A/C Signal: Testing and Inspection
A/C Compressor (On/Off Signal), Checking
A/C compressor ON signal
Voltage is supplied to the engine control module shortly before switching on the air conditioner compressor. The signal ensures that the control module keeps the idling speed constant for the differing power requirements of the air conditioning system.
A/C compressor OFF signal
The air conditioner compressor is switched off for approx. 12 seconds by the engine control module when accelerating from a standstill and from low speeds to ensure that the full engine power is available. If the accelerator is released earlier the time is shortened to a minimum of 3 seconds. At wide open throttle the air conditioner is switched off by the transmission control module (kick down switch).
Special tools and equipment
- VAG 1551/1552 Scan Tool using VAG. 1551/3 adapter cable
- VAG 1598/18 Test Box
- Fluke 83 multimeter (or equivalent)
- VW 1594 Adapter kit
- Wiring diagram
Test conditions
- A/C functions OK
- A/C switched off
- Vehicle interior temperature: 15 °C (59 °F) minimum
- No malfunctions (DTC's) stored in DTC memory.
Test sequence
- Connect VAG 1551 (VAG 1552) Scan Tool. Refer to Scan Tool Testing/VAG 1551 Scan Tool. Testing and Inspection
- With engine idling, press buttons -0- and -1- to select "Engine Electronics" address word 01.
Display will appear as shown
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read measuring value block".
- Press -Q- button to enter selection.
Display will appear as shown
Read measuring value block HELP
Input display group number XXX
- Press buttons -0-, -0- and -8- to select "Display group number 8".
- Press -Q- button to enter selection.
Display will appear as shown (1 to 4 = Display fields)
Read measuring value block 8 ->
1 2 3 4
- Check A/C specifications (Display fields 3 and 4).
Display Group 8:
- Observe display in field 4.
- Display must show "Compr. OFF"
- Switch on A/C and select lowest temperature and highest blower speed.
- Display in field 4 must change to "Compr. ON"
- Press buttons -0- and -6- to select "End output" and confirm input with -Q- button.
- Switch ignition off.
Continuation
If display does not appear as described.
- Connect VAG 1598/18 Test Box to ECM wiring harness.
- Check wiring (for A/C open circuit) between Test Box sockets 37 and 39 respectively using wiring diagram.
- wire resistance: 1.5 Ohms maximum
If specification not obtained:
- Check wiring using wiring diagram
If wiring OK:
- Check function of air conditioner control module
- Read-out Readiness code. Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Readiness Code Checking. Testing and Inspection
If DTC memory has been erased:
- Create Readiness code. Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Readiness Code Generating Testing and Inspection