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help! ac system just stops after a day or 2....

brax on Thu August 20, 2009 7:20 PM User is offline

Year: 2001
Make: audi
Model: s4/a4
Engine Size: 2.7twin
Refrigerant Type: r134a
Ambient Temp: 90
Pressure Low: 35
Pressure High: 250
Country of Origin: United States

ok if anyone can help that would be great! details:

2001 audi s4 vw/a4 similar ... lower ac hose scrapped the ground and got a hole, left the hose damaged all winter, never ran ac or tried,

bought a new hose and replaced the orifice tube reg/filter.... recharge, AC blows cold from anywhere to a hour to 3 days then just stops, hook the gauges back up and it acts like

the compressor is not working, so vac'd rechecked the orifice tube filter, all is fine, same symptoms, replaced the receiver drier, did a 30 min vac, same symptoms, good for a

day or 2 then just stops, usually over night, pressures are fine, nothing leaking....

the oil looks clean, no black death....... when we recharged the system originally, we add'd oil twice or three times not knowing that the system probably did not need it "i was stll

learning the machine and how to work on ac systems" maybe 1oz at a time, i have vac'd the system probably 12 times since then and have not add'd oil again,

if anyone has any ideas i would much appreciate it, thanks

Edited: Fri August 21, 2009 at 4:53 PM by brax

mk378 on Thu August 20, 2009 10:47 PM User is offline

You probably have a SD7V16 compressor, they do this. It's a variable displacement compressor that is supposed to slow down based on the low side pressure to prevent over-cooling and freeze up. But the control valve can get stuck at zero displacement which means the compressor spins but won't pump regardless of pressure. Typically it is permanent when that happens though.

Edited: Thu August 20, 2009 at 10:48 PM by mk378

brax on Thu August 20, 2009 10:49 PM User is offline

whats the solution? replace the compressor? ( anything i can do?

thanks for the reply!

brax on Thu August 20, 2009 11:19 PM User is offline

one on ebay labeled 7SBU16C prolly the same comp with a diff bolt pattern huh? same type design?

/link edited out/ sorry

Edited: Fri August 21, 2009 at 4:53 PM by brax

knightgang on Fri August 21, 2009 7:17 AM User is offline

See note at the top of the page, no auction links on this board. This board is sponsored by the great guys at AMA ( Take a look at them for a new compressor.

Peter_Coll on Fri August 21, 2009 8:42 AM User is offlineView users profile

R32? Are you sure? That is not the easiest refrigerant to get.

brax on Fri August 21, 2009 10:31 AM User is offline

no i am not sure, r12? whatever the normal is now, my bad

HVargas on Fri August 21, 2009 11:30 AM User is offlineView users profile

Your car uses R134a refrigerant. You are indeed going to need to replace the compressor and I won't even start in on anything off eBay. We have 2 options, new and rebuilt. In your case we can get a new one from less than a rebuilt and a very good price as well. Feel free to email us for details.


When considering your next auto A/C purchase, please consider the site that supports you:
Contact: Arizona Mobile Air

brax on Fri August 21, 2009 11:39 AM User is offline

gotcha, well thanks for the reply, hopefully i can make it through the rest of the summer, i have to pull the front clip to access the ac comp, yeah i meant to say 134a, machine was setup already with its own tank

so i guess the comp is locking up? no temp fix's? flush? thanks

iceman2555 on Fri August 21, 2009 3:10 PM User is offlineView users profile

It is doubtful that this is a compressor issue. The compressor is definitely working...look at the pressure difference. It could be an control valve issue. But since the system was open to the atmosphere for such a long period, I would check the TXV. It is quite possible that the TXV is not functioning correctly. Movement of pintel restricted by possible internal corrosion or other internal problems due to element exposure may result in a 'false' signal to the compressor control valve.
It seems as if there is a good possibility that the system is seriously overcharged with lube, use a good flush, clean the system, change the TXV and recharge and test system.
Good luck.

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Thomas Jefferson

mk378 on Fri August 21, 2009 3:21 PM User is offline

What are the pressures when it stops working? Are you sure the compressor clutch still engages when it is not working? I was thinking this could just be a simple leak out, that's what you usually think when someone says they charge it up and it only works for a day or two.

brax on Fri August 21, 2009 4:24 PM User is offline

awesome guys, i will google what the hell txv is lol and try and figure it out, yes pressure never leaks out, compressor still runs, just blows hot air, when i hook the gauges up it acts like the comp is not working even though it is......

no the only way it works again is if i VAC the system, the freon never leaks, strange issue ..........

mk378 on Fri August 21, 2009 4:47 PM User is offline

You get all the cooling from the last few oz of refrigerant. There can be considerable pressure but it won't work. Also since refrigerant condenses into a liquid under pressure, you have the same static pressure with one drop of liquid in the system as with a full charge. But you sound like you've actually tried adding more refrigerant when it is not working.

Again, what are the pressures when it is not working?

brax on Fri August 21, 2009 4:52 PM User is offline

to be honest i cant remember what the exact pressures were when the a/c stopped blowing cold, but the readings were the same as with the comp running or off, the readings would slightly/barely move... like the comp was doing nothing even though it was on.....

mk378 on Fri August 21, 2009 5:02 PM User is offline

You should go back and measure again, it will tell a lot.

If the TXV is blocked, there will also be no pressure change for a long time after stopping the compressor, because there is no flow through the system. But the low side will be around 20 like it should be (variable compressors should never go below 20). If the compressor is not working, low side will be higher.

brax on Fri August 21, 2009 5:08 PM User is offline

cool deal, i am going up to the shop tomorrow and will report back with the readings, i appreciate all the help guys...

i hope i do not have to replace the compressor because it requires pulling the front clip on this model, "not that i have not pulled the clip already 5-6 times lol"

where is the TXV valve located at? any ideas? is it internal on the compressor itself?

come to think about it, there was one 2 wire plug from the front clip that ran to the radiator/condenser area.. i have scanned with obd software and i am getting no codes for the engine / climate control , also the fans are functioning properly with the a/c running ... so i am not sure if i left something unplugged or not, i cant find the other side for the life of me

brax on Fri August 21, 2009 5:10 PM User is offline

ok.... if i am not mistaken google says the TXV valve is the same as the expansion valve, on my car it has the orifice tube expansion valve which i have replaced already..

also the a/c was working fine until i got a hole in the line for the record.

knightgang on Fri August 21, 2009 8:12 PM User is offline

TXV is Thermal Expansion Valve. You will either have an OT or a TXV on a single A/C system. Dual air systems may have both, one on each evaporator.

brax on Thu August 27, 2009 12:32 PM User is offline

hey guys,

sorry for no updates yet on the pressure readings, the AC has been working fine the last 3-4 days, "its random"

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