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new to me audi a4

98audiA4 on Tue May 25, 2010 12:10 PM User is offline

Year: 1998
Make: audi
Model: a4
Engine Size: 2.8
Refrigerant Type: 134a
Ambient Temp: 85
Pressure Low: 56
Pressure High: 140
Country of Origin: United States

i recently got an audi a4 that was in pretty good shape but had been neglected for a period of time (stopped driving it because of a newer vehicle) but owner claims he started it from time to time. the AC does seem to work to some extent but vent temps aren't terribly cold. if driven for a while it eventually gets the temps down which to me indicates that it may be LOW. I took readings in 85 degree heat and got a low side of ~56psi and high side of ~140psi. The low seems too High and the High seems too low but from what i've learned here the compressor is a little goofy in that a valve controls the pressure. what sort of corrective action should i be taking? Normally I'd think the compressor was bad but maybe the control valve is causing the pressure problems? Maybe I need to drive it more? Maybe it *just* needs a little boost?

Edited: Tue May 25, 2010 at 12:14 PM by 98audiA4

HVargas on Tue May 25, 2010 12:46 PM User is offlineView users profile

What was the static pressure at 85*? That high side seems pretty low so first thing I would do is have the refrigerant recovered and have the proper amount charged so you know you are starting with a good full system. Then you can start diagnostics from there.


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98audiA4 on Tue May 25, 2010 12:52 PM User is offline

static pressure in the HOT engine bay was ~100(psi). ambient temp was ~83(F)
thanks, may end up doing that unless something in this system is a common failure.

98audiA4 on Tue May 25, 2010 9:26 PM User is offline

Didn't have time to hook it back on the machine but I did have a plain can of r134a and a hose layin around so for laughs I put 10 ounces in and my outlet temps dropped. Low side still was around 55 at idle high side still about 140. If it doesn't improve with a few more ounces I'll vac it out and report back. Probably not the best solution but its almost 90 here and I've got so much to do.

98audiA4 on Mon May 31, 2010 8:52 PM User is offline

alll right update time. VAC'd it down and replaced orifice ($2 at advance, might as well). then I vac'd it for about an hour and it held steady so I put in 1oz pag-46 and 24oz of refrigerant. guess what? no change. low side 50 high side 140 outside temp 80 vent temp 60 engine RPM 2000.

bad compressor?

HVargas on Tue June 01, 2010 3:24 PM User is offlineView users profile

Was there any debris on the old orifice tube? How do the lines feel going to and from the evaporator?


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98audiA4 on Tue June 01, 2010 4:32 PM User is offline

orifice tube didnt look brand new but it certainly wasn't clogged with metal or anything. the line entering the evaporator reads ~60 on the IR therm so i think the air box is extracting the best that it can. i'll try to take a good picture of the orifice tube later on

98audiA4 on Tue June 01, 2010 8:51 PM User is offline

i had already stopped at a jy (excuse me, auto recycler) on the way home and picked up a 97 a6 compressor. i removed my compressor (after recovering the last charged) and used a drill to spin it and not a drop of oil came out. the recovery machine did not show any recovered oil so that's a little interesting. i flushed about 4 oz oil through the "new" compressor in increments (it only took about 1.5 oz at a time) and after running it all out added about 3-4oz of PAG-46. I reinstalled it and charged 750g into the system (the machine says the hoses hold 3-5oz) so there may be slightly less than 700g in the system. (after vac'ing for 60 minutes)

Now the good news. The low side pressure came down from previous (55-60) to ~41 and the high side at first was ~220 but settled around 160. ambient temp was between 80 and 74 (car said 74, machine said 81). Vent temps are now 41-43 degrees on HIGH! YES! The machine probe said 43 the little analog instant read i had in the vent too said about 40-41 which is way better than 60.

Perhaps the old compressor is fine but because of lack of oil it could not produce the proper pressures? not sure and it certainly isnt worth swapping it out again but it appears that this issue is now over.

btw, i'm using an old snap-on act-4100 that i picked up off of craigslist a couple years ago. the PO said it worked fine but he wasn't buying any more R-12. After changing the hoses over and evacuating the recovery tank (it was empty anyway) it's worked quite well for vacuuming out 134a.

Chick on Wed June 02, 2010 6:56 AM User is offlineView users profile

Apparently your old compressor was bad, poor suction and dischagre, don't bother swapping it back...JMO...

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98audiA4 on Wed June 02, 2010 7:16 AM User is offline

i'm pretty sure you're right

98audiA4 on Mon June 28, 2010 3:14 PM User is offline

sorry to dig this back up, but can anyone let me know what the correct OT size is? i've seen it on four seasons, rock auto, and FJC as three different sizes. my cooling while good, could be better. I got an OT from advance that is .072 but on 4 seasons it says its listed .0605-.0635 and FJC says .057. I get the impression that having the RIGHT size or perhaps slightly smaller would be best but I don't even know what the right size is.

98audiA4 on Mon July 19, 2010 8:36 AM User is offline

One last final piece of info on this car. The main control valve IS adjustable from the outside with a flat head screwdriver. While monitoring pressures turning the valve clockwise (closing) raised pressures and turning it CCW lowered pressures. With the valve all the way open (CCW) low side dropped into the low 30s and started giving me sub 40 degree vent temps. Very nice.

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