Air Conditioning Signals, Checking

NOTES:
- When A/C is switched on, Engine Control Module (ECM) terminal C14 receives a positive (+) voltage signal.


Test conditions
- Vehicle at room temperature, greater than 15 °C (59 °F)
- No A/C malfunctions stored in DTC memory
- Engine Coolant Temperature (ECT) at least 85 °C (185 °F)
- ECM coding OK
- Transmission selector lever in Neutral position
- Rear window defogger switched off

- Connect VAG 1551 (VAG 1552) Scan Tool (ST) and press buttons -0- and -1- to insert "Engine Electronics" address word 01 (engine running at idle). [1][2]Scan Tool Connecting and Initial Checks

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


Read Measuring Value Block
Input display group number XXX


- Press buttons -0-, -2- and -1- to input display group number 21, and press -Q- button to confirm input.

Indicated on display


Read Measuring Value Block 21 ->
1 2 3 4


- Check specified values for A/C operating conditions (display fields 2 and 3):







- Switch A/C on; press "Auto" button; set "-" or "+" buttons for maximum heating, or maximum cooling, as specified.
- Specified value in display field 2: A/C-High
- Specified value in display field 3: Compr. on

If specified values are not displayed:
- Stop engine (switch ignition off).
- Connect VAG 1598/19 test box to ECM harness connector. Connecting VAG 1598/19 Test Box
- Connect VAG 1527 LED voltage tester between ECM/test box sockets C14 and D11 (Ground).
- Switch ignition on.
- Switch A/C on.
LED must light up.

If LED does not light:







- Check wiring for open or short circuit between ECM/test box socket C14 and A/C control head -E87-.
See Electrical Wiring Diagrams, Troubleshooting and Component Locations.

If wiring and connections are OK:
- Check function of A/C control head.