A/C Signal: Testing and Inspection
Signal From/To Air Conditioning System, Checking
Special tools and equipment
- V.A.G 1551 scan tool or 1552 scan tool with cable VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram
Test conditions
- Air conditioner functioning OK.
- Air conditioner must be switched off
- No faults must be stored in DTC memory Reading Diagnostic Trouble Codes
- Vehicle at room temperature (warmer than +15°C).
Test sequence
- Connect V.A.G 1551 scan tool ((VAG 1552). Start engine and select "Address word" 01 of engine control module. When doing this the engine must be running at idling speed.
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press keys 0 and 8 for the function "Read measuring value block" and confirm entry with Q key.
Indicated on display:
Read measuring value block
Input display group number XXX
- Press keys 0, 5 and 0 for "Display group number 50" and confirm entry with Q key.
Indicated on display: (1 to 4 = Display zones)
Read measuring value block 50 ->
1 2 3 4
- Observe display in display zone 4. It must show
Compr. OFF.
- Switch on air conditioning system.
- Select lowest temperature and highest blower speed.
The display in display zone 4 must change to
Compr. ON.
- Floor accelerator pedal quickly and then release (brief burst of throttle).
The display in display zone 4 must change from
Compr.ON
to
Compr. OFF
for a few seconds (compressor switch-off when vehicle is accelerating).
- Press the -> key.
- Press keys 0 and 6 for the "End output" function and confirm input with the Q key.
- Switch off ignition.
If the display does not change:
- Remove wiper arms and cowl panel
- Connect test box VAG 1598/31 to control module wiring harness. The engine control module remains disconnected.
- Check wiring for open circuit between test box sockets 40 + 41 and air conditioner system using wiring diagram.
Wire resistance: max. 1.5 Ohms
If no fault can be found in the wiring:
- Check function of air conditioner control module.
- Check DTC memory, if necessary, repair any faults and then erase DTC memory