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AC Diagnosis?

My 95 Volvo 850T with 167K miles has an AC problem. Living in Phoenix where today it will be 105 and tomorrow 115.

In these very high temp days, the AC cycles. Blows cool air for a few minutes, cuts out to normal (hot) air, then back to cool for just a minute or so. If the outside temp were only 80 or so, the AC would probably work pretty good.

Took it to a reliable repair shop (CT Recommended) but early in the morning (when it was in the 70s.) They checked the refrigerant level, found it low, replaced it, added dye and off I drove. The next day, it again began to cycle.

They did recheck the system to see if the dye indicated any subsequent leaks and found none.

This car has ‘auto air’ and temp adjustments for both driver and passenger. The AC works (when it does work) ONLY if the temp adjustment is set to the lowest (blue) mark which is below 60 degrees. Anything higher and it blows warm/hot air.

The garage is willing to look at it again – and spend up to an hour at no further cost to see what they can find.

Any ideas on what to focus on?

– HOT in Phoenix

Did you take the car to a shop specializing in AC, or to a regular mechanic who also does AC work?

If the compressor is cycling correctly and the pressures within the system are in the normal range, someone is going to have to start trouble-shooting the automatic climate control system, which can be time-consuming.

It is normal for the air conditioning to cycle off and on, although it is not supposed to be noticeable. It will cycle off when you demand more power from the engine. If I am right about this car, its power to weight ratio probably causes the air conditioner to cycle off every time you accelerate. If the air conditioning system checks out fine, I would look to the engine for problems. I would start by checking the turbo.

Thanks mcparadise.

A general shop - very highly rated and one I’ve used before. The service writer indicated it could be the automatic climate control system – and that that part alone was $900 from Volvo. The vehicle may be worth $900 total.

The turbo was checked out about 3K miles ago and was OK. I’m not a lead-foot driver and don’t think the turbo kicks in much.

Once it reaches the stage where the AC turns ‘hot’, it may be 5-10 minutes before it blows cool again. I’ve tried turning off the AC switch for several minutes. Sometimes when I turn it back on again, I can feel the ‘drag’ of the compressor kicking in and cool air comes out for 2-3 minutes. Sometimes I can’t feel that ‘drag’ and only hot air comes out.

Anyone have input on why this gets worse as the ambient air temperature gets over 90 degrees?

A clue that every AC tech wants are the system pressures when the failure occurs.

I don’t have a Volvo, but the Automatic Climate Control trouble-shooting section of the repair manual for my car goes on for many, many pages. There are sensors that feed information to the ACC computer, and if one is faulty the climate control won’t work correctly.

This is when you need an AC specialist, someone who’s used to tracking down these strange problems.

Good luck. You really need functioning AC where you live.

mcparadise is right, you need to see an A/C specialist about this. Although your shop is highly rated, not all A/C technicians are created equal.

I sometimes get my car serviced at a tire chain store and I have been quite satisfied with the quality of their work. However, I found the A/C tech at one location was not as good as the A/C tech at another location, and only the better technician was able to find the problem with my A/C. It sounds like you will have to do the same and get a second opinion to find out what is wrong. Even the second store had a hard time identifying my problem, so I asked the technician to commute in my car for a few days until he could make the problem repeat itself. It took him a week, but he eventually figured it out and fixed the problem.

I’m so dumb … how do you “check the refrigerant level”.
As far as I know, the a/c system pressure will stay the same as long as there is liquid refrigerant in the system. So the only way to check the level is to drain the refrigerant and weigh it.
Is that what the shop did??

I believe that is what they did Gary. They said they put in 1.5 pounds of refrigerant and the dye.

The pressure is only constant after the compressor builds pressure in the system. After the system is turned off, the pressure drops.

They hooked up a gauge to the freon filling port after running the air conditioner for a few minutes. I believe that is how they checked the level of refrigerant in your system.