B6 S4 A/C compressor replacement

**Bluecuda97** · 05-07-2015 07:46 PM

I've been a long time lurker but I need a little help that I can't seem to find anywhere. My 2005 S4 is currently at the dealer because the A/C stopped working. The ECON button was staying on and from what I've been reading there is a good chance that its the compressor. If this is the case I plan to replace it myself but I need a little guidance. I have already replaced the serpentine belt so I've been in as deep as the radiator in service position but I realize that it needs to come all the way out along with the motor mount. If anybody has done this or has found any information on how to do this send me a PM -Thanks

**evolution2147** · 05-07-2015 08:34 PM

When the ECON button is permanently on it means that there is no refrigerant in the system and therefore the compressor won't turn on. So it probably isn't an ac compressor unless it is leaking from the compressor itself. If it does need to come out the only main difference from going from the service position to completely off is draining the coolant, power steering fluid, and ac refrigerant.

**Bluecuda97** · 05-08-2015 12:28 PM

Originally Posted by evolution2147

When the ECON button is permanently on it means that there is no refrigerant in the system and therefore the compressor won't turn on. So it probably isn't an ac compressor unless it is leaking from the compressor itself. If it does need to come out the only main difference from going from the service position to completely off is draining the coolant, power steering fluid, and ac refrigerant.

Thanks man, fortunately it was just the high pressure safety switch that went bad. I'm just having the dealer do it since I cant really beat their price.

**Dagear** · 09-26-2017 10:57 AM

Didn't want to create another thread, and this one described my current situation.

I swapped engines last winter, including timing job, valve covers etc. This spring I took it in and recharge the AC, previous owner stated that AC worked. AC worked for about a week, then I checked pressure again and it was low, so thought I had a leak, pulled a vacuum and used DIY can to recharge, worked again for short bit. Last week took it to independent site to have them identify leak. After $90 inspection fee they told me the AC drive shaft wasn't turning.

I jacked it up and noticed that I could move the shaft side to side slightly.

Bottom line it appears that the drive hub of the compressor and disintegrated, since I can push the driveshaft and plate rearward and then turn, then move it forward and engage the splines.

Is this a common failure mode?
Anyone else seen this?

**2004B6S4** · 09-26-2017 12:29 PM

that is the designed failure mode, the drive hub is meant to break away if the compressor seizes up. however that wouldn't cause you to lose pressure, and if it had been broken all along then the recharge wouldn't have made a difference.

sounds to me like your original issue was just a refrigerant leak, but then some time after the last recharge your compressor also went kaput. The compressor is always spinning while the engine is running, and if it has a leak then it's losing refrigerant and oil meaning the compressor would be running without proper lubrication, so that's probably why it failed.

**Dagear** · 09-26-2017 04:45 PM

So new compressor needed obviously anything else?

Other threads make it sound like the shaft itself breaks twists in half

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**2004B6S4** · 09-26-2017 05:46 PM

that's what happened to mine, the shaft itself broke. not sure why...

**Dagear** · 09-26-2017 06:16 PM

Did you replace seals condenser? Dont want to replace unecessary parts byt dont want to do this again

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**2004B6S4** · 09-26-2017 08:05 PM

the condenser can be flushed, the orifice tube (which you may see referred to by other names) needs to be replaced, and the receiver/drier piece needs to be replaced. The evaporator and the lines can be flushed, remove the orifice tube first and flush thoroughly both ways. I also replaced all the o-rings and the pressure switch as preventatives since those are the places it can leak from, but that's not really necessary. you must have a leak in the system already though, so you'd want to find out where it is before you take stuff apart

**Dagear** · 09-27-2017 06:43 AM

2004B6S4,

Thanks for the info, would have PM'd you but thought others might gain from these posts.

Last Question, I can live without AC, my main concern is that since the drive system sheared at rear of compressor, the shaft is allowed to slide in and out of the drive splines. My concern is driving in this situation long term will damage the drive system thus costing more to repair. I can only envision chunks of spline material wearing off and dropping into the oil.

I have seen other posts that state others have driven in this mode but not sure if they damaged their drive components.

**2004B6S4** · 09-27-2017 07:48 AM

I'm sure that's a valid concern, not sure how likely it is to happen. if it does, nothing will end up in your oil though. the drive shaft goes into the middle of a sort of "socket," there's an oil seal around the outside of that socket but the inner part where the shaft goes is just a dry chamber, nothing gets from there into the motor. I drove with my shaft broken for a long time, it made an embarrassing amount of noise and tore up the coupler end of my compressor, but it never disengaged from the splines and didn't damage them.

**roboto_1337** · 09-27-2017 08:33 AM

is it possible that the shaft has backed itself out from the compressor? see if you can hold the shaft still while engaged on the splines and thread the other end into the compressor farther? if it's backed out it won't take much torque to turn the hex end.

**Dagear** · 09-30-2017 06:00 PM

Shaft is still solid and I can move shaft and coupler a small amount

Thinking about starting on the job this weekend, just paranoid. Also getting mixed local information on whether I can flush the condenser

2000B6S4, did you flush it yourself or take it to a shop? Looking at ac flush kit on amazon that uses compressed air

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**2004B6S4** · 09-30-2017 10:06 PM

ya, I flushed it myself with a flush gun I bought online. first I tried to rent one at the local parts store but it was a shitty type with a schrader valve instead of an air hose adapter, so then I returned it and bought one online. Using a professional A/C machine would be ideal for that but from what I read you should be ok as long as you have a decent air compressor powering your flush gun. Our car doesn't have the newer style of condenser you might hear about which is impossible to flush effectively, but it still has a lot of tubing running through it so you want to flush the hell out of it. pulsating the flow can help (the pro machines pulsate a lot faster than you can manually, but it'll still help). You can also get aftermarket filters to add to your a/c lines if you're worried about it, I didn't though. I've only driven about 8k miles since I did mine but so far so good.

**Dagear** · 10-01-2017 07:29 AM

Great thanks

I have a love hate relationship with this car. Hate all the things that break and the pain it is to replace but love driving it.

I plant to take condenser to import shop and have them flush it.

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**Velox** · 10-01-2017 08:22 AM

Hijack Question. CanI check if the compressor is still spinning/ shaft broken without removing the engine mount/brackets? having ac failure myself

**Dagear** · 10-01-2017 08:34 AM

Yes you c
Can easily see shaft from underneath

I also purchased a small USB camera from Amazon to help me inspect areas I cant see easily. Careful of rotating parts

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**Velox** · 10-01-2017 08:39 AM

Ok thanks

**Dagear** · 10-16-2017 06:27 PM

I have received all my parts.

New Compressor - Denso from Parts Geek
New Condenser
New AC O -ring kit
New Oriface.
Nitrogen tank to purge system with.

Overkill probably but my Air compressor generates lots of moisture. so Opted to rent Nitrogen tank to use while flushing lines. Using regulator from MIG Welder.

Questions.

1. I am concerned whether after flushing I need to add more lubricant to system. Sticker on compressor states it contains a full system charge of lubricant; however, buddy states each system is different and how could they make that statement. You guys that have completed an AC swap, what did you do for lubricant.

2. How paranoid do I have to be at moisture. Can I flush the lines, evaporator etc. over the course of a week? I realize flushing and reassembling within 1 day is ideal but not realistic for me.

3. Once it is assembled am I safe to drive the car to dealer to charge or do i risk the compressor seizing again?

**JayDog747** · 10-16-2017 08:23 PM

Will you be using a vacuum pump?

**2004B6S4** · 10-17-2017 03:56 AM

^^ I don't think a nitrogen purge is really necessary but I'm sure it won't hurt... what you need to do is evacuate (with vacuum) prior to recharge. If you're taking it to a shop for the recharge then they'll take care of that. Mine also came prefilled with oil and the only thing I added was pure r-134a. I don't think the same compressor is used for any other vehicle, so that makes it easy for the manufacturer to know how much oil to use.

As far as starting it up without filling the system, read this: https://drive.google.com/file/d/0B6G...ew?usp=sharing. The short answer is that it's not ideal but it can be done for a short distance because the compressor has an internal oil circuit to keep itself lubricated when the lines are empty.

**roboto_1337** · 10-17-2017 04:38 AM

Originally Posted by Dagear

I have received all my parts.

New Compressor - Denso from Parts Geek
New Condenser
New AC O -ring kit
New Oriface.
Nitrogen tank to purge system with.

Overkill probably but my Air compressor generates lots of moisture. so Opted to rent Nitrogen tank to use while flushing lines. Using regulator from MIG Welder.

Questions.

1. I am concerned whether after flushing I need to add more lubricant to system. Sticker on compressor states it contains a full system charge of lubricant; however, buddy states each system is different and how could they make that statement. You guys that have completed an AC swap, what did you do for lubricant.

2. How paranoid do I have to be at moisture. Can I flush the lines, evaporator etc. over the course of a week? I realize flushing and reassembling within 1 day is ideal but not realistic for me.

3. Once it is assembled am I safe to drive the car to dealer to charge or do i risk the compressor seizing again?

I blew my lines out with compressed air. Reassembled and took it to my Indy shop for recharge. My compressor came with oil but it didn’t seem like enough from what the Bentley said. My mechanic added oil during the recharge his exact words were “too much oil won’t hurt the system, if you don’t have enough you’ll wind up replacing the compressor again.”

Needless to say did a system evac, and vacuum test then had it recharged with r134a and compressor oil.

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**Dagear** · 10-17-2017 06:02 AM

Yes, I have a vacuum pump. I have held off working on AC systems for a long time, but took the plunge and assembled a vacuum pump, flushing equip, gauge set as I have 3 AC Systems to get working, S4, Buick Regal, Honda CRV. Another intended use is to make a vacuum can to use for power bleeding brakes, and other fluids.

2004B6S4, so you simply flushed the lines blew them out, assembled then added freon. I think I saw low and high side pressures on engine compartment sticker, I do remember seeing 500 gram of refrigerent. Also, so many opinions on condenser replacement or flush. The Oriface tube was pretty bad.

**Dagear** · 10-20-2017 07:05 PM

Well tonight I got the air-conditioner compressor installed engine mount was buttoning everything up and then realize that I had taken out the oil dipstick when I re,over the compressor so tomorrow I will take the air conditioner back off

Any tricks to mounting the shaft to the back of the compressor it feels like compressor is pretty well registered against the engine block but thought about leaving the mounting bolts of it loose as I tighten in the shaft up that way I know that it was in perfect near perfect position not to bind the shaft

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**BCsniper** · 10-20-2017 07:28 PM

Huh? I'm lost, why would you take the compressor back off??

Hook up the freon lines, put the diptstick tube, motor mount, and sway bar back on and you're done. I just now got my 4th AC compressor and will put it on tomorrow. There's not a lot to it, swap the compressor, put on a new drier and orifice tube. Then take it to be flushed and charged and you're done. That's pretty much it. If you can get the compressor off then you've done 75% of the job. Getting that bitch out of there is the hardest part. It's all downhill from there

**Dagear** · 10-20-2017 08:09 PM

I must be doing something wrong then because I can't get the oil dipstick tube in with the compressor mounted

That be great if I could do it that save me some work tomorrow

Need to ask why four compressors you have that many miles on your car

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**Dagear** · 10-23-2017 08:06 AM

First Notes for anyone else doing this job

1. Don't forget the alignment bushings, they may be left in your old compressor, look like ferreles from compression pipe fitting
2. Oil Dipstick tube is rotate 90 to remove, must be removed to install new compressor.
3. I removed thermostat to water pipe hose, but procedure may be able be accomplished with this hose installed

**Dagear** · 10-29-2017 12:35 PM

Got the system all back together and then was attempting to charge with small cans of r134a. I could only get low side to 50 psi could never get compressor to turn on

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**Velox** · 10-29-2017 04:27 PM

Originally Posted by Dagear

Got the system all back together and then was attempting to charge with small cans of r134a. I could only get low side to 50 psi could never get compressor to turn on

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Just finished A/C compressor replacement today. My Compressor also didnt turn on when charging empty system, econ light on/compressor stayed off but after restarting the engine econ light turned off and compressor turned on and I could resume charging.

If it still doesnt work you can check the reason why the compressor doesnt turn on with vcds:

go to hvac measuring block 2
The number in the first field is the compressor shut of code:

Breakdown of compressor shut-off conditions
0 Compressor on (no shut-off condition detected.)
1 Compressor off (pressure in refrigerant circuit was or is too high.)
2 Compressoroff (basic setting not performed or not performed without error.)
3 Compressor off (pressure in refrigerant circuit is too low.)
4 Compressor off (engine nor running or has been running for less than 2 sec.)
5 Compressor off (engine speed is below 300/ min.)
6 Compressor off (compressor switched off by ECON118°C.)

12 Compressor off (request from the engine control unit, via data bus.)

13 Compressor off (faulty signal from refrigerant pressure and temperature sender
-G395.)
14 Compressor off (fault in data bus system.)
15 Compressor off (the pressure in the refrigerant circuit in this driving period was at least 30 times too
high.)
16 Compressor off (the measured temperature downstream of the evaporator has for over a minute been below
0°C.)
17 Compressor off (measured temperature downstream of evaporator below -5°C.)
18 Compressor off (there is no valid measured value for theambient temperature, possibly both
ambient temperature sensors -G17 and fresh air blower intake duct -G89 defective.)
19 Compressor off (-Climatronic control unit -J255
was switched on via the "auxiliary heater" function.)
20 Compressor off (readout currently vacant)
21 Compressor off (measured ambient temperature wasbelow -8°C and is still below
-5°C, there is no request for automatic recirculated air mode or the measuredambient temperature
was below +2°C and is still below +5°Cand the "automatic recirculated air mode" function is not
active.)
22 Compressor off (measured passenger compartment temperature below +8°C. The measured
ambient temperaturewas below -8°C and isstill below -5°C. Arequest for
recirculated air mode has been received.)
23 Compressor off (via the data bus system a fault message for activation of the
radiator fans was sent, e.g. by therelevant engine control unit,and received bythe
Climatronic control unit -J255.)
24 Compressor off (readout currently not used.)
25 Compressor off (readout currently not used.)

**Dagear** · 10-31-2017 10:22 AM

Should I have any concerns with driving the car to a shop with small amount of Freon in the system? Should I evacuate the system again?

**roboto_1337** · 10-31-2017 10:32 AM

Originally Posted by Dagear

Should I have any concerns with driving the car to a shop with small amount of Freon in the system? Should I evacuate the system again?

The issue would be that Freon in your system may contaminate the R134a in the shops HVAC equipment. I would evac again and let them know that you previously had it charged with R-12.

**Dagear** · 10-31-2017 10:36 AM

My bad had r134a not freon or r12

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**mrh12000** · 10-31-2017 02:40 PM

On mine, the AC quit and I thought it was the compressor, replaced and recharged etc and still did not work. It was tedious pain to do but not really that hard.
Took it to the indy mechanic and he pulled the compressor drive shaft and said that the drive hub was shot (there was some wear on the drive shaft splines but not so much as to think the issue is the shaft). What he said was the rubber seal between the shaft and the engine case can gook up so badly as to create enough drag to cause the hub to fail, and that he likes to clean and lube that seal to prevent that from happening.
So I understand the fix (and he did not try and get me to do it) is to pull the engine and replace the drive hub, and as I have 100k miles, replace the tensioners etc. I have not been able to get a look at what the hub is supposed to look like. I assume its just one of the cogs in the gear set. Anyone have a picture?
On a related side note, I have a line on a low mileage S5 4.2 engine, I dont want to try to swap the whole thing as it is complex, I don't know if the short block would be same to swap that (along with chains etc), any thoughts?

**BCsniper** · 10-31-2017 02:51 PM

I actually have the same issue. However I am hoping most of my damage is to the shaft and not the drive unit. I posted pictures in the "What you did to your S4 today" thread of what my current shaft looks like vs a good one. If you want to replace that drive unit, it will be a motor out job and if you haven't done timing then it's a perfect time to. I did mine a couple years ago so I am VERY reluctant to pull the motor again for an A/C system.

Here is a picture of the back of the motor. Look at the 3 sprockets together in the bottom left corner. It's the one on top of those 3, where the Audi logo is stamped. This is the back side of it

**mrh12000** · 11-01-2017 12:12 AM

My shaft spline is not as bad as yours so maybe mine is the drive sprocket, rats
Did you do chains or tensioners (or both), I don't have start up rattle.
It does look beautiful, do bad so fragile.
Thanks
Going to be a heck of a job for a rotten little problem.
Not sure how they call up that sprocket

**mrh12000** · 11-01-2017 12:18 AM

I don't know if it's wishful thinking that I could swap the S4 short block for an S5...

**BCsniper** · 11-01-2017 03:53 AM

The S5 motor is not the same as the 4.2 in the S4. Honestly no other motor is besides the one they put in the Allroad for 1-2 ywars. The S5 motor is very much like the RS4 motor. It's almost the exact same as the RS4 except without beefed up internals. For the FSI 4.2 motor there was the high-revving performance version (RS4) and the "comfort" version seen in the Q7/A8. The S5 is kind of in the middle of the two. It does not have the forged bottom end that's found in the RS.

I'd suggest getting JHM's intermediate kit (or just piece all the same parts together from elsewhere if you'd like). New tensioners, guides, and cam sprockets should make your motor last another 100-150k miles so long as it's maintained and doesn't start eating oil like it's going out of style.

**mrh12000** · 11-01-2017 07:57 AM

Thanks for you continued support on this thread.
I understand that the S5 uses the FSI system of direct injection versus port type injection, but that is all in the heads and intake (and harness, computer, fuel injection) etc, could the short blocks be the same though?