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.
Diagnostic Procedures:
- 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. - 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.
- Check for good ground to pin T14/6.
- Check for 12 volts to pin T14/9 when the ignition is in the "on" position.
- 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).
- Check for 12 volts to pin T4a/1 and T4a/3 via fuses S164 and S180 respectively at all times.
- 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. - 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).
- 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.
- 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.
- 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. - If all tests pass, the Fan Control Module (FCM) is faulty and must be replaced.
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.
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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