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Old 08-09-2018, 10:39 PM
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Join Date: Aug 2018
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Question 2008 Audi A4 Overheating / AC problems

Picture of engine load at idle with A/C on. Compressor must be switching on and off.
  • 2008 Audi A4 3.2l Sedan
  • About 85,000 miles
To begin, the other day I noticed that my ac began hissing and then I'd lose cold air in the cabin. This happened in cycles, and would finally stop cycling between cold and hot air once I got above like 30mph. Taking the advice of many and google, I decided to go and buy a bottle of refrigerant with a gauge, to check the pressure. I then noticed that when idling with the A/C on, the pressure would fluctuate from high to very high. So, no refrigerant was needed, there was no leak, like I thought there was. Immediately after checking the pressure in the parking lot of the autoparts store I got in the car and noticed the coolant temp rising considerably. I drove for a tiny bit before pulling over due to the coolant alarm going off. I turned the car into the acc position, and turned the a/c off. I popped the hood and saw that both radiator fans (electric) would turn on and off constantly, even when the engine was almost red on the temperature gauge! The temperature of the car would not go down so I said f**k it and began to drive home. Once moving, the temperature dropped to normal within a minute. Now I'm curious so I turn the a/c back on and the same overheating happens. I turn the A/C off and drive home. I pull out my obd scanner and notice that while idling with a/c the engine load would double for a few seconds (cold air blew), and then it would go back to normal (hot air blew).

My conclusion:
Due to the two front fans not engaging when they were supposed too, too much pressure would build up in the a/c lines and cause the compressor to have alot of stress, which meant it began to turn on and off and put alot of load on the engine. This engine load along with lack of proper cooling led to overheating, which was eliminated when natural air blew through the radiator from me driving at speed. The fix? I have no idea. Right now I'm guessing it's the temperature sensor or the fan control unit.

Other notes to be considered:
  • -When I got home I smelt burning clutch (I have an automatic so it was most likely the fan on the A/C compressor)
  • -For whatever reason when it overheated they stay in a much lower gear, shifting up at twice the rpm than normal
Please, I will take any help! I'm not prepared to spend thousands at a garage!

Below is a picture of the engine load at idle with A/C on. Notice the compressor switching on and off (assuming due to high pressure in lines).
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