Signal From/to A/C Compressor, Checking

Required special tools and test equipment
- VAG 1551 or VAG 1552 Scan Tool (ST) with VAG 1551/3 adapter cable
- VAG 1598/22 test box
- Multimeter US 1119 (Fluke 83 or equivalent)
- VW 1594 connector test kit
- Wiring diagrams

Test conditions
- A/C functions OK
- A/C is switched off
- Vehicle at room temperature-above 15 °C (59 °F)
- No malfunctions stored in Diagnostic Trouble Code (DTC). Refer to "Check Diagnostic Trouble Code (DTC) Memory (Function 02)"

Checking
- Connect VAG 1551 or VAG 1552 scan tool and press buttons -0- and -1- to insert "Engine Electronics" address word 01 (with engine running at idle).

Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08, and press -Q- button to confirm input.

Indicated on display


Rapid Measuring Value Block HELP
Input display group number XXX


- Press buttons -0-, -5- and -0- to input display group number 50, and press -Q- button to confirm input.

Indicated on display (1-4 = display fields)


Read Measuring Value Block 50 ->
1 2 3 4


- Switch on A/C (lowest temperature and highest fan position).
- Compare display with specified value in display fields 4.

Display Group 50:

NOTE:
- The A/C compressor is switched off during acceleration when the car is stationary or at slow speed.
- At wide open throttle the A/C compressor is switched off by the Transmission Control Module (TCM) (kick down switch).


Continuation
If the displayed values are NOT OK:
- Connect VAG 1598/22 test box to ECM harness connector.
- Check wiring for open circuit, short circuit to B+ or short circuit to Ground between ECM/test box terminal 8 and A/C control head -E87-, or Transmission Control Module (TCM).

If the wiring is OK:
- Check function of A/C control head -E87-.
- Check readiness code. If Diagnostic Trouble Code (DTC) memory has been erased, or ECM was disconnected, generate new readiness code.