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A/C Compressor Shut-Off, Checking




A/C Compressor Shut-off, Checking


NOTE:
- The A/C compressor signal communicates to the ECM that the compressor will be switched on in 140 ms.
- The Engine Control Module (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 requirements:
- A/C system OK
- No DTCs in DTC memory of Engine Control Module (ECM).
- Vehicle at room temperature (warmer than +15 °C).

Test sequence
- Connect VAS5051 tester or VAG1551 scan tool and select control module for engine electronics using "address word". Engine must run at idle. [1][2]Scan Tool Connecting and Initial Checks

When indicated on display


Rapid data transfer HELP
Select function XX



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

When indicated on display


Read measuring value block Q
Enter 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 to 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
- Depress gas pedal completely (swiftly) and then release it (brief acceleration).
- Specified value in display field 4: Indication jumps for a few seconds from "Compr. ON" to "Compr. OFF" (compressor is switched off when vehicle accelerates).

If indications do not resemble description:
- Connect VAG1598/31 test box at wiring harness to Engine Control Module (ECM), do not connect ECM [1][2]Scan Tool Connecting and Initial Checks
- Check following wire connection for open circuit and short circuit to Ground (GND) and B+:

Test box VAG1598/31 A/C control head -E87-
Socket Terminal

41

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