AC Compressor problem

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From volvo-forums, compressor clutch does not engage when compressor is hot:

Volio09 Apr 27 2009, 10:16 PM
Hello All,
I'm new to this forum but now after 80k (rewarding) miles with my 04.5' S40 T5 I have a frustrating problem and need help. My A/C system seems to have a intermittent issue such that the compressor cuts off after a few minutes and will not come back on until I leave it or the car off for some time. This issue just started on these hotter days (Atlanta area). I've a bit handy so I checked the refrigerent to verify the level is normal. Also, I reset the pressure switch so to rule out bad connection. I have no "MIL" lights or anything either. Again this really only happens occationally and only on hot (>80*) days... Any ideas would be greatly appreciated. Thanks!

russel May 13 2009, 08:51 AM
I'm experiencing the exact same problem with the same model volvo s40 T5 miles~90K. I found another guy with the same model and he is having the problem too. and
Anyway just took my car into to the shop and of course they want to just replace the compressor and everything involved; which is very expensive ($1200+).
Does anyone have a remedy for this?
They found my A/C coolant is low, but they said it wasn't low enough to induce the compressor to over heat and disengage. They also found a very small leak since the coolant is not too low and I have never recharged it since I bought the car in 04. Also I haven't checked to see if the condenser is full of debris. I found in other cars this was the root of most of my a/c problems. I'm going to pick the car up and check that because these volvo tech seem to be good at replacing parts and not so great at fixing problems.
However I do know that it could be the compressor is just bad but they checked for shorts etc and found no problems so this tells me the disengaging compressor/ over heating compressor rests with something other than the compressor itself.
Please help or post if you have the same a/c problem with you volvo s40.

russel May 14 2009, 07:25 AM
I went in to the shop and talked with the head tech there. He seem very knowledgeable and said that he has seen tons of s40's where the magnetic clutch on the a/c compressor can no longer engage when hot.
My understanding is that the clutch abrades over time and always returns to the original position unlike brake calipers that adjust position as the brake wears out. Since the clutch plate returns to the original position the magnet is no longer strong enough to engage the clutch for such a distance. The onset of this occurs when the compressor is very hot, because the magnetic field from the magnet is lower when heated.
I found where people refer to a "starter kit" ($20) for home a/c compressors to combat this problem. The "starter kit" is a relay with a capacitor which under normal operation siphons off a bit of power to store in the capacitor then the next time the a/c kicks in the capacitor drains quickly and increases the current to the electromagnet increasing the magnetic field and engaging the clutch plate.
I'm unable to find such a relay for a car, but the capacitor trick should work to increase the life of the compressor.
However, I was told the clutch life is design to fail just before the compressor, so under certain circumstances this cap/relay fix is just a band-aid that might last for an unknown amount of time (unless you really get into the permeation of the magnetic field)
If anybody has seen one of these cap/relays that will work with a S40 can you please post it.

volio09 Jun 14 2009, 03:57 PM
Thanks everyone for your ideas. I've been traveling, but finaly had time to check things and it seems Russel's mechanic is correct. It seems the clutch is not able to lock when hot. To test the theory, I disconnected the black wire (on compressor) from the socket then wedged a piece of aluminum foil inside. Then after pushing the wire back in, I had a little test point sticking out the side. I then waited for a hot day (+85*) and drove around until the problem occured. Then with the car running, I crawled under checked for voltage with my Fluke VOM and sure enough there was voltage there!

volio09 Jul 28 2009, 11:15 PM

Hi guys. I'm happy to report that I've managed to fix this AC problem by removing 2 of the 3 shim washers between clutch and clutch outer plate. I seen someone else do this on another web site on a older Volvo, but it's the same idea. See the link below. I removed the tire and inner fender plastic to see what I'm doing, but once that is done the hardest part is finding (or making) a puller tool. One thing I will suggest is measuring the clutch gap with a spark plug type gapper ("L" shaped) so you can get into the center of the clutch. You can't get an accurate measurement with a standard feeler gauge, as it will have to bend through the edge (not good). Anyway, as for me I needed to remove 2 of the 3 shims. Now, about a month later it's still working great here in +90 degree sun and traffic of ATL area.
Thanks for everyone's help and I hope many others with this problem read this too. The dealer is just taking your cash unnecessarily. Why replace the entire ac compressor (or even the clutch) if it's not needed (especially for cars with less than 100k miles).

local copy of the .pdf