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Wednesday, November 21, 2007

Tech Tip Fix: Volkswagen A/C Clutch Control Testing Manual A/C Systems using Fan Control Modules with 14 Pin and 4 Pin Connection Connectors

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Volkswagen A/C Clutch Control Testing Manual A/C Systems using Fan Control Modules with 14 pin and 4 pin connection connectors

by Jim Newkirk, WORLDPAC Assist European Team Leader

In this example a 2002 Volkswagen Beetle 2.0L AVH with manual climate control was experiencing two separate problems.

  • The Air Conditioning Compressor Clutch would not engage

  • The Cooling Fans would not operate at any speed

  • Diagnostic Procedures:

    1. When the A/C is switched on (the blower motor must also be running at any speed) check for 12 volts from the A/C switch in the dash to the fan control module pin T14/8.

      NOTE: Cooling fans should run at low speed whenever the A/C is switched on.

    2. Check for voltage to the compressor clutch via pin T14/10. If voltage is present proceed with clutch and/or wiring diagnosis. If a pulsed voltage is present, look for a shorted compressor clutch.

    3. Check for good ground to pin T14/6.

    4. Check for 12 volts to pin T14/9 when the ignition is in the "on" position.

    5. Check for 12 volts to pin T14/4 via fuse #16 at all times. (Failure of this power supply can cause the cooling fans to run at high speed at all times).

    6. Check for 12 volts to pin T4a/1 and T4a/3 via fuses S164 and S180 respectively at all times.

    7. The fuses are located in the battery fuse box and have been a common failure point for the A/C system. Be sure to inspect the fuse box for heat damage or poor/loose connections.

      NOTE: It is critical to remove the battery fuse box and inspect all fuses and connections (from both top and bottom) for damage.

    8. Check for approximately 35% duty cycle from the A/C high pressure sensor at pin T14/2 with the ignition on but the compressor not running (duty cycle will increase as the high side pressure increases.

      NOTE: this is a ground side duty circuit. If tested with the positive lead of the DVOM to pin T14/2 a reading of 70% duty will be indicated. This is a normal reading when testing in this manner.

      A duty cycle above 90% or below 20% will command the compressor off and would indicate a faulty pressure sensor with the compressor not running and the refrigerant levels normal.

    9. Disconnect the 14-pin connector and verify continuity between pin T14/14 and T14/5. This checks the ambient switch (open circuit below 32 degrees F).

    10. Disconnect the 14-pin connector. Using a fused 12-volt jumper, apply power to pin T14/10. Compressor clutch should engage. Reconnect the 14-pin connector.

    11. Check for voltage at pin T14/13. This voltage signal comes from the Instrument panel and will normally vary from approximately 5 to 11 volts. If the temperature gauge in the Instrument panel detects an overheat condition it will ground this pin to shut off the compressor and run the cooling fans at high speed.

    12. Check for 11-volt reference voltage at pin T14/3 (the Powertrain Control Module (PCM) will ground this reference to request compressor shutdown for a Wide Open Throttle (WOT) condition).

      It is important to note that any problems with any other circuits at the fan module will cause loss of this voltage signal.

    13. If all tests pass, the Fan Control Module (FCM) is faulty and must be replaced.

    After performing the diagnostic procedures, poor/burned connections were discovered at the Battery Fuse Box.

    Replacing the damaged Battery Fuse Box restored proper voltage to the Fan Control Module and restored both A/C Compressor and Cooling Fan Operation.

    This Tech Tip Fix was performed and documented by Jim Newkirk, WORLDPAC Assist European Team Leader.

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