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Audi A4 Intermittent Compressor Engage

ldorris on Tue August 27, 2013 10:12 PM User is offlineView users profile

Year: 2000
Make: Audi
Model: A4
Engine Size: 1.8t
Refrigerant Type: r-134a
Country of Origin: United States

Newb here. Bet you pros can point me in the right direction.
Issue: A/C blows icy cold air sometimes (most of the time), but sometimes the compressor will not engage or will disengage. Sometimes I can begin my drive with the A/C working properly, then the compressor kicks off not to come back on. Other times, it will not engage from the start. Usually, if I turn the car off, then immediately right back on (no time for thawing...) it will work again. Both electric fans on the radiator are working properly. The car holds 1.1 lbs of r-134a, but I added some from one of the cheapie Autozone cans with the crummy gauge (do not have accurate pressures to report to you all, but low-side levels were in the green zone on the gauge. Have an appointment for diagnostics in a couple of days, thought maybe I could get a head start on it). It took about 1 lb of refrigerant. The issue does not seem to be related to ambient temperature.
Possible issues from my reading of forums on the topic:
1) Over or under charge of my system throwing hi/low sensors into whack mode and shutting it down (but why is it so intermittent?)
2) Hi/Low pressure (or trinary switch) switch bad - Also, it seems these would be connected to a schraeder valve and would not require evacuating the refrigerant... Is that correct?
3) Fan control module (but both electric fans work properly)
4) Cabin filter issue? (Doubt that given the correction during restarts)
5) Thermostat
6) Compressor/clutch (doubt that since it works so well most of the time, and again... the weird restart thing)
7) Moisture in my system (again, questioning the intermittent nature)
8) Part of the climate control electronics
I'm leaning toward a sensor/electronic issue. What do you think?

Edited: Tue August 27, 2013 at 11:08 PM by ldorris

GM Tech on Tue August 27, 2013 10:37 PM User is offline

you forgot about air gap - how wide is yours?

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

ldorris on Tue August 27, 2013 10:49 PM User is offlineView users profile

Didn't think to check the air gap...

Chick on Tue August 27, 2013 11:49 PM User is offlineView users profile

I think GM Tech hit the nail on the head, clutch gap first.. Then since you added more refrigerant, you will need to have it recovered and recharged properly... Throw away the AZ death kit cans, never charge without "Both" high and low side pressures... Adding refrigerant could seriously overcharge the system and pressure switches can now be shutting it down... But clutch gap first.... Hope this helps..

Get the gap as close as possible without dragging on the pulley....

Email: Chick


Freedoms just another word for nothing left to lose

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