A/C Signal: Testing and Inspection
A/C compressor signal, checking
A/C compressor signal:
Voltage is supplied to the ECM shortly before switching on the A/C compressor. This signal ensures that the ECM keeps the idle speed constant for the differing power requirements of the A/C system.
A/C cut-off:
The A/C compressor is switched OFF for approx. 12 seconds by the ECM when accelerating from standstill and from low speeds to ensure that full engine power is available during acceleration. If the Throttle is released earlier; the time period is shortened to a minimum of 3 seconds. At Wide Open Throttle the A/C is switched OFF by the Transmission Control Module via the kick-down switch.
Special tools, workshop equipment, testers, measuring instruments and auxiliary items required
- VAG 1551/1552 Scan Tool using VAG 1551/3 Adaptor cable
- VAG 1598/22 Test Box
- Fluke 83 multimeter
- VW 1594 Adaptor kit
- Wiring diagram
Requirements
- A/C functioning OK.
- A/C must be switched OFF, if installed
- No malfunctions stored in DTC memory.
- Vehicle at room temperature (+ 15 °C minimum (59 °F))
Test sequence
- Connect VAG 1551/1552 Scan Tool. Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks", Testing and Inspection
- Start engine and let idle
- Press 0 and 1 buttons to select "Engine Electronics" address word 01.
Indicated on display (example only)
06A906018AB Motronic M5.9.2 HS V06 ->
Coding 00000 WSC 00000
- Press -> button.
Indicated on display
Rapid data transfer HELP
Select function XX
- Press 0 and 8 buttons to select "Read Measuring Value Block" function 08.
- Press Q button to enter input.
Indicated on display
Read measuring value block
Input Display group number XXX
- Press 0, 5 and 0 buttons to select "Display group 50"
- Press Q button to enter input.
- Observe display in Display field 4. it must show Compr. OFF
- Switch ON A/C system.
- Select lowest temperature and highest blower speed
- display in field 4 must change to: Compr. ON
Indicated on display (1 to 4 = Display fields)
Read measuring value block 50 ->
1 2 3 4
- Check A/C specifications (Display fields 3 and 4)
- Quickly depress and release accelerator pedal (short throttle burst).
- After quickly depressing pedal, display field 4 must change from "ON" to "OFF" for a few seconds (A/C compressor cut-off for vehicle acceleration).
- Press -> button.
Indicated on display
Rapid data transfer HELP
Select function XX
- Press 0 and 6 buttons to select Function 06: "End output"
- Press Q button to enter input.
- Switch OFF ignition.
NOTE: The A/C compressor will be switched OFF (Compr. OFF) when the Engine Control Module recognizes Wide Open Throttle and the A/C is switched ON (A/C-HIGH).
If display does not appear as described:
- Connect VAG 1598/22 Test Box to ECM wiring harness.
- Check wiring for open circuit between Test Box socket 8 and A/C using Wiring diagram (> 1999).
- Check wiring for open circuit between Test Box socket 10 (2000 >) and A/C using Wiring diagram.
- Wire resistance: 1.5 Ohms maximum
If wiring OK:
- Check A/C Control Module function
- Display the Readiness code. Refer to "Monitors, Trips and/or Drive Cycle (Readiness Codes)/Displaying Readiness Code", Testing and Inspection
- If DTC memory was erased or if the ECM was disconnected from Battery + , set the Readiness code. Refer to "Monitors, Trips and/or Drive Cycle (Readiness Codes)/Setting Readiness Code", Testing and Inspection