A/C Signal: Testing and Inspection

Air Conditioner Compressor Shut-off, Testing

NOTE:
- The air conditioner compressor signal informs the engine control module that the compressor will be switched on in 140 ms.
- The engine control module can send a signal via the same wire to shut off the air conditioner compressor.
- The engine control module will shut off the air conditioner compressor in the following circumstances:
- Under heavy acceleration (full throttle in 1st gear)
- In emergency running mode (back-up)
- When the "Basic setting" function is started (function 04)

Requirements for test:
- Air conditioner okay
- No faults stored in Diagnostic Trouble Code (DTC) memory of engine control module Vehicle at room temperature (above + 15 degree C)

Test sequence
- Connect the vehicle diagnostic, testing and information system VAS 5051, and select the vehicle system "01 - Engine electronics" from the menu. When doing this the engine should be idling. Connecting VAS 5051/VAG1551 Scan Tool






Display on VAS 5051:
- Select the diagnosis function "08 - Read data block" from the menu -1-.






Display on VAS 5051:
1 - Enter display group
(figures up to 255)
- Using the keypad -2-, enter "050" to select Display group 050 and confirm entry with Q button.






Display on VAS 5051:
- Switch off air conditioner.
- Specification for display zone -4-: "Compr.OFF"
- Switch on air conditioner by pressing "AUTO" key and select maximum warm or cold air setting. The compressor should run.
- Specification for display zone -4-: "Compr. ON"
- Floor and release the accelerator quickly (short blip).






Display on VAS 5051:
- Specification for display zone -4-: the display should change from "Compr.ON" to "Compr.OFF" for a few seconds (air conditioner compressor shut-off during acceleration).

If the readout in display zone 4 is not as described:
- Connect test box VAG 1598/31 to wiring harness for engine control module. Do not connect to the engine control module itself. Wiring and Component Testing Using VAG1598/31 Test Box
- Test for open circuit and short to positive or Ground in the following wiring connection:

- Test box VAG 1598/31 Socket - 41 (AC operating and display unit -E87

- Correct short circuit or open circuit if necessary.
- If there are no malfunctions in the wiring, test operation of air conditioner.