I have a 1995 850 turbo, and the A/C has perplexed me for two years now. First, the dreaded evaporator had to be replaced, so I did it----along with the receiver/dryer/accumulator and the HEPA environmental filter upgrade kit. (Don't want to do THAT again.) Afterwards, the A/C seemed to work fine for the rest of that season. The next season, my current issue began: At initial A/C start-up, the system works fine, holding at 40-60 degrees F. After 5-10 minutes (it varies) the temperature begins to climb above 60 and will continue upward (depending on the weather); sometimes it will cycle back on, sometimes it won't. I've checked and re-checked the charge, and it is fine. From what I can gather (and from what I've been told), it could be the pressostat or the ECC control unit, with the pressostat obviously being the cheaper of the two. Problem is, even the pressostat is considered an electrical part, so if you buy it, you've bought it----no returns. Therefore, I want to get the diagnosis right the first time. I was told that I could "jumper" the pressostat to test it, but I'm not quite clear on the procedure. Also, I've been told that in addition to the two above mentioned possibilites, it could also be the clutch or some other electrical signal fault. Any thoughts out there? HELP!!!

Thanks,
Wes
Virginia

Wes, your story sounds just like mine with my 1994 NA 850 with 155kmiles.
What appears to be happening is that the thermal switch on your a/c compressor is telling the clutch to disengage when a certain temperature on the compressor is reached. The most common cause for this condition is that due to wear, the gap between the coil side on your compressor clutch and the front plate has increased beyond specs. Some will tell you to jump the temperature sensor on the compressor, which is an easy but temporary fix. Don't do it.
The correct fix is to remove the the compressor pulley, and remove two of the spacer washers located behind it. Before you do anything, with car off check the gap between the pulley and the clucth plate with a feeler gauge. If it is above .7mm you found your problem. Why does the thermal switch go off? Because heat weakens the electric field on the clutch, it starts to slip just enough to generate more heat in the compressor, and off the switch goes.

Good Luck?
Luis

Do you have to remove the compressor from its bracket to remove the clutch spacers?

what is the size of the bolt to unscrew?

I checked and the pulley seems to be very near the chassis. If I have to remove it, can I let it connected to its freon lines? (i dont want to have to recharge it if it is possible)

thanks a lot

Jean-Philippe

You do need to disconnect the compressor from the engine to remove the clutch. You will also need to get a pully/clutch removal tool. Auto Zone has one you can borrow. Someone posted a procedure on how to do the job by disconnecting the compressor but leaving the lines connected. I think it would be best to completly remove the compressor. Once you go to all the trouble to disconnect the compressor you don't have to do much more to remove it and recharge. It makes it much easier to work on. I bought a compressor on Ebay last year so I have one with a worn clutch.
Here it is. I think it was originally posted on Volvospeed. Good Luck.

Volvo 850 AC Compressor Clutch Removal
1. Don't discharge the A/C system.
2. Remove the bolt holding the receiver dryer bracket to the car, but don't
disconnect the receiver/dryer.
3. The manual tells you to remove the 2 radiator bolts and swing the radiator
forward. This looks like a bad idea to me. If you do that, nothing is holding in the
radiator but the hoses. I removed the right hand bolt and loosened the left hand
bolt, so that the right side could swing forward.
4. Unbolt the compressor and move it to where you can access the center bolt on
the clutch plate. Remove the bolt. You probably need an air impact wrench to get
it off, unless you can stop the plate from turning when you try to unbolt the bolt.
(Don't over torque it going back in. The spec is 10 ft/lbs.)
5. The manual tells you to pull off the clutch plate. It will not come off. What they
don't tell you is that there are 3 5MM holes in the plate. You need to get three
5MM bolts, about 1 1/2" long, and thread them into the holes. Tighten them
evenly, and it will pull the plate off. If you don't do it evenly, the plate will get
cocked and stop coming off.
6. Using a six inch wide, 2 jaw puller, remove the pulley. You have to rig
something up to protect the end of the compressor shaft. If you damage this shaft,
you will be buying a new compressor.
7. Using an impact screwdriver, remove the 3 screws holding the clutch coil to the
compressor.
8. When reassembling, don't forget to put in the clutch plate spacer shim(s). The
new clutch comes with 3. I used the one shim that was in the old clutch. (It was
stuck inside the clutch plate, so you have to go look for it.)
Re-assembly is the reverse of dis-assembly.
--
Tom 69-1800S, 72-1800ES, 96-850T

This is the best explanation I've heard...mine is doing something similar now but still blowing cold air and I don't think I'm losing and of the cooling gas. I'll have the gap measure and go from there.
--
1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon

To make the jump, just get a short piece of wire and connect both sides of the pressostat switch - the compressor clutch should engage. Remember, this switch only gets tripped when the pressure gets too low, turning the clutch off and when the pressure gets up to 45psi it will re-engage the clutch.

It sounds like the 60F degrees problem might be the radiator fan not kicking in. Check it out.

Klaus
--
98 V70Rawd(101Kmi), 95 854T(85K mi), 75 164E(173K mi)