Volvo 850 AC Compressor wont Activate

alexk243 · Post by **alexk243** » 16 Mar 2012, 11:40

So i finally decided that I need Air Conditioning in my Volvo 850. Added some leak sealer/oil/leak detector to it. Got it up to about 25psi (may have been at 0 prior to this) and the AC clutch would not engage on the compressor. Do I just need to add more refrigerant or is there something I should do because it was at zero?

Pressure dropped after the car was off but held at 10psi for a bit.

Post by **fazool** » 16 Mar 2012, 11:55

There is a common issue with many of the A/C compressors.

The clutch is electro-magnetic and normally its in the released free-wheeling state. The belt just spins the pulley. When the A/C switches on, the electric coil gets powered and creates a magnetic force which pulls the pulley inward toward the compressor. When this happens it connects with the compressor and spins it.

Its like a clutch on your transmission - they use really big powerful springs to force the pressure plate and the clutch plate together. This A/C clutch needs a big force too but it comes from the electro-magnet.

In order for this to work, the gap has to be very very small and precisely controlled. Magnetic force is a fourth order function of distance (R^4) so its a huge exponential effect of distance. If the gap is a little oversized, the magnetic pull drops WAY off.

As the clutch wears down from normal usage, this gap increases until its too far and the electro-magnet cannot PULL the clutch in.

I forget the exact numbers but I think the gap has to be between .0035-.0075" (don't quote me on that I forget the exact number but its something like that).

When the clutch wears down, you can disassemble it and remove internal spacer shims until the gap is correct again.

As a quickie band-aid fix, look up something called the "bread clip fix" which is a way of shimming the clutch fomr the outside.

One way to sort of see if this is your condition is to run the engine and turn the A/C on. Then CAREFULLY (very carefully) using a wooden brrom handle push or tap your A/C clutch to see if a little nudge will give it enough to get grabbed by the magnet.

Post by **rmmagow** » 16 Mar 2012, 13:36

It doesn't sound like you did an evacuate and proper recharge. This is something best left to the pros. Having non-compressible air in the system is not a good thing. You really need to evacuate and recharge correctly. Be careful. if you're using the little cans, they can blow up and ruin your haircut.

falconbrother · Post by **falconbrother** » 16 Mar 2012, 16:12

You can get a vacuum pump at Harbor Freight for cheap. You'll need a manifold gauge set too. Then you can pull the air and moisture out. Might be cheaper to have a shop do it. They can determine the extent of your leak, if you have one. Get the R134 while it's cheap. It's fixing to get expensive I'm afraid. My buddy works for a company that's designing the new systems for cars and R134 is going the way of the dodo bird.

alexk243 · Post by **alexk243** » 18 Mar 2012, 13:51

I agree that the compressor may have some issues, but I was more worried about fixing the leak first. then looking at the compressor. if I am at 0psi now there is no doubt I have a leak and as I cant seem to locate the red dye that was added it sounds like I would have to pull off the dash. What would a shop charge to fix ac?

Also what would cause the cans to explode?

Post by **jblackburn** » 18 Mar 2012, 18:36

Sounds like you've got the famous Volvo evaporator leak.

Join the club - mine doesn't work right now either.

You can see how long it will hold a charge once having the proper evacuation done, but it will probably only be for a few weeks before you'll have to keep adding cans of R-134.

An evaporator job is about $1200+ as the whole dash has to be removed, or one day of pure hell doing the whole thing yourself.

Post by **Fish stick88** » 18 Mar 2012, 19:22

Justin, I was quoted 2200 by the dealership.
Where do you go!?
Think about it this way! Assuming at 12 hr fix, Its like they're paying you $100 An hour!!! Of course, your marginal cost of whatever else you could be doing that day!

PLUS. You get the experience, and pride of working on one of the most PITA jobs on Volvos!

I'm doing it next weekend, maybe i'll change my thoughts...
AJ

alexk243 · Post by **alexk243** » 19 Mar 2012, 11:27

If I did it myself what would be the cost of parts? (what parts do I need?)

Post by **jblackburn** » 19 Mar 2012, 13:50

Everything you should need to know about it:

http://www.woodjoiner.com/volvo/VolvoEvapReplace.pdf

alexk243 · Post by **alexk243** » 20 Mar 2012, 10:19

That is a really useful guide. Amazing someone put this time in to make that for free.

How much is the evaporator core? and where can I get one?