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I drive a 2013 Chevy Sonic.

Basically, the air conditioning does not blow cold air if the car is idling, only when in motion. It seems to blow the coldest during long periods of driving fast, such as on the freeway. Once I have slowed down significantly or stopped, the air blowing out gets warmer and warmer. If I leave the AC on cold long enough (more than about five minutes) while staying slow enough (idling or driving >10mph during heavy traffic), then the engine overheating warning appears on my dashboard:

temp warning

When this happens, I stop, open the windows, and turn on the heat to max. This typically makes the warning go away quickly, within 20-30 seconds. The warning will not come back unless I return to idling with the cold AC on. This has happened at least half a dozen times in the past year, so I typically just turn the AC off when going slow to avoid it.

The first time it overheated I refilled the coolant, but that didn't end up having any noticable effect.

Is there anything I can check on to try to figure out the source of this problem? Is it something urgent that I should get checked out right away?

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    Do your radiator fans turn on when the car is stopped and the engine temperature is hot? The fans help dissipate heat for both systems, that is the only common link between the two.
    – user3188168
    Jul 12, 2016 at 18:36
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    You mentioned that you "refilled" the coolant. Has the level been dropping over hours, days, weeks of driving? Have you noticed coolant on the ground below your car?
    – StephenH
    Jul 12, 2016 at 19:40
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    @StephenH it is plausible that a slow leak is to blame, but loss of coolant could also be the result of overheating due to over-pressurization
    – Zaid
    Jul 12, 2016 at 19:49
  • @Zaid good point. But either way, that piece of information could be helpful for determining the root cause. Coolant level could be especially critical if a more serious issue is present (coolant leaking into engine) though I would expect a rougher ride and/or misfires.
    – StephenH
    Jul 12, 2016 at 19:51
  • @StephenH oh I agree
    – Zaid
    Jul 12, 2016 at 19:53

5 Answers 5

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A few things spring to mind:

  • confirm radiator fan operation (per user3188168's suggestion)

    The fans are vital in ensuring air flow across the both radiator and A/C condenser when the car is stationary or moving slowly.

    A few things could cause them to not run:

    • blown fuse(s)
    • bad relays
    • wiring open
    • lack of command for the fans to turn on from the ECU (typically governed by a engine coolant temperature sensor)

  • belt slippage with the A/C engaged

    It is unlikely that this is applicable to your case though, since this would cause issues with alternator charging and loss of power steering assistance.

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    Sorry this response is so late, but it was the indeed the radiator fan! It was not turning on, and the whole fan had to be replaced. With a new fan, both problems (AC and engine overheating) have gone away. Thanks for your help!
    – Robin
    Aug 23, 2016 at 17:40
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Engine overheating is not related with A/C misoperation.

Engine overheating while idle:

  • Bad timing
  • Low cooling liquid level
  • Dirty radiator (outside but also inside)
  • Radiator fan malfunction
  • Air in the engine cooling system (it WILL overheat the engine and very fast)
  • Low oil level

I would: drain all cooling liquid from engine by uncorking the radiator's valve underneath it. Watch for any dirty, etc. If no dirt, then cork it up again and add new liquid, being sure to squeeze the thick hoses from engine to radiator, like a hand pump, to evacuate any trapped air there.

If I get some dirty out of the radiator, I would plug the garden hose to the cooling recipient and let water fill and run out for a while, also squeezing the hoses, then cork up and refill as appropriate.

Now, a/c not working well in idle:

  • Loose belt (won't turn the compressor enough in idle, therefore under compressing)
  • Refrigerant gas wrong pressures (too low to cool but still not too low to make ice. Yes, low refrigerant gas will produce ice in the evaporator, ie, inside the car)
  • Bad a/c fans (not extracting the heat enough from the a/c condenser, ie, the outside "radiator")

If the a/c cycles (turns on/off itself) then it can be the pressure sensors working (either low pressure, or high pressure sensors).

However: engine overheating is an engine problem (timing or engine cooling system, or even low oil level) NOT induced by the a/c system.

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No i have the same problem with mine and i know exactly where the problem lies. T\The connector to the fan will com loose or if you take it off you may even notice that it is burnt. sometimes it will run and you never have a problem while other times it will kick out some serious heat. thats because your fan stops operating. I had to take it apart and clean the connector cause it had some kind of gunk on it. Still have engine temp higher then normal but dont have the heat anymore. I might have to replace the whole wiring harness or at least splices new connectors in.

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Sounds like you're having a thermostat problem for the engine overheating. Also could cause the AC to stop working if the heat from overheating gets to the AC pump.

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Relpace the cabin filter and clean the intake car engine air conduct.

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