Quick questions:
1) Has anyone here owned an 850 with the "intermittent a/c" problem who isolated the cause 100% as the Compressor Overheat/Thermal Switch? (the switch that screws directly into the compressor)
2) Is there a way to quickly test / rule out this switch?

If the a/c goes out after working 10 minutes and the driver shuts down the car entirely (presumably resetting the computer / relays, etc?) and then restarts after a minute, would the a/c work again? (ie, is that a/c loop reset after restarting the engine?)

Thanks!

Well, my wife is considering getting rid of this car just because of this problem so I hope we all find an answer! I had the evap replaced 2 summers ago at a cost of well over $1k and she still doesn't think it works well. After the first real hot day in north florida today, she described the exact symptoms being discussed. Couple of quick questions...

1. Any risk bypassing the overheat switch?
2. What does it look like (overheat switch, I tried looking for it and see what appears to be a fuse, a detailed description would be greatly appreciated!

We set a record on dash lights (5!), so I'm finally fixing everything.

Here's the list:
1. Replacing alternator (battery dying, only 13V at battery while running with minimized load.

2. ABS control module. Pulled it off tonight, will be sending out for repair

3. Loosing coolant. Had visible buildup at first connector behind resevoir, clean, trimmed hose, waiting to see if loss continues.

4. Check engine light. Codes a plenty! ( 0172 , and cylinder misfire codes ) Will be inspecting vacuum lines, cleaned MAF, ordered tune up supplies and will install next week. Reset codes and hope for the best!

5. Will check AC clutch gap and adjust if out of tolerance.

6. Mushy brakes, need to bleed, any recommendations? (new rotors/pads <6 months)

7. Any other suggestions?

Thanks in advance!

NvrLose,

You'll probably get a better response to your post if you start a new thread since lots of it isn't related to the intermittent A/C problem.

My coolant was also low and we recently refilled the reservoir...will need to watch the level too.

I had my alternator rebuilt at an indy auto electric shop. They were considerably less $$ than the dealer.
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'95 854T 125,000

Thanks Cley & Icelandic! Your advice is EXACTLY what I wanted and had not been able to locate: some specific steps to isolate the cause of this mystery!

I'm not sure if I'll have time to solve my mystery before I go out of town tomorrow am, so I may have to re-post next Monday (it will be conveniently hotter in Knoxville then anyway!).

I promise I'll let you all know the results (any other advice in the meantime welcome).

When I was wrestling with this two years ago, I was told by a Volvo mechanic that you could unplug the overheat switch (on the back of the compressor and simply eliminate it by plugging in the wiring harness connectors so that the switch was eliminated. I do not know if this is true, because my car (a '99 V70) does not use an overheat switch. They got smart and eliminated it in 1999.

In my case, I replaced the compressor clutch, and the problem went away until yesterday. I am really grateful for Cley's advice about the compressor clutch gap. I'll bet that is the problem. The clutch gap is not documented anywhere, so I just re-used my original shims when I did the replacement.

I had the same problem and after a lot of investigation, i read someplace that I should check the gap between the coil and the clutch plate on the compressor.
In my car it was at 1mm. Correct gap should be half that much. What happens is this: With the wear of the clutch and with the widening of the gap, the magnetic field generated by the coil will allow for some slipping of the clutch, which generates heat. Heat on the clutch is transmitted to the coil. A hotter coil generates a weaker field and the clutch disengages, simply because the magnetic field is unable to pull the clutch plate, unless it cools off.

The correction is relativelly simple. What I did was to remove the serpentine belt, take out the screws holding the compressor in place ( without taking out the gas pipes and without degasing the system) moved the compressor a little so that I could remove the clutch plate and them removed a couple of the spacer washers behind it ( there are three) and reasembled) gap came down to .4mm . Worked perfectly. If you want to check if that is your problem, drive thge car with ac on until it stops cooling. Stop the car, leave engine and ac on, open the hood and very carefully tap the center of the compressor clutch plate with a heavy screw driver. If it engages, you found the problem.

Good Luck
Icelandic

There's a really good explanation of the 850 system at "au.geocities.com/ozbrick850/aircon-keithP.html". Hot humid conditions can cause the compressor heat sensor to activate.

Thanks for the link. I studied that info last weekend, and it is a great resource. His advice (as well as several Brickboarders') on the Compressor Overheat Switch brought it to my attention as a possibility.

It's just that over the years I've learned the hard way how important it is to try to get a grasp of just HOW likely a particular possibility really is before spending time --and scraped knuckles-- on it.

That's why I'm looking for someone, anyone, who has actually fixed their "intermittent A/C problem" with replacing or temporarily bypassing this compressor switch. Despite all the great advice (seriously), no one seems to fall into this category. No disrespect intended and thanks for all help!

I hope you get someone who has the real scoop on this.

I turn mine A/C switch off at long red lights or if I have to idle. So far that is working to keep it cold while driving...but doesn't help during the long light in 90 degree sunshine...like today. Actually, it wasn't so bad...I kept the fan running and it didn't start to blow warm until the light was a about to change. Then got cold within a 100 feet or two once I turned it on.

I don't know what overheat switch you are speaking of...unless it is the low pressure switch.

Here are some answers a Volvo tech recently gave me on another board forum, (don't know if they will be helpful to you at all):

There is 2 things that can be happening.One the low pressure switch is bad and the A/C is freezing up.Or the A/C compressor is going bad.When they get hot the clutch will disengage and still have power to it.It works when the compressor is cool but once it warms up it stops.A good way to tell it let it sit on for a little.Or drive it real easy for a while.Then when you can step on it really hard hold it and let it shift at the max RPM for the gears from a stop.Atleast first and second.Then if it starts blowing warm it is the compressor.

Another answer:

If it happens again have him open the hood and look at the pipes going into the firewall on the passenger side.If they have ice on them then the low pressure switch is bad.If that isn't it have him look at the Compressor it is all the way at the bottom towards the front of the car.If the center is not spinning then most likely it is bad.Most of the time if you turn it off fro like 10 min then it will work again for a little while.

Another answer:

It is still possible that both is the cause.But if it is not icing then the compressor is bad.The compressor is bad just from age nothing you did.It is really the clutch itself that is bad.Most of the time it is just better to replace the compressor than just the clutch.Most of the time if you just replace the clutch the compressor goes shortly after that.
Another thing he can do to help is when it stops keep a metal hanger or something like that in the car.It needs to be able to stick to a magnet.If that happens with the compressor see if it sticks to the compress clutch the center part of the pulley.That would mean the compressor is still magnatized and the clutch is disengadged.Then it is bad.
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I was told last week that my compressor is good but the clutch is the problem.
He thought the switches were working fine. I think I would prefer that it just be a low pressure switch. My husband it sick of dumping $$$ into this car.
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'95 854T 125,000

This link may help regarding the method of adjusting the clutch:

http://www.volvoclub.org.uk/dc/dcboard.php?az=show_topic&forum=14&topic_id=19712&mesg_id=19712&page=2