A/C only works with Fan at Max setting

CAJUNVOLVO

MEMBER
VOLVO 850

94 volvo 850, non-turbo, auto, manual climate control, 250,000 miles.

A/C delivers cold air, freon level/pressure good, but A/C clutch dis-engages after about 5-10 minutes when using low or medium fan settings. With fan/blower on max position A/C works continuously. No problem.

When A/C stops, I have to wait 3-5 minutes with A/C and/or fan turned off, then clutch will re-engage.

Most prevalent on hot days when air temp is 80 F or above.

Again, not a cycling problem due to low freon. With blower at max speed (#4) A/C will work continuously, but at any other fan speed, A/C works for a while, then cuts out.

This is used car, previous owner said he thought there might be leak in system. Had system checked, no leak with any components under the hood, but suspect maybe small, small leak in evaporator as I have to add can of freon every 60-90 days.

Appreciate your help.

Thanks

Chuck

3 Replies

DPWD23

MECHANIC
136 POSTS

You stated that the problem happens more on humid days. That's understandable.
On the evaporator (inside car) their is likely a little temperature probe. My guess is that it is touching the core, or is positioned incorrectly (may have gotten bumped when previous owner had a heater core replaced or something).
I would consult a repair manual for something regarding this sensor, as it will also use that to cycle the compressor off and on. It should also be a fairly cheap part, ask at the parts counter if they have one to show you, so you know what you are looking for.

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Saturday, August 4th, 2007 AT 1:08 AM

CAJUNVOLVO

MEMBER
4 POSTS

Thanks for trying to help, but nowhere in literature, diagrams, schematics for MANUAL a/c system have I noticed anything about temperature probe in/around evaporator.

Yes temp sensors for auto a/c, but not in my plain vanilla 850.

What have I missed?

Thanks

Chuck

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Monday, August 6th, 2007 AT 3:56 PM

CAJUNVOLVO

MEMBER
4 POSTS

Have cured problem, thanks to recent info in Volvospeed 850 forum provided by "Rower".

Not mentioned in detail on this forum, but before posting my question, I had checked A/C system "stem-to-stern" using schematics, trouble-shooting flow charts found on the Web or by subscription. Everything in my system checked OK as far as voltages and pressures etc.

But why only reliable operation at max fan setting?

Did numerous pressure and voltage tests. Nothing out of spec.

Then read comments by Rower and others in various forums. My final check.

Ran system until it quit. Checked voltage going to compressor/clutch. Showed 12v. So that indicated (to me) that all other components (sensors, relays etc) were functioning properly. As I had ascertained by multiple tests.

Then did Rower's thing. Using stick of wood, pushed against clutch plate. And woopy, A/C engaged again.

So either go to shop for mega buck repair/replacement, or give his cure a chance.

Looking at exposed clutch plate there are three places where it rides on other portions of clutch assembly. By adding ( and gluing) three small pieces of plastic about thickness of a credit card under those points gap for old clutch is reduced.

I drove 150 miles today in 95+ degree heat. A/C worked fine on all fan settings.

Total cost: 15 minutes work, $3.00 for super glue, and two beers.

Hope this helps someone.

Chuck

PS: I have pics from Rower, but not mine to release.

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Tuesday, August 7th, 2007 AT 5:22 PM