A/C compressor cut out in traffic

Yesterday I'm driving home and in traffic. Temperatures were in the 80s but the readout on my dash said 97 degrees on the highway. Had my A/C set to 70 degrees and all of a sudden the temperature changes and the air begins to feel a lot more humid. I bring the temperature down to 66 degrees but still no change. I noticed the coolant temp was in the hash mark between 180 and 250 which was warmer than the usual 180 but not anything to be too concerned about. In any case it stayed this way for the next 5 minutes while in traffic but once I got moving again the compressor kicked back on and everything seemed fine. Is this behavior normal? Should I get the system checked out? I've had this car for years and in much warmer temperatures and haven't encountered this before.

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Wouldn't be a bad idea to get the A/C system checked. Could be low on refrigerant. If it is there's a leak in the system. Before you book the car in for this be sure the radiator fans are working ok. They should be on low when the engine is running and the A/C is on (the snow flake is lit). Also, check the fans come on when the engine gets warm. Drive around town until the engine is fully up to temperature. Oh, leave the A/C off. Once the engine is up to temperature and has been a few minutes back at home in the driveway let the engine idle until the fans shut off, if they are on. Then raise the RPMs to 1000 and hold until you hear the fans (or fan) come on. Check that both fans are running and both are blowing out the same amount of hot air -- and it feels the same temperature. If you find nothing of concern with the fan check out then have the A/C system checked. Even if you do find a fan not working I'd still have the A/C system checked out. If the system is low on refrigerant using it can damage the compressor. Compressor oil in the system is carried along by the refrigerant. If this is low the compressor can be damaged from lack of sufficient oil.

I had a similar issue where my car wouldn't keep heat unless I was driving. Anytime I was stopped it would blow cold air. Turned out I had a bad radiator cap (the seal was damaged). Replaced it and burped the system of any air. This may not be your cause, but it sounds like there is air getting into the system some how or something isn't working properly. Definitely get it checked out and let us know what you find out. If you want more info on the system you can read up on it here . -Luccia

I would say your system is cutting out on high pressure, most likely due to the cooling fans not coming on when they should. On Audi's, the ignition switch fails and causes the load reduction relay not be picked up, which powers the cooling fans. You don't notice it until you figure out that your low beams also don't work. Once you drive away, there is adequate cooling to lower the system pressure with no forced cooling. It's probably something simple, but almost for sure a high pressure cutout of the system.

Ditto for checking you stage 1 (low speed) fan operation. Very simple. Can do with car cold, start car and put the A/C on. In less than one minute you should be able to hear and feel both fans operating on low speed. Follow Macsters instructions for checking the fans. Just went through this but didn't correlate the less than ice cold A/C with my stage 1 fan speed not operating. Had the fan resistors replaced yesterday and when we took her out for a test drive the mechanic commented "now you've got ice cold air". I just looked at him and asked if the radiator fans had something to do with the A/C and he just smiled and said "of course". I left it at that figuring I had already showed enough of my ignorance. Anyway, now my temp is back to never rising above the middle of the zero in the 180 and my A/C works fantastic. One less imaginary problem to solve for. Hope it is as simple as this for you as well. FYI - OEM resistors cost me $181.00 shipped for the pair from Sunset Porsche.

I think everybody is on the right track. You need to check the operation of your cooling fans and make sure they are running properly. Also, might be a good time to do the radiator cleaning. You said that the temp gauge got to the 215 mark...that's pretty hot. I've never seen mine hit that point, even in 90+ degree weather with the AC on. When you turn the AC on, the fans should automatically go to stage 1. Then when things really warm up they should go to stage 2. I've come in the garage from a stop and go run with temps running a bit on the right side of 0 (of the 180) and the car sounds like a hovercraft about to take off. Maybe even your DME determined things were too hot to engage the AC compressor. It does create quite a load on the engine, and if the DME senses things are too hot it will not engage the AC compressor. Check fans and clean radiators.

Thanks everyone! I'll check it out tonight. I know in the past the fans are pretty loud on hot days but hadn't realized it lately. I will report my findings!

My money is also on non-operating fan(s).

Fans were running when I pulled up to the garage last night. Now they didn't seem to be on full-blast mode but they were absolutely running. I hadn't really been in traffic which is why they probably weren't in high speed mode. Temps stayed at a touch above 180 for the entire drive. In any case I made an appointment for an A/C check next week. Hopefully it'll be something simple (and inexpensive!).