A/C Signal: Testing and Inspection
Signal from/to Air Conditioning System, Checking
Special tools and equipment required
- Scan tool VAG 1551 or vehicle system tester VAG 1552 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 fault memory, interrogating fault memory. Refer to "Displaying, Reading and Erasing Trouble Codes" Testing and Inspection
- Vehicle at room temperature (warmer than + 15 °C).
Test sequence
- Connect scan tool VAG 1551 (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 measured value block" and confirm entry with Q key.
Indicated on display:
Read measured value block HELP
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: (1-4 = Display zones)
Read measured 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 -> key.
- Press keys 0 and 6 for "End output" function and confirm input with Q key.
- Switch off ignition.
If the display does not change:
- 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