Automotive Air Conditioning Information Forum

Hey..long time no chat on this forum. Gotten some newer vehicles that ran great (and blew cold A/C) for years, now having a no A/C issue at stand still/idle. It cools the car once moving.

2007 Audi A4
Vent temps - unknown, but warm sitting still.
ambient - 76°F
low side - 62 (that seems really high)
high side - 125 (that seems low)
RPM = idle

The compressor is cycling..no noticeable pressure drop on the low side for the 10 seconds the compressor runs..not much condensation under the car sitting in the driveway. Once we start driving it pumps cold air in the cabin..at a traffic light and in the driveway (idle) it gets warm again.

Thanks...good to be back.

No clutch on that compressor, so it is not cycling.

Looks to be low on charge. Recover it & charge the correct quantity of refrigerant by weight. Electronically controlled variable displacemnt compressors are sensitive to charge levels, so topping off is a no go.

Add some dye before you charge it.

Thanks for the reply. I know the last time this unit received service was when the timing belt was replaced 20k miles ago. Until this weekend, it has never had a problem.

Thanks for the info on the compressor. These newer ones are getting too complicated for me...I might have to take it somewhere...I don't have the means to actually measure...I can just do a SWAG at how much is left in a 12oz. can. Maybe one day I'll get a scale and a larger container so I can track the weight more accurately.

So, what was happening when I assumed was the compressor cycling? I did have a change in RPMs, and noticed extra load on and off the engine about every ten seconds or so. My wife laughed at me when I said I need to figure out a way to tape the gauge set to the windshield and drive down the road to see those numbers. I have done that on my old Civic before.

The system will try to run at a low charge, but it goes to full stroke & sees an out of range low pressure. It is not returning oil very well at low charge either.

You can add some refrigerant to stretch another month & get past the worst of the heat. But it is only guesswork. Watch the high side, add in small ammounts. Do this at 1500+ engiene RPM. Do not let the high side go beyond 2.7x ambient temperature. So if it is 78F ambient 78 x 2.7 =210 That is your max high side. Use 2.5 as a target.


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