A/C Signal: Testing and Inspection

Signal From/to Air Conditioning System, Checking

Special tools and equipment
- Scan tool VAG 1551 or vehicle system tester V.A.G 1552 with cable VAG 1551/3B
- Test box V.A.G 1598/31
- Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
- Adapter set V.A.G 1594
- Wiring diagram

Test conditions







- All fuses must be Ok
- The battery voltage must be at least 11.5 V
- All electrical consumers, e.g. lights and rear window heating must be switched off
- No DTCs must be stored in DTC memory. Refer to "Clearing Trouble Codes/With Manufacturers Scan Tool/DTC Memory Checking and Erasing" Testing and Inspection
- Air conditioner functioning OK
- Air conditioner must be switched off
- Vehicle at room temperature (warmer than +15 °C)

Test sequence
- Connect scan tool VAG 1551 (V.A.G 1552). Start engine and select "Address word" 01 of engine control module. Engine must be running at idle speed.
Connecting scan tool and selecting Engine Control Module (ECM). Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/VAG1551 Scan Tool" Testing and Inspection

Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons 0 and 8 for function "Read Measuring Value Block" and confirm entry with Q button.

Indicated on display


Read Measuring Value Block
Input display group number XXX


- Press buttons 0, 5 and 0 for "Display group number 50" and confirm entry with Q button.

Indicated on display (1-4 = Display zones)


Read Measuring Value Block 50 ->
1 2 3 4


- Check specifications for air conditioner (display zone 4)
- Observe display in display zone 4. It must show: Compr. OFF.
- Switch on air conditioning system and select lowest temperature and highest blower speed.
The display in display zone 4 must change to Compr. ON.
- Quickly floor accelerator pedal and release (brief burst of throttle).
Display zone 4 must change from Compr.ON to Compr. OFF for a few seconds (compressor switch-off when vehicle is accelerating).
- Press -> button.
- Press buttons 0 and 6 for the "End output" function and confirm input with Q button.
- Switch ignition off.

If the display does not change:
- Remove inner plenum chamber cover at left:







- Connect test box V.A.G 1598/31 to control module wiring harness. Engine control module is not connected by this action.
- 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 wiring malfunctions can be found:
- Check function of air conditioner control module.
- Check DTC memory, if necessary, repair any malfunctions and then erase DTC memory. Refer to "Clearing Trouble Codes/With Manufacturers Scan Tool/DTC Memory Checking and Erasing" Testing and Inspection
- Read readiness code. If DTC memory has been erased or engine control module was disconnected from permanent positive, readiness code must be generated again.
Refer to "Monitors, Trips and/or Drive Cycle/Readiness Code, Displaying" Testing and Inspection
Refer to "Monitors, Trips and/or Drive Cycle/Readiness Code, Generating" Testing and Inspection