A/C Signal: Testing and Inspection

NOTE:
- The A/C compressor signal communicates to the ECM that the compressor will be switched on in 140 ms.
- The ECM can switch off the A/C compressor via the same wire connection


Engine Control Module (ECM) switches off A/C compressor:
- During hard acceleration (Wide Open Throttle 1st gear)
- In emergency mode (emergency operation)
- After initiating Basic Setting (function 04)


Test conditions
- A/C system OK
- Not DTC in DTC memory of Engine Control Module (ECM)
- Vehicle at room temperature (warmer than +15 °C)

Test sequence
- Connect VAS tester or VAG 1551 scan tool and select control module for engine electronics using "address word" 01.
- Engine must run at idle for this.

When indicated on display:


Rapid data transfer HELP
Select function XX


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

When indicated on display:


Read Measuring Value Block Q
Input display group number XXX


- Press buttons -0-, -5- and -0- to select "display group number 050" and press -Q- button to confirm input.

Indicated on display. (1 - 4 = display fields)


Read Measuring Value Block 50 ->
1 2 3 4


- Switch A/C system off.
- Specified value in display field 4: Compr. OFF
- Switch A/C system on using "Auto" button and adjust A/C system to maximum cooling or heating power. Compressor must run.
- Specified value in display field 4: Compr. ON
- Fully depress accelerator pedal abruptly and then release (brief acceleration).
- Specified value in display field 4: Display switches for a few seconds from "Compr. ON" to "Corn Pr. OFF" (compressor switch - off for vehicle acceleration)

If indications do not resemble description:
- Connect VAG 1598/31 test box at wiring harness to ECM, do not connect ECM.
- Check the following wire connection for open circuit and short circuit to Ground and B+:

Test box VAG 1598/31 socket A/C control head -E87- terminal
41 -

- Repair open circuit or short circuit if necessary.
- If there are no malfunctions in the wiring, check function of A/C system.