Automotive Air Conditioning Information Forum (Archives)

prof_chaos on Wed August 15, 2012 11:12 AM

Year: 1998
Make: Audi
Model: A6
Engine Size: 2.8
Refrigerant Type: R134a
Ambient Temp: 70
Pressure Low: 30
Pressure High: 350+
Country of Origin: Germany

I think it might be the electric fan. I just overhauled my AC system with a new compressor, new condenser, new accumulator and new orifice tube. I flushed the lines with Dura II and a flush gun and vacuum it down for a total of around 3 hours. There was some debris on the old orifice tube, which I wrote a thread about here http://www.autoacforum.com/messageview.cfm?catid=2&threadid=23876

Now, while charging up I am seeing the pressure get too high on the high side. So far I have only added 9 ounces (capacity is 28).

With the compressor engaged, I am seeing around 30 on the low side and the high side slowly ramps up and up - I have let it get above 350 then switched the system off because I was afraid of damage. I am not sure at what pressure the cut-off switch should stop the compressor but I didn't want to take any chances.

My car has 1 viscous fan and 1 electric fan. The viscous fan works (engine never runs hot no matter what the weather) but the electric fan does not seem to come on at all, even with the AC running. I have been told it should always run when the AC is on. Could that be the reason for the high pressure on the high side? I know a restriction is possible, but I did flush everything and put a new orifice tube in, and also I thought a restriction would likely cause a low reading on the low side as well as a high reading on the high side?

Anyway I am just looking for any other suggestions besides the fan...I will work on getting the fan running later and see how it goes. Thanks!

GM Tech on Wed August 15, 2012 11:21 AM

Quote


. Could that be the reason for the high pressure on the high side?



YES

-------------------------
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......

AutoCool on Wed August 15, 2012 1:24 PM

Hi, your car has a trinary AC pressure switch on the condensor. It's designed to not allow compressor operation at pressure less than 30 psi, it starts the auxillary fan at 223 psi, and breaks power to the compressor clutch at 441 psi. The switch could be bad, or maybe your fan is bad. Check fuses and fan relay and jump power directly to the fan to see if the fan itself is trash.

Fuse should be 40 amp drivers footwell, relay is under the steering wheel. I believe the relay is marked 214 (or 373?) should be 2 of them. Good luck.

prof_chaos on Wed August 15, 2012 2:05 PM

Quote
It's designed to not allow compressor operation at pressure less than 30 psi, it starts the auxillary fan at 223 psi, and breaks power to the compressor clutch at 441 psi. The switch could be bad, or maybe your fan is bad

Thanks that's great info right there...I searched for hours to try to find out whether there was a second pressure switch, what triggers the fan to run and what the high cut off pressure is. I wasn't able to find any of this out anywhere...you nailed it in one sentence

From what I'm seeing, it looks like the fan - I didn't let it get up even 400 psi, so no reason to suspect the switch yet. But I definitely watched the fan as it sailed past 223 psi and that fan never moved. So I will test the fan and the fuses and relays too.

AutoCool on Wed August 15, 2012 4:30 PM

A bad trinary switch is quite common on the A6, the same switch is also used on lots of A4, A8, S8, and Passat around 1997-2001. There is a schrader valve on the valve nipple, so you won't lose your refrigerant if you remove the switch.

prof_chaos on Wed August 15, 2012 7:27 PM

OK just did some tests...

Fan wires direct to battery = nothing. Motor doesn't turn.

Then I fired her up and monitored the other side of the fan electrical connector. It started out at 0 volts, then when I switched the air con on, it went to 13v almost immediately (pressure was still well below 223 psi at this point, around 150 I think). Anyway it stayed on as the pressure climbed up towards 300. When the air con was switched off, I watched as the pressure dropped and the fan voltage remained on until pressure went below around 200 psi, then it switched off.

I take all this to mean my fan motor is dead, and my trinary switch is switching somewhat on the safe side of the 223 psi threshold you mentioned? Is the switch ok like that or does it need to be replaced? I didn't test the high pressure cut off in case something gets damaged from over pressure.

mk378 on Wed August 15, 2012 11:45 PM

Indeed it sounds like a bad fan. As a final check, test the motor for continuity, and finding it open circuit, replace.

prof_chaos on Thu August 16, 2012 12:00 AM

Well I got it off the car since I posted that and the wiring is good all the way to the inside of the motor, so I am planning to replace it.

prof_chaos on Sat August 18, 2012 12:50 AM

New fan installed...blowing nice and cold! The fan was definitely the problem.

Now it is not blowing as cold as it might...lowest temp I have got from the vent is around 50 in 85 degree weather...so I may have some tweaking left to do. But it's blowing a hell of a lot colder than it was with the seized compressor! Thanks for all the help, it's much appreciated.