Checking signals from/to air conditioner: VW 2.8 TDI (AUH, BCQ)

Special tools, workshop equipment, test and measuring equipment and accessories required

Fault output device V.A.G 1551 using cable V.A.G 1551/5
Testing box V.A.G 1598/30
Hand-held multimeter V.A.G 1526 or Multimeter V.A.G 1715
Measuring aids set V.A.G 1594
Current flow diagram

Testing conditions

The air conditioner must function properly.
No fault must be stored in the fault memory =>page
01-10
, retrieve fault memory.
The vehicle must be at room temperature (warmer than + 15 °C).
Air conditioner switched on

Check compressor shut-off

Via the signal that the air conditioner is ready, the engine control unit receives the information that the air conditioner compressor will be switched on.

during strong acceleration in1st gear
for refrigerant temperatures above + 120°C
following each starting process for approx. 6 sec.

Testing Procedure

Connect the fault output device V.A.G 1551 (V.A.G 1552) and use the "Address word" 01 to select the control unit for engine electronics. Here, the engine must be idling.
(Connecting fault reader and selecting engine electronics control unit => page
01-4
.)

Fast data interchange
HELP
Select function XX
Display:

Press the keys 0 and 3 for the function "Diagnosis of actuators".

Fast data interchange
Q
030303 diagnosis of actuators
Display:

Confirm the input using the Q key.

Final control diagnosis
⇒
Air-conditioner compressor intervention
Display:

The air-conditioner compressor deactivation is checked.
The air conditioning compressor must come to a halt within 5 seconds (visual check), and then start up and come to a halt again approx. every 5 seconds.

If the air conditioning compressor is not deactivated:

Complete the final control diagnosis.
Press the keys 0 and 6 for the function "Quit data interchange" and confirm the input using the Q key.
Switch the ignition off.

Connect the testing box V.A.G 1598/30 to the control unit wiring loom. The engine control unit is not connected in the process.
Check for breaks in the cable between the test box socket 4/19 and the air conditioner in accordance with the current flow diagram.
Cable resistance: max. 1.5 ω

=> Folder Current Flow Diagrams, Electrical Fault Finding and Fitting Locations