AC stops working when car gets hot


#1

I drive a Volvo S40, 2006 with 45K miles. When I take the car out of my garage the AC works beautifully until the car begins to get warm. At about 30 minutes into the driving trip, only warm air blows. If I park anywhere in the sun, the AC does not provide cold air at all. The AC only works when the car is cool. I brought it to the dealer and they said the compressor is shouting off and needs to be replaced. The cost would be $1,130. I was hoping that it was low on refrigerant, which they did not check, and my son thinking that a fan belt gets loose when the car warms up. I would really appreciate your advice. When I went to the dealer it was a cool day. I drove several places that morning and the AC worked for three hours before going warm. Thank you so much!


#2

Go to an independent auto A/C shop and get a second opinion. A/C is sensitive to ambient temperatures and a marginal system will work like that. It bothers me a bit that they condemned the compressor without hooking up gauges, but maybe they heard or saw something that told them that. A second opinion would tell you for sure.


#3

Is there any difference in cooling performance relative to driving speed? Does the AC performance drop off when the engine temperature is rising above normal? And low refrigerant is a possible cause. I would suggest that you get an independent AC mechanic to check it out. Your compressor won’t shut itself off because it needs to be replaced. If the dealership did not check the system pressure and offered no more explanation than was expressed in your OP they don’t seem worth dealing with in my NSHO.


#4

One thing you might try when the A/C quits working is to first make sure the compressor is turning. If it is, take a large fan and direct the air flow through the grill into the radiator. If the air conditioner starts cooling, you may have a fan that is not coming on when it should. I had a similar problem with a 1990 Ford Aerostar. My shop found the problem in this way. It turned out that the fan clutch was not letting the radiator fan come up to full speed. It turned fast enough that the engine didn’t overheat, but not fast enough to circulate sufficient air through the condenser.


#5

I’d toss a small can of refrigerant into it and see if the A/C improves any. You need to be mindful of accidentally overcharging the system, which is why I specified “small” can.

If cooling improves, suspect a refrigerant leak.


#6

Thanks Busted Knucles and Rod Knox. Can you recommend an AC specialist in the Jamaica Plain/Boston/Dedham area? I will take it for a second opinion. I don’t really know what led to the diagnosis exactly. Also when they gave me the proposal, I was pretty sure he said that recharging the refrigerant was not included, but when I declined the service they definitely said a recharge was included in the cost. I had asked if changing the compressor would definitely solve the problem and he said he was 95% sure it would, but the next thing to check would be the refrigerant and then the piping to the compressor. The driving speed does not seem to change anything. I drive mainly in the city but the highway is the same. The car engine has never over heated. Thanks for your advice!!!


#7

Triedaq and MeanJoe, Thanks! Those are both good suggestions. I’ll give them a try.


#8

It’s near impossible to make much of a guess at an A/C problem without high and low side pressures being known, etc. The odds of the compressor being bad are very, very slim in my opinion.

If the A/C works beautifully until the car gets warm then I’d say the compressor if fine. The A/C getting warm later on could be due to a pressure fault, icing of the evaporator, blend door problem, and while I’m not familiar with the setup on this Volvo, some cars have a sun sensor that will prevent or allow certain climate operations; all depending.


#9

OK4450, that is exactly it! It does work beautifully starting out. The day I brought it in it was 60 degrees with light rain. Upon leaving the dealer I figured they must have fixed it and not said anything because it blew COLD for a couple of hours. Conceptually, it just seemed wrong to start with the most drastic of measures, ripping the compressor out and getting a new one. There doesn’t seem to be a good explanation, unless, I just did not understand them properly, for doing so.


#10

The belt that runs your compressor is turning all the time. What makes the compressor engage when you want it to is the part on the front of the compressor called a clutch and coil assembly. A switch turns on the coil and the magnetic field it creates engages the clutch and turns the compressor. I have seen a clutch work fine at 60* but after running for an hour at 85* go “open circuit” and fail to engage the compressor. The only part at fault may be the coil, but to replace it often requires removing the compressor from the car and then the associated disassembly and reassembly of the compressor. At this point it only makes sense to replace the compressor assembly complete with a new one rather than repair the compressor and offer no warranty on the actual internal workings of it. The difference in price may only be $100 or so.

I have no idea if this is in fact what’s wrong with your car, but it’s one reasonable explanation as to why the compressor needs replacement.


#11

There was a time when things were simpler that tracking an A/C electrical problem down could pretty much be done with a test light and eyeballs.
With modern electronics the number of electrical roadblocks put in the way of electrical power making it from A to Z has increased dramatically due to relays, compressor modules, and a plethora of switches.

I do agree that an iffy compressor clutch coil could cause a problem like this. I also wonder why with an A/C complaint they did not throw the gauges on it to see what’s going on when the compressor is or was engaged.


#12

Asemaster, Thanks for your reply. I decided to replace the compressor. I was told that the problem was the clutch, just as you describe, and also that the internal wiring was most likely damaged too. They said it would cost nearly the same to fix / replace the clutch, and if the wiring inside was faulty then I would still have trouble. While it seemed so wasteful, it has been a pleasure using the car during this summer weather we are having! Cheers! Scalesey


#13

I had the same problem. I noticed that the engine was running a little hotter than usual and checked the coolant. It was low. The car wasn’t over heating but running warmer than it usually does. I added 3 16 oz bottles of water and that fixed it. Watch your gage, if you have a light then check the water level bofore you start it. If it works at all it’s not in the ac. You can test the clutch by turning the ac on and off while it’s running and listen for the clicking when it turns on and off. If the engine is getting too hot it will shut down things to lighten the load and help cool it down.