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 1551/3 cable
- VAG 1598/31 test box
- 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, Check DTC memory.
- Vehicle must be at room temperature (warmer than +15°C).

Test sequence

- Connect V.A.G 1551 scan tool (V.A.G 1552). Start engine and select Engine Control Module (ECM) using address word 01.

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
Input display group number XXX

- Press 0, 5 and 0 for function "display group number 50", and then press Q to exit from input mode.

Indicated on display (1 - 4 = display fields)

Read Measuring Value Block 50 ->
1 2 3 4

- Observe reading in display field 4.
- Switch A/C system on.
- Set it to lowest temperature and highest fan setting. Reading in display field 4 should change to: Compr.ON
- Suddenly press accelerator pedal to wide open throttle and then release it (brief acceleration).

The reading in display field 4 should change from
Compr.ON (for a few seconds to)
Compr. OFF (compressor is switched off when vehicle accelerates).

- 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 V.A.G 1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.
- Check for breaks in wires between test box sockets 40 + 41 and A/C system (see wiring diagram).

Wire resistance: max. 1.5 Ohms