A/C Signal: Testing and Inspection
Notes:
^ The A/C ON signal increases the basic idle speed to approx. 800 rpm.
^ The A/C compressor ON signal increases the basic value for the Idle Air Control (IAC) valve, ensuring that the IAC valve remains in the center range of the control map.
^ The A/C compressor cut-out signal switches OFF the A/C compressor for approximately 3 to 12 seconds, when the vehicle is accelerated from a standing start or a low speed.
Requirements
^ A/C function OK
^ No malfunctions stored in Diagnostic Trouble Code (DTC) Memory
^ Vehicle at room temperature, i.e. warmer than 15°C (59°F)
Procedure
- Connect VAG 1551 scan tool. Refer to Connecting and Operating VAG 1551 Scan Tool Connecting and Operating VAG 1551 Scan Tool
- Advance through program until display appears as shown:
Rapid data transfer HELP
Select function XX
- Let engine idle.
- Press 0 and 8 buttons to select function 08 "Read Measuring Block Value"
- Display will appear as shown:
Rapid data transfer Q
08 Read Measuring Block Value
- Press Q button to enter input
- If display appear as shown:
Rapid data transfer HELP
Input display group number XXX
- Be sure A/C is switched OFF.
- Start engine and let idle.
- Input display group number 05.
- Observe display values in channel 4.
Display position 1 indicates if A/C compressor is ON or OFF:
^ Must read 0, A/C Compressor OFF
Display position 2 indicates if A/C system is ON or OFF:
^ Must read 0, A/C system OFF
Display position 3:
^ Must remain blank
- Switch ON the A/C, selecting lowest temperature and highest blower speed.
- Observe display values.
^ Position 1 must change from 0 to 1
^ Position 2 must change from 0 to 1
- Observe display while performing the following:
- Press accelerator pedal to floor quickly, then release immediately.
^ Position 1 must change from 1 to 0, for several seconds
If display position 1 does not change:
- Connect VAG 1598 Test Box, using VAG 1598/5 adapter cable, to ECM. Refer to VAG 1598 Pin Out Box Connecting and Testing. Connecting and Testing VAG 1598 Pin Out Box
- Connect US 1115 LED tester or equivalent between terminal 19 (GND) and terminal 6.
- Allow engine to idle.
- Switch ON A/C, selecting lowest temperature/highest blower speed.
^ LED tester must light up, within 1-6 seconds
- Apply accelerator pedal quickly, then release immediately.
^ LED tester must go out for a few seconds
If NO (for either step):
- Switch ignition OFF (stop engine).
- Wait at least 30 seconds before disconnecting adapter cable from ECM.
- Check wiring for breaks/opens between ECM terminal 6 (terminal 6 of Test Box), and A/C control head terminal C12, using wiring diagram.
If wiring OK:
- Check function of A/C clutch control module - J153.
- Check function of A/C control head - E87.
If A/C control module and A/C control head are OK:
- Replace ECM.
If display position 2 does not change:
- Connect VAG 1598 Test Box, using VAG 1598/5 adapter cable, to ECM. Refer to VAG 1598 Pin Out Box Connecting and Testing. Connecting and Testing VAG 1598 Pin Out Box
- Connect US 1115 LED tester or equivalent between terminal 19 (GND) and test box terminal 41 (ECM terminal 41).
- Allow engine to idle.
- Switch ON A/C, selecting lowest temperature/highest blower speed.
^ LED tester must light up.
If NO:
- Switch ignition OFF (stop engine).
- Wait at least 30 seconds before disconnecting adapter cable from ECM.
- Check wiring for breaks/opens between ECM terminal 41 (terminal 41 of Test Box), and A/C control head terminal A2, using wiring diagram.
If wiring OK:
- Check function of A/C
If A/C function is OK:
- Replace ECM.