A/C Signal: Testing and Inspection

A/C Compressor Shut-off, Checking

Special tools and equipment







- VAG1526A
- VAG1527B
- VAG1594A
- VAG1598/31
- VAS5051 with VAG5051/1

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

Test sequence
- Connect VAS5051 scan tool and select the control module for engine electronics using "address word" 01 . Engine must run at idle for this. Connecting VAS 5051/VAG 1551 Scan Tool (ST)

Display on VAS 5051:







- In field -1- select "08 - Read Measuring Value Block".

Display on VAS 5051:







1 - Enter display group, max. entered value = 255
- Enter "050" in field -2- to select "display group number 050" and press -Q- button to confirm input.

Display on VAS 5051:







- 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) in first gear during a road test and then release it (brief acceleration).

Display on VAS 5051:







- Specified value in display field 4: Indication jumps for several seconds from "Compr. ON" to "Compr. OFF" (compressor shut-off for vehicle acceleration)

If indications in field 4 do not resemble description:
- Connect VAG1598/31 test box at wiring harness to ECM, do not connect ECM. Electrical Testing Using VAG1598/31 Test Box
- Check the following wire connection for open circuit and short circuit to Ground (GND) and B+:

Test box V.A.G 1598/31 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.