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AC quits when stopped and got differing opinions from 2 shops

My AC quits working when in stop and go traffic or at a long light. Comes back on when I get going again after a minute or 2. One shop says thermistor another says thermostat is faulty causing engine to overheat. Not sure who to believe. Car gauge never shows engine to be overheating. Can someone help me? 2007 Hyundai Tiburon

Has anyone checked the state of charge of the AC system?

Low refrigerant level in the AC system can cause the problem you describe.


Both shops did. AC runs great. Very cold. Just turns off if I’m stopped too long.

If the engine shows no indication of overheating, then there’s not a problem with the thermostat or the rest of the cooling system.

The AC system does have a thermal limit switch. What this does is, it senses if the engine coolant temperature begins to increase while the engine is at low RPM’s with the AC on. The AC control module then shuts off the compressor so the heat coming off the condenser is no longer going into the radiator. This then lowers the coolant temperature.

The next thing to have checked is if condenser in front of the radiator has a lot of debris collected on it. As this can restrict the air flow thru the condenser/radiator.

If that doesn’t appear to be the problem, then it could be the thermal limit switch.


That makes more sense than anything I have been told so far but I would think both Firestone and Christian Brothers would have checked that. I may have to google it and check that myself. Looks like I need to try shop #3. 3rd times a charm right? Any suggestions on a good shop? lol Thank you for your help.

If it just started doing that, it may be the electric cooling fan or its relays. There may be 2 fans, one that should run whenever the AC is on and the other to run just when the engine gets too hot. If it doesn’t run check the fuse and relay.

If there is just one fan, check to see if the fan runs all the time when the AC is on but the engine is cool. Again, check the fuse and relay. The single fan may work just fine to keep the engine cool but is not getting turned on when the AC is on and should

Finally, did you just move to a new state that is hotter than you old one? I had to add an additional fan in my 10 y/o truck (with an engine driven fan) just for the AC condenser to keep cool air blowing while sitting in traffic in a hotter climate. You may need to add one, too.

It was a new thing, it started last summer. Living in Dallas area so it gets HOT, and I bought the car here. But my car used to stay cool all the time. You can actually hear and feel the engine RPMS change when I turn my ac on and off. I noticed this is also happening when it quits cooling then starts cooling again. It gives me the impression that something is turning off when I am stopped but turns back on when I get moving again. Like something is overheating and cools down when I get moving. But I don’t buy that it is my engine. And I do appreciate these comments.

@HeyLisa …the biggest problem that I see here is that you have been taking your vehicle to Firestone and Christian Brothers. They are not AC specialists by any means. Go see an independent AC shop and they will get the job done. BTW…I love your name.

HeyLisa, please clarify one thing. When you stop at a light, are you saying that air stops blowing out of the vents? Or are you saying that the air continues to blow out of the vents but it isn’t cold?

If you are saying that the air stops coming out of the vents, then this isn’t a problem with your AC, but just a problem with the blower fan. That could be why one shop mentioned a resistor-type things.

Yes, @Lisa. What is meant by “AC quits”

Sorry, should have been more descriptive. AC quits blowing cold air but is still blowing air.

This should be easy for a shop to figure out but I’m not sure how you could do it yourself or if we can help you over the web. Any shop with A/C equipment, a decent scan tool (not a fault code reader), a complete wiring schematic, and a good voltmeter should figure this out quite easily. Any shop without these things will just be taking educated guesses. (Technically I wouldn’t even call it a shop.)

The fact that the temp gauge never goes to hot isn’t necessarily an indication that there isn’t a cooling system problem either. The car should cut the A/C before it overheats, not after. Some cars disable the A/C for any kind of cooling system problem, even if it means the engine is running too cold.

There isn’t enough air flowing over the little radiator the AC uses - the condenser. The electric cooling fan should be running when the AC is on. Open the hood, start the engine cold with the AC off and check to see if the electric fan behind the radiator is running, it should be off. Now turn on the AC, the fan should now be running even though the engine is not fully warm. If it is not, the relay is likely in need of replacement.