OK, its hot here in the midwest and I've got an AC problem. The car is my 94 850 turbo wagon. The problem is that on a very hot day like today (100+ degrees) the AC will blow cold for a while on any given temp setting, then the cold air stops and warm air is blown in. I can turn down the temp control from 72 to 66, then the problem repeats itself, first cold, then warm air. I then turn the temp control back up to 72 and the cycle is repeated. This is all done with the air mix set to introduce a minimum of hot outside air and the climate control set to recirculate. When the ac is blowing cold, it is blowing very cold air, so I don't believe a charge is the problem. The car had the evaporator repaired previously. Any thoughts or advice would be greatly appreciated.

Thanks,
Bert

Thank you all for the input. I pulled the interior temp sensor covers to find both sensors covered with dust and hair. I cleaned them with a toothpick and a light shot of compressed air. Everything is working fine now.

Thanks,
Bert

Iy 1997 850 didi the same exact thing. Volvo Master Mechanic advised that it was extremely low on refridgerant. Re-cahrged now it works fine. Nothing too complicated. I was preplexed by the warm then cold thing, thought it could be a valve or something.

Kevin

Before you guys change anything try by passing hi temp switch at the back of the compressor. It should fix it for 94 & 95 850s. Give me your email address and I will send you a drawing. If it doesn't work just wire the sensor back, no harm done.

Aaron

Dear Aaron , could you email me the compressor temp switch bipass diagram at Paul.Bailey@tesco.net, thanks

Hi, I am still waiting on my password, so for now, I "claim to be..."

Anyway, I have a 95' 850 turbo. HAD the same problem. I changed the evaporator (myself, mind you, and yes I am quite proud---but I would NEVER want to do it again!)

I see that you have already had your evaporator changed. Now, there are a few questions: Who did it? If it was Volvo or a certified Volvo, they should have updated your car with the "pollen filter kit". Volvo later determined that this seemed to greatly contribute to the a/c problems with these models, primarily regarding the evaporator. I can go into it if you'd like, but for now, let's just figure out what YOUR problem might be. If you haven't had the filter update, I would HIGHLY suggest you get it, so you won't be right back in another evap. problem again. However, I doubt seriously that this is the problem now. Whoever did the work, find out if they changed the orifice/expansion valve when they did the evap. work. If they didn't, CHANGE IT! It is supposed to be changed along with any a/c work where you open the system, and can cause the problems you are having. (Its easy to do if you want to do it yourself--let me know and I'll tell you how.)

If it was changed, then let's move on...

Did they replace the receiver/dryer (also referred to as the accumulator)? If not, this also could be your problem. This component is critical to the proper function of your a/c, and it is supposed to be replaced whenever you open your system, like on an evap. job. In essence, when you replace the evaporator, you are also supposed to replace the receiver/dryer and the orifice/expansion valve, all together on the same job. Again, I can go into detail, but later, if you wish.

If they did all of this, then you need to start looking at other things, like your compressor. Run your a/c WIDE open, FULL BLAST, set on recirculate. Open your hood and watch your compressor. The clutch on the compressor should start opening and closing soon after you turn on the a/c. (Be patient, sometimes it can take a bit before it starts working.) The normal operation of the compressor should see the clutch working on and off, at intermittent intervals. If it sticks open or closed, then this could also be your problem. If this happens, it could also mean that you have a pressostat switch problem, or some other control problem that is causing the compressor to not function properly. WARNING: If your compressor IS doing this, you need to address the issue very soon, because the compressor sticking can eventually burn up your compressor, and/or cause other problems that you would normally not have.

Before you start worrying about your compressor or other control, CHECK YOUR FAULT CODES! Actually, this is the FIRST thing you should do. Your car is designed to help you keep it "healthy" by telling you when its "sick" and what's wrong with it--you just need to know how to talk to it. Now, any shop will gladly "talk" to it for you, because they have all the expensive software and equipment to do it. But, it will cost you. Your car should be (My car is, and its only one year newer than yours) equipped with a diagnostic module under the hood, next to the wiper washer fluid reservoir. If you don't know how to check it, let me know and I'll send you the info on how.

The reason you should get the codes first is because if its a pressostat, switch, electrical signal/control or other type problem, the car will know it and will store a code to tell you exactly whats wrong. If, however, you don't get any codes, then you can assume that all control/signal parts of the system are okay, so you will know to begin looking at a component.

One last note: It can be highly likely that, even IF they DID replace your orifice/expansion valve AND your receiver, you could still have a receiver issue. This is because of the EXTREME sensitivity of the receiver and the exacting care that must be taken whenever you replace one. If whoever replaced it left it "open" to the air (in other words, if they left either of the pipes unplugged) for more than 10 minutes, then your "new" receiver could have been ruined. This is because of the function of the receiver, which is to remove moisture from the refrigerant--which ALSO removes moisture from the air, get it??? Aaaannndd...the dissicant sack that is inside the receiver (the thing that holds the moisture) will reach maximum saturation (fill up) in about 10 minutes if left open. So, if this was the case, then basically they installed a "new" receiver with a "full bladder", when it should be dry as a bone. And...

even if they did take steps to keep it plugged until just before hooking all connections together and sealing the system, if they didn't pull a vacuum on the a/c system BEFORE charging it with refrigerant, well then, there's your problem as well.

Let me know if I can help further.

Not trying to shoot you down here but some of your info is incorrect. Volvo doesn't require the latest "evap kit" which only adds a few more parts but it's highly advised. The kit consists of the evap, pollen filter kit, accumulator (not receiver/dryer) and blower motor air restrictor tape. That kit also adds to the cost of the job and believe it or not, most customers decline to go that route when given a choice as it's more money. The job can effectively be done w/o all the extra parts but it's better to go the suggested route if one plans to keep the car for many years.
As far as the oriface tube is concerned (has no expansion valve), it's never replaced unless there's a specific reason, diagnosed by guages. Most cars never have those replaced as they very rarely fair.
As for the idea of the pollen filter totally curing evap problems as originally thought, not so. This summer we're seeing X70s with leaking evaps, doing one now as we speak btw. Those have the same evaps but they're just lasting a little longer than most did in 850s. I think the pollen filters help a bit, definately keep the evap and ducts cleaner but it's not the total solution either.

Unlike the other guys problem with MCC, your car probably has ECC (electronic climate control) and from your description I think that you have a sensor problem related to your ECC system.
If ECC, do the ECC LEDs flash indicating an electrical fault? Whether they do or not, one should check for any ECC codes first.
Another idea that comes to mind and being that you recently had your evap replaced is that it's possible that one of your defroster vent temp sensors fell out of it's correct location, a hole in the bottom side of each defroster vent (L&R). They're held in by plastic straps but I've seen where they'll fall out (even if slightly) and that will then cause the ECC system to malfunction going from cold to hot, sometimes hot on one side and cold on another yet not detectable by reading fault codes as it's electrically OK.
One can see the right side sensor by removing the glove box and looking to the upper left of it and the left side's harder to see as the knee bolster needs to be removed first.
If your evap job was recent, whoever did it might be inclined to look at it for free but that's a "might", depends on the individual.

Sounds like whoever did evap,did not draw down system long enough and there is still moisture circulating. When this moisture encounters the orifice, it can freeze and clog passageway temporarily and cause warm air. Try hooking up pressure gauges while running A/C and see if pressure spikes when air gets warm. "whilst.
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whilst