The ac on my sons volvo was not coming on, so I assumed it might be low on refrigerant. However, when I jumper the wires to engage the compressor it would not come on. I never had this problem before. A couple of weeks later I tried the same thing and the compressor kicked, in a added some refrig. and the system worked fine. Came on by itself and ran like it should. The next time he went to use it, it would not work. Again I tried the jump the wires and the compressor would not come on. I know the compressor works and that the system is charged, so what could cause this strange behavior. Also, does anyone know why the fan blower will not turn off unless you take the number 5 fuse out. This is a climate controlled car.

1) You have a post-1996 850 (ie, OBD plugs in rt. above shift lever)?
2) You've gotten NO fault code from a/c (ie, the "a/c On" and the "Rec" lights flash for 20 sec)?
The good news is that it sounds electrical to me.

You removed probably the a/c relay behind the glovebox. My best educated guess (emphasize GUESS) is that there's a problem w/ the E. Climate Control POWER STAGE -- aka, "ECC Output (Power) Stage." This is located beside a/c relay, behind glovebox.

A faulty actual fan SWITCH/rheastat would, I think?, trigger a fault code, but the Power Stage to my knowledge doesn't necessarily do so.
What I definitely do NOT know is whether a screwy Power Stage would 100% affect compressor's function. I suspect it would.
3) (Have you tried to apply power directly to compressor?)
4) I guess you've tried all possible combinations to try to get fan off. Have you tried these . . . This is grabbin' at straws:
*tried fan switch on AUTO and through entire range of MANUAL? Try both of those with these combos:
*tried fan switch with a/c OFF and temps turned all the way to Hot
* " " " " " " " " " " " and defrost ON

I will look in there again when the car is home. My son emailed me today and said the ac worked fine yesterday on a long trip, then when he went out again it would not work. Is the power stage difficult to remove, and about what should I expect to pay for one. I need to try something soon, it is driving me crazy. I have had a bunch of Volvo's and I have never seen cars with so many AC problems, I swear everyone I have owned has had AC issues, never had problems with any other brand car.

There is absolutely nothing in this world more sicknin' than an intermittent car problem!

I guess that your son has to reinsert the #5 fuse to run the a/c? Still on MAX fan speed? One correction ... I asked if you had applied battery voltage directly to the compressor but just re-read your post about "jumping the compressor." Sounds like you already put 12V directly on compressor? If so, that's a big oversight on my part b/c it would be big-time important if that's what you did. (I assumed at the time that you jumpered the low-pressure switch.)

Power Stage is very simple to remove after taking out glovebox. BUT,although electrical problems are often VERY intermittent like this, I'm not confident enough to say buy the part.

Ideas other than what I posted before:
1) A/C Relay: I know you pulled it for the non-stop blower fan, but you can always have 2 unrelated problems causing your 2 symptoms of perma-fan AND a/c. From Volvo/Mitchell ...

"A/C Relay Check: Remove relay. Connect battery positive lead to relay terminal No. 1 and neg. lead to relay term. 3. Continuity should be present b/t relay terminals 2 and 4. If cont. not present, replace relay."

Many order replacement parts from IPD and the like (typically w/ good results), but don't assume that genuine Volvo parts are more
expensive. I order almost 100% of the time from Houston Volvo--Miguel has helped me in the past. They offer a big, big discount over what the local Volvo Service/Parts would charge! 1-800-468-0041
I had a few other questions to ask them today, so I asked them about your problem. They said that they sell a fair # of the Power Stages and that it sounds "consistent" with your perma-fan problem but that all electrical parts are non-refundable . . . get 2nd opinion . . . etc, etc. Hope it helps. (You know anyone else w/ same car to swap out known good one?)

The price for 1997 (I guessed) 850 was $102, but 1997 cars used two different power stages depending on VIN number.

You have been a great help, the next time I see the car I will try some of your suggestions. You are the second person that suggest a powerstage. I know what you mean about intermittant problem, very difficult to solve, however the permfan is consistant. He does remove the fuse everytime he want to use it and it is always on high.

1) "climate controlled car" -- I guess you mean that it has the Electronic Climate Control (with the temperature dial w/ numbered degrees)?
If so, are you getting any a/c fault codes?
Does that a/c fan stay on 100%, even when the whole a/c system is set to off (ie, not on automatic)?
2) Do you remember what the low-pressure reading was? Ballpark?

Here's Volvo lit for the Elect.ClimateControl (ECC):

"The a/c relay (is) activated by both the ECC module and the Eng.Control Module (ECM). The ECM turns a/c comp. off when engine is at full accel, at high eng. temp, and for 5-10 seconds after starting engine."

3) Is your engine temp. OK on the instrument panel gauge?
4) Is your Radiator Fan coming on within seconds of turning the a/c on? If not, it's still not conclusive b/c the same problem (non-Radiator Fan problem) could be causing the a/c AND the R. fan to not work. Does the R. Fan come on when engine temp gets high (after summer idling / driving in city for a while)? You may have to test the R.Fan and its relay if you aren't sure.

I will attempt to answer your questions with what I know.
Yes it is an ECC system
guage reads 27lbs
Put a OBDII on it and no codes showed up.
I heard the cooling fan running when the car was idling, Engine temp seemed fine. The heater/ac fan has been running constantly on high now for several months, started in early winter. He has to take out the number 5 30amp fuse to get it to go off.
Hope this helps.

I'll try to help out Sunday pm (on the way out now, but didn't want you to think I forgot)

Thanks.

You do not say how many miles on the clock. If it is high, say 100k, your compressor clutch may be worn so that the coil will not pull it in. First, when it fails to come in when you think it should, very carefully give the end of the clutch a tap with a long stick. If it clicks in, that could be your problem. With a bit of ingenuity it can be adjusted. See the following link to the end:
http://www.volvoclub.org.uk/dc/dcboard.php?az=show_topic&forum=14&topic_id=19712&mesg_id=19712&page=8
--
Graham

I replaced the compressor last summer with one that came off of a car with 24,000 miles, doesn't mean that your suggestion could not be the problem. When he brings the car home again I will try that. Thanks

a few questions:
Am I correct in assumming that the "fan blower" you speak of is the climate / dash fan (ie, not the radiator cooling fan)?
Have you hooked up a gauge to the low-side a/c line (w/ compressor engaged if possible)?
"Ran like it should" means cold ... really cold? (happen to know the temp at duct output)?

Yes you are correct, it is the dash fan. I even pulled the glovebox and removed the only relay that was visible and the fan continued to run. I put a gauge on the low pressure side and the system has a full charge and blows around 42 degrees, the compressor just will not come on even when jumped. The only time it worked was the time I added the refrigerant and put the gauge on it. Then it worked two more times that day and has not worked since, again even when trying to jump it.