Audi A6 Quattro 4.2 V8 Air conditioning reality check request, and some questions
04-30-2017, 12:38 AM
#1
AudiWorld Member
Thread Starter
Audi A6 Quattro 4.2 V8 Air conditioning reality check request, and some questions
I bought the license to the electronic version of the Bentley manual for the A6, and I’ve worked through the information relevant to air conditioning, as much as I could stand. Good stuff, to be sure, but it doesn’t exactly make for easy reading by my standards, and I still have questions. I have also (not recently, but … still) worked through the EPA subject matter for becoming certified as an automotive air conditioning tech, even though I haven’t taken the test yet. So, I have at least a clue, and I’m asking for for help only after doing some due diligence first.
The principles make sense to me but I don't know how some of them are applied in the context of my 2000 Audi A6 4.2 V8 cars. I have two operational ones, a black one whose air conditioning works well, and a silver one whose air conditioning doesn’t blow air colder than ambient, which I conclude based on sticking a thermometer into the vents. The black car blows out air at 40 F or so; the silver car blows out air at 80 F or so, around noon on a spring day in Nevada.
I rented the Autozone gauges and hooked them up to each car. The black car’s low side reading varies but it’s near 40 psi or so much of the time. With the air conditioning on (engine at operating temperature, controls to max cold) the high side pressure reading varies but it’s near 220 psi or so much of the time, low side. So that’s on the black car whose air conditioning works well by my standards.
On the silver car, whose air conditioning doesn’t work, the low side reading is just under 40 psi much of the time. I read somewhere (Bentley, as I recall) that the low switch compressor cut-out occurs at 25 psi, so we’re safely above that. With the air conditioning on (engine at operating temperature, controls to max cold) I can hear a click as the compressor clutch kicks on. Before I turned the controls on, a friend of mine, who doesn’t mind getting dirty, was lying on the floor looking up at the compressor. The pulley was being turned by the belt attached to the engine; the inside mechanism of the compressor was not. Then, I turned the control on and my friend saw the inside mechanism of the compressor energize and turn at the same speed as the pulley.
As I understand things, this means that all the reasons that can make a compressor not turn on when I want it to (low refrigerant pressure, bad pressure switch, bad wiring, bad controls) can all be ruled out. The compressor is turning. Problem is, it’s making no difference. Whether the compressor was on or off, the high side reading remained at 60 psi. So, it seems to me that I need a replacement compressor. I have six of them in used condition so that’s okay with me. I have an appointment at a local shop in Reno who might or might not be open to installing a used part at my risk. Also, they’re certified to deal with the refrigerant management issues and I’m not, even though I have an evac machine, so I’ll let them deal with it. At least I’ll be an informed customer, assuming I’m making sense.
So, question 1: Am I making sense?
But, there’s more. What puzzles me is the concept of moisture in the lines. As I understand things, moisture in the lines is a very bad thing. In the context of a BMW E30 3-series (my comfort zone) there’s something called a receiver-drier. If you take that part out of the car and leave it outside for a while, it’s ruined due to moisture from the outside air having gotten into it. So, when installing a replacement, it has to be out-of-the-box new, and it had better be left sealed until it’s installed.
I don’t recall seeing a receiver-drier in the Audi material I read nor do I remember seeing one while working on any of my C5 Audi A6 cars (perhaps because I don’t know what it looks like or where it is). So my questions on this subject are:
- Is there such a moisture-removing part in the context of a 2000 Audi A6 Quattro 4.2 V8?
- What is it called?
- Where is it located?
- How does it work so as to remove the moisture from the lines?
- What does it do with the moisture it removes?
- Is it possible for this part to remove too much moisture, i.e., does it aim for a certain level of humidity?
- How long does it live when properly installed?
- How long does it live when its insides are exposed to the outside air?
- How can I test it?
- How can I test the humidity of the refrigerant in the lines?
On a related subject, the lines need to be filled with not just R134a but also oil (PAG, not mineral oil as was used for R12). Questions:
- Is there a way to test the oil content of the refrigerant in the lines?
- What’s the optimal value?
Perhaps all of this is also in the Bentley but my eyes glaze over when I look at its air conditioning section any more than I already have, so please help.
Thank you!
~Tanya
Last edited by tanya_charbury; 04-30-2017 at 12:41 AM.
04-30-2017, 08:51 AM
#2
Receiver Driver is metal cylinder under right headlight. Lives forever unless opened to air for more than a few minutes. I don't think the receiver dryer is your problem.
I think the only way to insure proper oil quantity is to evacuate and refill to spec. Unless your system has been messed with and/or has a big leak, oil should be OK.
I haven't had to troubleshoot my A6 AC system, so I don't know all the possible relays and switches that could cause the problem. I wonder if you have a door flap that isn't directing the cold air to the outlets.
I just had the dealer recharge the AC on my 4.2 touareg after being unable to get it to take 134a from a can. They had problems also and had to evacuate twice before it would accept a charge. They put dye in so we can find the leak when the AC dies again.
I rebuilt the AC on a Saab 900 and once is enough. I put new receiver dryer in when I did the Saab hoses, but I'm not sure it was necessary.
I think the only way to insure proper oil quantity is to evacuate and refill to spec. Unless your system has been messed with and/or has a big leak, oil should be OK.
I haven't had to troubleshoot my A6 AC system, so I don't know all the possible relays and switches that could cause the problem. I wonder if you have a door flap that isn't directing the cold air to the outlets.
I just had the dealer recharge the AC on my 4.2 touareg after being unable to get it to take 134a from a can. They had problems also and had to evacuate twice before it would accept a charge. They put dye in so we can find the leak when the AC dies again.
I rebuilt the AC on a Saab 900 and once is enough. I put new receiver dryer in when I did the Saab hoses, but I'm not sure it was necessary.
04-30-2017, 09:42 AM
#3
AudiWorld Member
Thread Starter
This is very helpful. Thank you!
I see your point ... perhaps cold air might be "created" but might not be finding its way out the vents.
Is my reasoning valid that the compressor is likely the issue?
If yes, I guess I don't really see much point in paying someone $50 just to have a disagreement on whether or not to use the compressor I furnish.
Your Touareg experience makes me nervous. As to your Saab experience, I feel the same way about BMW air conditioning.
Thank you again!
I see your point ... perhaps cold air might be "created" but might not be finding its way out the vents.
Is my reasoning valid that the compressor is likely the issue?
If yes, I guess I don't really see much point in paying someone $50 just to have a disagreement on whether or not to use the compressor I furnish.
Your Touareg experience makes me nervous. As to your Saab experience, I feel the same way about BMW air conditioning.
Thank you again!
04-30-2017, 02:41 PM
#4
When I scanned the touareg with VCDS, I did get a low refrigerant code. When I hooked up the can of 134a, there was a spritz at the connector indicating not empty.
Not sure if the v8 has the same fans, but when my AC is on, 2 fans kick in.
Maybe try cycling the HVAC controls through all settings a few times to see if a flap might free up.
Not sure if the v8 has the same fans, but when my AC is on, 2 fans kick in.
Maybe try cycling the HVAC controls through all settings a few times to see if a flap might free up.
04-30-2017, 03:57 PM
#5
AudiWorld Senior Member
I'm not certified on a/c either but had two mechanics working for me that were. In my opinion if the oil was the issue the compressor would seize in short order. Since that hasn't happened, then it is probably okay. When charging the system at a pro shop they are going to hook up the machine and evacuate the system of all refrigerant. They have a recovery tank on the machine to contain the old gas. Then my guys, after putting the system into a negative pressure condition (vacuum) would leave things hooked up and shut down their machine for about an hour. If the system lost vacuum pressure then there is a leak somewhere in the system. If not then it was okay to recharge the system with the correct amount of refrigerant.
Although not certain, it sounds like johnkk is on the right track. Sounds like an air flow diverter flap isn't moving into position like it should.
Although not certain, it sounds like johnkk is on the right track. Sounds like an air flow diverter flap isn't moving into position like it should.
05-01-2017, 04:24 AM
#7
Yes receiver dryer is the accumulator.
One other thought, while most compressors have an on/off clutch, Bentley lists another. It's regulator controlled and I have a hunch that's what's in 4.2's. I believe that these compressors spin all the time, but may only pump refrigerant when the regulator kicks in. If that's the case, your spinning compressor may not be pumping due to low refrigerant or a regulator activation problem.
I think you might consider an A/C pro who has 4.2 system experience. I would run a VCDS scan if you haven't.
One other thought, while most compressors have an on/off clutch, Bentley lists another. It's regulator controlled and I have a hunch that's what's in 4.2's. I believe that these compressors spin all the time, but may only pump refrigerant when the regulator kicks in. If that's the case, your spinning compressor may not be pumping due to low refrigerant or a regulator activation problem.
I think you might consider an A/C pro who has 4.2 system experience. I would run a VCDS scan if you haven't.
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05-05-2017, 07:06 PM
#8
AudiWorld Member
Thread Starter
It's Friday evening, and I'm feeling chatty so the signal-to-noise ratio is bad on this post, sorry.
I ran the VCDS scan, and it claimed all was well. My friend checked the compressor on a healthy car (my black one). With the engine running, the pulley always spins but the inside part spins only when the A/C kicks in. Probably a more precise way would be to say "when the A/C compressor clutch engages."
In Reno, there's one "go to" place that the not-A/C-savvy mechanics hereabouts recommend for A/C work. I went there fifteen years ago for my 1988 BMW 750iL. They diagnosed that it needed a new compressor and just that part alone was going to be $500. I said "no" and after that, I drove it with the sunroof and windows open like when I was growing up as a little blonde girl in South Africa. We didn't have A/C but I turned out just fine. When it gets to be too much to handle (Nevada desert summers) I simply empty a bottle of water over my head and that cools me right off. I do get funny looks from the civilized people, though. The car blew its fuel pump a few years ago, so its A/C problem is automatically solved since it's been dead ever since.
Back to 2017. I made an appointment, and did the drop-off the afternoon before. I brought along two used compressors and a detailed letter explaining that I buy entire cars for $500 including typically good compressors so I wasn't planning to spend $500 on a new unit, yet I was happy to pay them to bench-test the two used units and I would happily assume all the risk and liability on the whole transaction. The front desk lady read my letter and said it made perfect sense.
I got a call the next morning, announcing the news.
Yes, they confirmed, the compressor is bad.
No, they don't have a test bench.
No, they won't use any parts I supply.
Estimate for the fix: $1,235.
I paid $1,200 for the entire running, driving car so I'm not keen on spending $1,235 on a new compressor and install.
The experience really helps me relate to why the resale parts of these delightful cars is so low. Getting them fixed is intimidating due to high prices. That's how I got into the used parts business in the first place -- I could either complain about the prices for parts for my 1980s BMWs or I could remember what I learned in college about economics. Prices depend on supply and demand. So with me now being in the parts business, the prices are lower because I add to the supply, and I don't buy stuff from normal vendors so the demand is lower, so yay for the invisible hand of the market. I'm not making any money yet but I feel empowered. I don't have to be mean to parts guys when they tell me high prices; I just go to plan B.
Plan B in this case meant that I poked around on the Web and found an 2004 article on bench-testing, by someone who's clearly savvy, and I hunted him down (nicely) and sent him a friendly email. He's a fountain of insight and he guided me as to navigate the maze of confusion and buy a new compressor affordably (less than $250). I've just ordered one. He's very much against cheap knock-off crap from China so I'm pretty confident I'm getting the real thing. The part numbers and the visuals check out.
So, next are the questions of:
- Does it come pre-oiled with PAG?
- Where do I go to install it?
... or do I become an EPA-certified A/C tech and do it myself? I already have most of the shop equipment but I have many irons in the fire already, and I don't wanna mess things up by being clueless nor end up with the EPA after me because I messed something up and killed all the polar bears by leaking refrigerant.
I ran the VCDS scan, and it claimed all was well. My friend checked the compressor on a healthy car (my black one). With the engine running, the pulley always spins but the inside part spins only when the A/C kicks in. Probably a more precise way would be to say "when the A/C compressor clutch engages."
In Reno, there's one "go to" place that the not-A/C-savvy mechanics hereabouts recommend for A/C work. I went there fifteen years ago for my 1988 BMW 750iL. They diagnosed that it needed a new compressor and just that part alone was going to be $500. I said "no" and after that, I drove it with the sunroof and windows open like when I was growing up as a little blonde girl in South Africa. We didn't have A/C but I turned out just fine. When it gets to be too much to handle (Nevada desert summers) I simply empty a bottle of water over my head and that cools me right off. I do get funny looks from the civilized people, though. The car blew its fuel pump a few years ago, so its A/C problem is automatically solved since it's been dead ever since.
Back to 2017. I made an appointment, and did the drop-off the afternoon before. I brought along two used compressors and a detailed letter explaining that I buy entire cars for $500 including typically good compressors so I wasn't planning to spend $500 on a new unit, yet I was happy to pay them to bench-test the two used units and I would happily assume all the risk and liability on the whole transaction. The front desk lady read my letter and said it made perfect sense.
I got a call the next morning, announcing the news.
Yes, they confirmed, the compressor is bad.
No, they don't have a test bench.
No, they won't use any parts I supply.
Estimate for the fix: $1,235.
I paid $1,200 for the entire running, driving car so I'm not keen on spending $1,235 on a new compressor and install.
The experience really helps me relate to why the resale parts of these delightful cars is so low. Getting them fixed is intimidating due to high prices. That's how I got into the used parts business in the first place -- I could either complain about the prices for parts for my 1980s BMWs or I could remember what I learned in college about economics. Prices depend on supply and demand. So with me now being in the parts business, the prices are lower because I add to the supply, and I don't buy stuff from normal vendors so the demand is lower, so yay for the invisible hand of the market. I'm not making any money yet but I feel empowered. I don't have to be mean to parts guys when they tell me high prices; I just go to plan B.
Plan B in this case meant that I poked around on the Web and found an 2004 article on bench-testing, by someone who's clearly savvy, and I hunted him down (nicely) and sent him a friendly email. He's a fountain of insight and he guided me as to navigate the maze of confusion and buy a new compressor affordably (less than $250). I've just ordered one. He's very much against cheap knock-off crap from China so I'm pretty confident I'm getting the real thing. The part numbers and the visuals check out.
So, next are the questions of:
- Does it come pre-oiled with PAG?
- Where do I go to install it?
... or do I become an EPA-certified A/C tech and do it myself? I already have most of the shop equipment but I have many irons in the fire already, and I don't wanna mess things up by being clueless nor end up with the EPA after me because I messed something up and killed all the polar bears by leaking refrigerant.
05-06-2017, 03:58 AM
#9
The manual says that new compressors are pre-filled with oil, but I would try to check. I would remove one of the plugs where the lines connect and tip the compressor. If oil drips out, assume it's filled. If dry add oil, or have it done when the system is filled.
Auto parts stores sell 134a cans with oil included, but how to evacuate without a machine. I personally would put the compressor in and have it evacuated and filled by a shop. I just paid $145 at dealer for this on touareg 4.2.
I wish I knew how the regulator controlled compressors worked. Re certification, many years ago, I considered this to be able to buy r-12 refrigerant. I read a book on it and the test prep online info, but never got the certification, because the machine was too expensive. Only if you're going to do this often and are going to buy the vacuum/capture/refill machine, would I get certified
Auto parts stores sell 134a cans with oil included, but how to evacuate without a machine. I personally would put the compressor in and have it evacuated and filled by a shop. I just paid $145 at dealer for this on touareg 4.2.
I wish I knew how the regulator controlled compressors worked. Re certification, many years ago, I considered this to be able to buy r-12 refrigerant. I read a book on it and the test prep online info, but never got the certification, because the machine was too expensive. Only if you're going to do this often and are going to buy the vacuum/capture/refill machine, would I get certified
05-06-2017, 10:16 AM
#10
AudiWorld Senior Member
johnkk is right on point. An a/c machine is not cheap be any means. You would be dollars ahead to continue your idea of finding serviceable used compressors and installing them yourself. You can most likely find a shop or technician that can do the testing/recharge at a favorable fee. If they get enough of your business, the more likely they are to cut you a bit of a break on pricing. If you have business cards and someone asks about a/c service refer them to the tech you are using and tell them to present your card when they get an appointment.