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When the temperature outside is cooler, say less than 80°F, and I turn my AC on, everything works great and I get nice cold air in the car. In the late afternoons however when the temperature is above 90°F, I get cold air for 2-3 minutes then I hear a 2-5 second groan followed by about 5-10 seconds of warm air and then everything returns back to normal again with cold air blowing for another 2-3 minutes before the cycle repeats.

Anyone have ideas of how I can determine what is wrong?

The AC is the type where you just choose a fan setting between 0 - 4 (no thermostat to keep it at a set temperature). No work has ever been done on the AC.

I can visually see the AC compressor turning on under the hood when I turn the AC on in the car. Also worth noting is that my car sat for 3 weeks without being started while I was on vacation and this problem developed only once I got back and started driving it again.

Thanks for any advice.

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    Is the AC an auto temperature selection (ie: you set to 72° and it's supposed to keep it there) or the dummy knob where you have to adjust as needed? Also, which VW model and engine? – Pᴀᴜʟsᴛᴇʀ2 Jul 30 '15 at 10:30
  • Sounds like the AC is cycling on and off. Any work performed on the AC? – Zaid Jul 30 '15 at 10:45
  • Went ahead and updated my question with additional information. – Bert Wagner Jul 30 '15 at 11:21
  • It may be a problem with the condenser. A/C works by compressing a vapor into a fluid, and then cooling the fluid, which has become hot as per the combined gas law, in the condenser. As this cooled fluid is depressurized, it becomes even colder, allowing you to generate cold air. If there is a problem with the condenser, and it can't dissipate heat quickly enough, then the depressurized air won't be any cooler than it was when it was initially pressurized. – alexw Jul 30 '15 at 23:13
  • It is also possible that the "orifice tube" is actually getting iced over, and thus blocked. See the section "AIR CONDITIONER PROBLEM: INTERMITTENT COOLING": aa1car.com/library/ac98.htm – alexw Jul 30 '15 at 23:19
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I have seen this on a VW Passat. The problem in that case was a malfunctioning condenser fan. In cooler weather ambient temperature and air flow provided sufficient cooling to keep the high-side pressure within limits. At higher temperatures, there was not enough cooling, and the pressure went high enough to trip the high-pressure switch, at which point warm air came from the vents. So I would suggest a quick and easy check is to make sure that the condenser fan is running.

  • Thank you! Turns out the larger of my two radiator fans had broken and just needed to be replaced. – Bert Wagner Aug 24 '15 at 12:02

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