A/C Signal: Testing and Inspection

Signals to and from A/C System, checking

Special tools and equipment
- V.A.G 1551 scan tool (or VAG 1552 mobile scan tool) with VAG 1551/3B cable
- VAG 1598/31 adapter cable
- VAG 1526 multimeter or VAG 1715 multimeter
- VAG 1594 connector test kit
- Wiring diagram

Test requirements
- The A/C system must function properly.
- A/C system must be switched off.
- There must not be any DTCs stored in DTC memory, checking DTC memory.
- Vehicle must be at room temperature (warmer than + 15 °C).

Test sequence
- Connect V.A.G 1551 scan tool (VAG 1552). Start engine and select the Engine Control Module (ECM) using address word 01. (connecting scan tool and selecting ECM). Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAG 1551 Scan Tool", Testing and Inspection

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.

Indicated on display:


Read measuring value block HELP
Enter display group number XXX


- Press buttons -0-, -5- and -0- to select "Display group number 50". Press -Q- button to confirm input.

Indicated on display: (1 to 4 = display fields)


Read measuring value block 50 ->
1 2 3 4


- Observe indication in display field 4. Compr.OFF must be indicated.
- Switch A/C system on.
- Set it to the lowest temperature and the highest fan setting.
Indication in display field 4 must switch to compr.ON.
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.

If reading does not change:







- Connect VAG 1598/31 adapter cable to control module wiring harness. Engine Control Module (ECM) is not connected.
- Check for open circuits in wires between test box socket 41 and A/C system according to wiring diagram. Wire resistance: max: 1.5 Ohms