A/C Compressor ON Signal

CHECKING A/C COMPRESSOR ON SIGNAL
The A/C compressor ON signal increases the basic value forthe Idle Air Control (IAC) valve, ensuring that idle speed remains in the center of the control map range.

- Using VAG 1551 scan tool, initiate "Read Measuring Value Block" function 08, display group 004. Refer to On-Board Diagnostics under Computers and Control Systems. Testing and Inspection

- Display will appear as shown:

Read Measuring Block Value 4
1 2 3 4

- Observe first digit of 4-digit display (switch inputs) in display field 4.
^ Specified value: OXX X

NOTE:
Switch inputs shown by digits 2 to 4 are ignored for this test.

- Switch A/C on (manual A/C) or, with automatic A/C, press buttons "AUTO", temperature "LO" and blower speed "HI."
^ Specified value: 1XX X (zero changes to one)

- Press "arrrow" button.
- Press buttons -0- and -6-to select "End Output" function 06.
- Press -Q- button to confirm input.

If the 4-digit display does not change:

- Switch ignition OFF.
- Connect VAG 1598 test box with 1598/11 adapter harness to ECM and wiring harness. Connecting VAG 1598/31 Test Box
- Connect LED tester to test box sockets 11 and 45 (Ground).
- Switch ignition ON.
- Switch A/C on as described above.
^ LED must light up

If the LED does not light up:
- Disconnect ECM harness connector C.

If LED now lights up:
- Replace ECM .

If LED does not light up:
- Check continuity of wiring and/or short circuit using wiring diagram as follows:

For manual A/C:

- Check wiring harness between ECM connector C terminal 11 and A/C switch -E30-.

For automatic A/C:

- Check wiring harness between ECM connector C terminal 11 andA/C control head -E87-.

If wiring harness is OK:
- Check A/C system.