Air Conditioning System Signal, Checking

Signals to and From A/C System, Checking

Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- All fuses must be OK.
- The A/C system must function properly.
- A/C system must be switched off.
- There must not be any DTCs stored in DTC memory.
- All electrical consumers like, for example, lights and rear window heating must be switched off.
- Battery voltage must be at least 11.5 volts.
- Vehicle must be at room temperature (warmer than +15 °C).

Test sequence
- Connect VAG1551 scan tool (VAG1552). 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 " 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
Enter display group number XXX


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

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


Read measuring value block 50 ->
1 2 3 4

Display Group 50:

- Check specified values for A/C system (display fields 3 and 4)
- Observe reading in display field 4. Compr. OFF should be displayed.
- Switch A/C system on.
- Set it to the lowest temperature and the highest fan setting.
The reading in display field 3 should change to A/C-High.
The reading in display field 4 should change to Compr. ON.
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.

Continuation

If reading does not change:







- Connect VAG1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.
- Check wires between test box sockets 40 + 41 and A/C system for open circuits according to wiring diagram. Wire resistance: max: 1.5 Ohms

If there is no malfunction in wire connection:
- Check function of A/C control head.