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Old January 15th, 2010, 17:43   #1
blueskies
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Default A/C Compressor won't disengage electric clutch

Recently I started noticing my car was hard to start in the mornings and i thought it was a result of the cold weather we've been having. I would put my car on a trickle charger overnight and the ALH would start right up the next day.
Then I noticed that my AC push-button light would stay lit at times even when I had the blower set to the off position and the AC button not pressed in.
So I did an experiment:
I disconnected my battery overnight and hooked it up in the morning.
The car would start right up in the morning without assistance from a trickle charger or anything.
I noticed a "click" whenever I disconnected my battery.

Then, when I ruled out that it wasn't my battery. I watched my car as it was running. I found that although the A/C was off (vents sent to cabin/foot position, not defrost), the electric clutch on the A/C was staying engaged and dragging the engine. The only way I could make the A/C compressor disengage was by disconnecting the electrical connector on the A/C compressor.

Is anyone familiar enough with this system to help me figure out if a relay got stuck in the on position or whether something else went bad, thereby causing the A/C clutch to stay engaged even when the car wasn't running?

I don't know much about this, but do know that the A/C was the cause of my battery drain issue. Now that the electrical connector to the A/C compressor is disconnected, I have no issues.
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Old January 15th, 2010, 18:03   #2
gforce1108
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There's a real good troubleshooting procedure around here somewhere - I downloaded it, but don't remember where it was located. Most of it is related to the AC clutch not coming on, but the tests should still be relevant.
it's called A4_air_conditioning_troubleshooting_rev_4.pdf

I would guess it's a problem with the fan control module.
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Old January 15th, 2010, 18:07   #3
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You may have fan control module bad. It is located under battery. Also you may have melt that A/C switch at A/C control unit and it is giving power to compressor all time.You probably will need wiring diagram to check rest of stuff.
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Old January 16th, 2010, 07:08   #4
blueskies
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anyone have a wiring diagram for the A/C clutch circuit?

jetta 97, how do i troubleshoot a bad fan control module?
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Old January 16th, 2010, 07:20   #5
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What year and model is your car?
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Old January 16th, 2010, 16:05   #6
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99.5 jetta tdi, manual trans.
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Old January 16th, 2010, 20:58   #7
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Sorry for waiting. I was out all day.
Ok ,you need disconnect fan control module and see is A/C clutch will stop clicking while you disconnecting A/C plug(one you have disconnect now).
If is not clicking that is good and you have problem from A/C unit to fan control module.
Next pull out fuse 25 and see is it clutch still doing same thing.
Do you still have A/C button lighting up all time? Let me know what happened after these 2 steps then I will tell you next.
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Old January 16th, 2010, 21:03   #8
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