via pin 54 the Trionic control module then grounds the A/C relay, which in its turn controls the A/C compressor ("A/C OUT" or "A/C RELAY").





Diagnostic Procedure.
1. Check the A/C request ("AC IN")
- Connect an ISAT scan tool.
- Start the engine.
- Contact the Trionic system.
- Select "READ ON/OFF".
- Select "A/C IN".
- Activate the compressor from the dashboard:
^ Manual A/C: fan ON and A/C button depressed. '
^ ACC: select AUTO.
Note that the antifrost thermostat periodically breaks the signal between the EDU and the Trionic system.
The ISAT scan tool should show "ON" and engine speed should increase slightly.

Conditions fulfilled?
YES:
^ Continue with point 2.
NO:
^ The fault is situated before the Trionic system (between the A/C button or ACC control module and pin 59). Continue fault diagnosis in the Climate control system, ACC and Electrical system, A/C-ACC.

NOTE: If the engine coolant temperature is too high or in the event of an incorrect coolant temperature sensor signal to the EDU, the EDU will break the A/C circuit.





2. Check the A/C relay ("AC OUT")
- Engine switched off.
- Ignition switch in ON position.
- Select "ACTIVATE".
- Select "A/C RELAY".
The A/C relay and the compressor clutch should now both be heard.

Conditions fulfilled?
YES:
^ No electrical fault present.
NO:
^ The fault is probably after Trionic (i.e. between pin 54 and the compressor). Continue fault diagnosis in the Climate control system, ACC. If no fault can be found, continue at "Before Replacing a Control Module". Component Tests and General Diagnostics