A/C compressor troubleshooting quick help

Hi All,

My 2004 MK4 wagon's A/C started blowing warm last week. Using other posts I have found that my large fan had quit working, and replaced it. Both now run on low with the key in the ignition and A/C button pressed.

I also found that the compressor's clutch is not engaging. Yesterday, I turned on the car, had the A/C turned on at maximum and measured the voltage getting to it (I unplugged it and measured at the car side plug- in case that matters).The voltage appeared to vary, it would hang out around 7 volts for a few seconds then spike to 10 volts, and come back to 7, etc, etc, etc. Is that normal? Shouldn't it just be 12 volts?

I didn't know enough yesterday to check the resistance of the clutch coil, I hope to do that tonight, and also apply 12 v directly to it and see if I can engage it.

Any other help would be appreciated.

Check the resistance, its probably open (broken).

steve6 said:

Check the resistance, its probably open (broken).

Click to expand...

That is what I am hoping it is, since it looks like an easy and cheap enough fix. I would hate to have to replace the compressor.

The clutch coil is bad. The FCM does not apply full voltage to it, it only needs a "spike" to get it to engage, then less to hold it there. Current ramping.

Make sure the compressor is not locked up or the clutch is smoked, though, as many times that cooks the coil, and the root problem is elsewhere. In many cases, the compressor got overworked because of a non-operating cooling fan.

Pet peeve: A/C systems (in a car) cannot "blow hot air". They can cool the air, or not cool the air. Just something those of us in the industry chuckle about, because there can be a very distinct issue that could be a blend door stuck on warm, in which case you will get warm air, no matter what the A/C system is able to do.

Thank you oilhammer, you are right but I wrote that in the office, in a sweaty workshirt after a Florida spring morning drive...that was warm air

And BTW, I am able to turn the compressor by hand. I confirmed no resistance on the coil and no response to applied 12V. I ordered a replacement.

My kid's AC just quit and I suspect the coil as well; just waiting for it to cool off enough to not smoke my legs when I take the belly pan off.

So, I ordered the coil, $27 from amazon (could not find it anywhere else but ebay)... replaced it yesterday and now I have A/C!!!!!


The clutch holding wrench they rent at the auto-parts didn't work. I was able to use the impact wrench and it took care of the nut without needing to hold it.

Can you link to what you bought? I think I need one as well

steve6 said:

Can you link to what you bought? I think I need one as well

Click to expand...

https://smile.amazon.com/gp/product/B071GQ7FLL/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1


I see now that it is no longer available, when I bought it they had 5 of them. IIRC there were a few on ebay as well, but amazon prime had it to my door in two days.

Thanks

This is definately 1 part of my problem. My clutch coil has an open circuit also. I shall also look for a clutch coil on line and if anyone has a link to the replacement procedure for this I would appreciate it.. Again, thanks all.. much appreciated. Found a very helpful thread that I will use to consider my next moves.. Here is the link: http://forums.tdiclub.com/showthread.php?t=318248

ger164 said:

This is definately 1 part of my problem. My clutch coil has an open circuit also. I shall also look for a clutch coil on line and if anyone has a link to the replacement procedure for this I would appreciate it.. Again, thanks all.. much appreciated. Found a very helpful thread that I will use to consider my next moves.. Here is the link: http://forums.tdiclub.com/showthread.php?t=318248

Click to expand...

Check this video, it helped me visualize what I needed to do before actually doing it.
https://youtu.be/x7PHH5a8JK8

Very helpful FloridaMutt.. thanks kindly.. Time to muster up some Youtube university courage... cheers..

Completed the coil replacement today after receiving the coil from ebay. https://www.ebay.com/itm/A-C-AC-Com...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649
The part fit perfect and all the offered help made the job quite enjoyable..The clutch is now engaging....
I needed to use a two arm gear puller to get to the coil as it was on quite tight... Thanks everyone for your guidance...

oilhammer said:

Pet peeve: A/C systems (in a car) cannot "blow hot air". They can cool the air, or not cool the air. Just something those of us in the industry chuckle about, because there can be a very distinct issue that could be a blend door stuck on warm, in which case you will get warm air, no matter what the A/C system is able to do.

Click to expand...

What temperature air blows through the condenser?
Testicly, couldn't the system (car or home) be used for heat?

oilhammer said:

Pet peeve: A/C systems (in a car) cannot "blow hot air". They can cool the air, or not cool the air. Just something those of us in the industry chuckle about, because there can be a very distinct issue that could be a blend door stuck on warm, in which case you will get warm air, no matter what the A/C system is able to do.

Click to expand...

That depends on what is part of the "system". If it includes the air handler, you know the heater core is in there

when do your fans come on?

NurseGuy1987 said:

when do your fans come on?

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With the key in the ignition turned to on, and the a/c button turned on, they should both run.

DanG144'sa thread (sticky) covers the AC pretty complete and was written with your car as a basis.