Compressor HVAC: Testing and Inspection

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 wiring 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)

Requirements
- A/C system OK
- No DTCs in DTC memory of Engine Control Module (ECM).
- Vehicle at room temperature (warmer than +15 degrees C).

Work sequence
- Connect VAS5051 tester, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions and select vehicle system "01 - Engine electronics". Engine must run at idle.







Display on VAS5051:
- Select diagnostic function "08 - read measured value block" in selection -1-.







Display on VAS5051:
1 - Enter display group. Max. input value = 255
- Select function "050" in button field -2- for "display group number 050" and press Q button to confirm input.







Display on VAS5051:
- 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 accelerator pedal completely (swiftly) and then release it (brief acceleration).







Display on VAS5051:
- 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) but do not connect ECM.
- Check following wiring connection for open circuit and short circuit to Ground (GND) and B+:

Test box VAG1598/31 Socket A/C control head -E87- Terminal
41 See Electrical Wiring Diagrams, Troubleshooting & Component Locations

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