A/C (Cars Without ETS)

FAULT DIAGNOSIS, A/C (cars without ETS)

Fault Symptom.
The A/C compressor does not work.


Conditions.
For the Trionic system to activate the A/C system, the engine must have been started and the pressure sensor and throttle position sensor must be OK.

Functions / Definitions
Information to the effect that the compressor and fan must be switched on ('AC-REQUEST') is obtained via pin 59 of the Trionic control module.

The control module prepares for this increase in engine load by opening the IAC valve slightly. Following this, the Trionic control module grounds the A/C relay (via pin 54). The A/C relay in its turn controls the compressor and fan ("AC OUT" or AC-RELAY").


DIAGNOSTIC PROCEDURE

1. Checking The A/C Request Function
Connect the Scan Tool.
Start the engine.
Communicate with the Trionic system.
Select "READ ON/OFF".
Select "AC REQUEST".
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 sent to the Trionic system.
The Scan Tool should show ON and engine rpm should increase.

If these conditions are fulfilled, continue with point 2.

If these conditions are not fulfilled, the fault is located before the Trionic system (between the A/C button or the ACC control module and pin 59).






2. Checking The A/C Relay
Engine switched off.
Ignition switch in the ON position.
Select "ACTIVATE".
Select "AC RELAY".
The sound of the A/C relay and the compressor starting should now be heard.

If these conditions are fulfilled, continue with point 3.

If these conditions are not fulfilled, the fault is located after the Trionic system (i.e. between pin 54 and the compressor/fan).


3. Checking The IAC Valve
Fit an IAC valve that is known to be OK.
Check that the engine works faultlessly on engagement of the A/C.

If engine speed still drops, continue with point 4.

If engine speed does not drop, change the IAC valve.

4. Checking Operation Of The A/C
Drive the car on test and check whether the fault symptoms persist.

If the symptoms persist, refer to Before Replacing A Control Module.

If the symptoms have gone, the action taken to rectify the fault was correct, otherwise the fault is of intermittent nature.