JMB RetrofitsAH Fabrications
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  1. #1
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    Compressor failed?

    Hi guys... the other day I stopped getting cold air from my air con. Scanned the HVAC unit for codes with VCDS and it's clean. It will happily claim to switch into and out of ECON mode but the clutch on the compressor does not engage at all, I have watched under the bonnet whilst having someone press the ECON button on and off, and it doesn't engage at all. I used the Climatronic diagnostics stuff and all the time the voltage for the AC Compressor (Code 20) is 14v and the high-pressure switch status is always 1.

    So my questions are...

    High pressure switch at 1 - is that good or bad?
    AC compressor code 20 at 14v - does that mean it's on or off?

    Has my compressor clutch failed, as it doesn't seem to try and engage even with 14v, or would it normally engage at 0v?

    Just trying to diagnose it a bit myself, because I know that if I take it to any garage around here their first step will be to re-gas the system and charge me lots for it!

    Thanks in advance!

    Steve

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  3. #2
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    So... an update. I wired my compressor direct on the battery in order to test it and it successfully engaged.

    Tried this with the engine running and I got air con for about 2 minutes... then *pffffffffffft*! A big cloud of rather odd smelling fumes (refrigerant, I assume) out from under the bonnet.

    Took it down to a local Kwik-Fit and they regassed it for me, but the compressor still won't engage. They didn't charge me for it, as they couldn't get it working :-)

    I'm assuming the a/c controller is not switching on the compressor for some reason (presumably to prevent what happened to me!) and I need to find the other fault and rectify it. Any ideas what else the controller would check before allowing the system to start?

    Steve

  4. #3
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    So... having re-read the FAQ again, I've got to the conclusion that the condensor fan not starting may be my problem. I got home after my usual commute and neither of my fans were turning at all, but there was a high pitched noise coming from the back of the fans... all the fuses are fine... so perhaps the fan controller. Hopefully my little monologue will be useful to someone in the future, so I'll continue!

  5. #4
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    Used VCDS to read block 1 of the HVAC Controller. I got a code of 0. Based on the labels below, that means the AC unit thinks that the compressor should be running!

    Haynes wiring diagram shows that the compressor clutch is fed directly from the Radiator Fan Control Unit... perhaps I need to find out what readings I can measure from that or look into replacing it.

    Codes:

    001,1,Comprossor,Shut-Off,Specification: 0 = Compressor Running
    ; 0 = Compressor Running
    ; 1 = Compressor OFF by Pressure Switch (F129): Refrigerant Pressure too High
    ; 2 = Compressor OFF by Fresh Air Blower (V2) or Fresh Air Blower Control Module (J126) Malfunction
    ; 3 = Compressor OFF by Pressure Switch (F129): Refrigerant Pressure too Low
    ; 5 = Compressor OFF by Missing Engine Speed Signal
    ; 6 = Compressor OFF by ECON Button
    ; 7 = Compressor OFF by OFF Button (via Fresh Air Blower Speed Buttons)
    ; 8 = Compressor OFF by Ambient Temperature below 3 °C (37 °F)
    ; 10 = Compressor OFF by Voltage below 9.5 V
    ; 11 = Compressor OFF by Coolant Temperature too High
    ; 12 = Compressor OFF by Engine OR Transmission Control Module
    ; 13 = Compressor OFF by Voltage above 17 V
    ; 14 = Compressor OFF by Evaporator Temperature
    ; 15 = Compressor OFF by Control Module Coding incorrect
    ; 16 = Compressor OFF by Climate Control Module (J255) Malfunction
    ; 17 = Compressor OFF by Pressure Sensor Malfunction
    001,2,Engine Speed,recognized,Display Range: 0 = no/1 = yes
    001,3,Vehicle Speed,,Display Range: 0...255 km/h
    001,4,Standing Time,,Specification: 0...240 Min | 250 = Battery disconnected | 255 = Transfer Malfunction

  6. #5
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    I think i have the same problem as you, but my technical understanding ran out after the 1st post, when you sort it, let us know how.
    2001 AMK ...Black

  7. #6
    Staz's Avatar
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    So basically you broke your own air con system by being silly and bypassing all the safety cut-outs. Did the compressor still run after you blew a leak into the system?
    8P2 S3

    For advice on Air Con problems please read my FAQs.
    To find ASN members with VCDS check out the MAP.

  8. #7
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    Basically, yes... Pretty stupid, I know. The compressor clutch is still capable of engaging, but it still doesn't do so automatically. Do you have any recommendations as to what I should check next? You know a lot more about air con than me, so if you've got any helpful hints, that would be great.

  9. #8
    Staz's Avatar
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    Well you've blown a leak in the system somewhere so that's the first thing you need to find and fix it. After that, your diagnostics method for the original fault was understandable and at least you have isolated that the compressor clutch works. It's reasonable to assume that the system is trying to send the signal to the compressor but it's not getting there, unfortunately it may not be that simple.

    It may be as simple as a faulty relay, but I don't know.
    8P2 S3

    For advice on Air Con problems please read my FAQs.
    To find ASN members with VCDS check out the MAP.

  10. #9
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    Is there a safety pressure blow-off valve in the system anywhere? When I had it regassed yesterday, it passed the leak test successfully... which suggests the venting was controlled and it's no longer leaking.

    I've got hold of a diagnostics process for the Radiator Fan Control Unit (which takes input from the HVAC controller and is responsible for operating the fans and the compressor) so I'm hoping to go through that (involves multimetering different contacts) and see where that takes me.

    Is it feasible that within the two minutes I forcibly ran the a/c for, the lack of a fan on the condensor would cause the system pressure to get high enough to blow a leak/blow a safety valve? Or does it indicate a deeper problem?

    If it's just the fan, the contol unit might not switch the compressor on unless the fan is running (i.e. faulty fans/wiring)? Or the control unit has failed and therefore no compressor or fans, perhaps?

    Steve

  11. #10
    Staz's Avatar
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    Is there a safety pressure blow-off valve in the system anywhere? When I had it regassed yesterday, it passed the leak test successfully... which suggests the venting was controlled and it's no longer leaking.
    Nope there are no blow off valves as it would mean that refrigerant is vented to atmosphere which no one wants as it's a greenhouse gas. A leak test is almost pointless if the system is not running as that's when the pressures rise to levels that would show a leak.

    I've got hold of a diagnostics process for the Radiator Fan Control Unit (which takes input from the HVAC controller and is responsible for operating the fans and the compressor) so I'm hoping to go through that (involves multimetering different contacts) and see where that takes me.
    Hopefully that'll find something!

    Is it feasible that within the two minutes I forcibly ran the a/c for, the lack of a fan on the condensor would cause the system pressure to get high enough to blow a leak/blow a safety valve? Or does it indicate a deeper problem?
    I know that if you run a system without a condenser fan running it doesn't take long until the high pressure cut-out trips, it's been a few years but two minutes sounds about right. How long it takes before a leak I really couldn't guess. I would hope that a HPCO comes in a long time before any damage could be done. Also if the HPCO was faulty the system would still cut off due to the low pressure cut-off, this normally takes a bit longer to kick in though IIRC, this suggests to me that two minutes shouldn't be long enough for damage to be caused.

    If it's just the fan, the contol unit might not switch the compressor on unless the fan is running (i.e. faulty fans/wiring)? Or the control unit has failed and therefore no compressor or fans, perhaps?
    That could be a fair conclusion as your Haynes says the signal comes from the radiator control unit. I would have hoped there'd be a couple of fault codes generated though! What car is this on BTW?
    8P2 S3

    For advice on Air Con problems please read my FAQs.
    To find ASN members with VCDS check out the MAP.

  12. #11
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    Ah yes, never actually mentioned... this is an 8L S3, Facelift 2001. Having followed the diagnostics on the RFCU, it got to the point where I was testing the connectors with the engine running and it said to check between A5 and A6 and to expect battery voltage... 0v - it suggests using wiring diagrams to check for a short on the link between the A/C controller and the RFCU. but my Haynes manual says that A5 is jumpered to A14... so if the connector is off, that means it won't show anything - not sure whether the Haynes is accurate.. it's not jumpered right on the connector.

    Not relishing the prospect of trying to diagnose a short in the link between the two units through the bulkhead... going to try and find a better wiring diagram. Hoping for a relay, fuse or other simple problem in there somewhere!

  13. #12
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    Have checked a VAG wiring diagram and pins 5 and 14 are indeed connected together, meaning I was testing between a bit of bare wire and a negative, which wasn't a very good test. Unfortunately away at the weekend, so when I return I'll resume the rest of that diagnostics procedure.

    I did read a thread somewhere suggesting that the low-speed resistor in the standard VW radiator fan has a habit of failing... I may try and wire the fan straight off the battery tomorrow lunchtime and see if I can make it run at both slow and full speeds. Although I'm not sure if that would stop the AC working...

    Edit: Turns out that reaching the fan connector is not very easy... not a lunchtime job unfortunately! Also confirmed there is a leak on the system now, there's residue around that looks to have originated from the join between the compressor and one of it's pipes.

    Steve
    Last edited by stevehaskew; 4th June 2010 at 12:59.

  14. #13
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    Quick update... It's miraculously started working... I have no idea why!

  15. #14
    Staz's Avatar
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    Re: Compressor failed?

    And not leaking??
    8P2 S3

    For advice on Air Con problems please read my FAQs.
    To find ASN members with VCDS check out the MAP.

  16. #15
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    Ok, so after I attempted to fiddle with the fan connectors at work on Friday, the a/c worked for the whole of my Friday evening drive to Cardiff.. when I got in the next morning, it was broken again. That's kind of expected, as Staz hinted at above, it's leaking. The difference now is that although it doesn't blow cold air, it does try to engage the compressor, but then it clicks back off very quickly. I'll stick VCDS on it at lunchtime and I'm expecting to see block 1 showing a code of 3 - Refrigerant Pressure too Low.

    So I know that the leak is between the compressor and the hose out from there.. not sure whether it's on the metal pipe that attached to the compressor or whether it's where the metal pipe meets flexible hose. Should it be a very simple job to fix? *If* the system is completely empty already, is the fix something I could attempt myself, then get it refilled?

  17. #16
    Staz's Avatar
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    If you're any good with brazing maybe. Or you could replace the whole section. Not sure to be honest.
    8P2 S3

    For advice on Air Con problems please read my FAQs.
    To find ASN members with VCDS check out the MAP.

  18. #17
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    Will take a look. Interestingly I just looked at the diagrams and there is actually a pressure relief valve on the compressor, so I think my original venting was probably through that... although it still remains that I have a leak of some kind somewhere! Will let you know what I find.

  19. #18
    Staz's Avatar
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    Hmm okay then, I'll remember that one!
    8P2 S3

    For advice on Air Con problems please read my FAQs.
    To find ASN members with VCDS check out the MAP.

  20. #19
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    So... haven't had much time to work on the car in the last week, but managed to get time tonight. Since last week and the miraculous recovery of the a/c, it has once again started suffering the electrical problem of the HVAC controller believing the compressor is running. So I've gone back to where I left off with the diagnostics. As it stands now, neither rad fan will run at any time. I disconnected one of the radiator fans and ran it off the battery, and it would run at both low and fast speeds. I didn't actually manage to reach the other one. So I've decided to replace the Radiator Fan Control Unit, which is the box that does the actuation of both fans and also the compressor. Will try and get hold of one tomorrow, hopefully. I'll report back how I get on.

    Steve

  21. #20
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    Picked up two RFC units from the local scrapyard for Ł20 the pair - much better than the Ł108 before VAT that Audi quoted me! Only problem is that these units may be faulty too... hopefully not.

    Also took a closer look at the pressure relief valve. The manual I've read says that it opens when the pressure exceeds 38 bar and closes again when the pressure drops below 30 bar. Mine has definitely opened at some point, the sticker over the end is flapping around.
    Last edited by stevehaskew; 18th June 2010 at 01:02.

  22. #21
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    Right... time for another update. I'm hoping this is useful to someone in the future, so I'll keep on posting until I resolve the problem, even though I'm not asking any questions as such.

    So, replaced the Radiator Fan Control Unit (J293) and there is no change at all :-(

    I got a local a/c specialist to come out and have a look, and he checked pressures. With the system not running, the high pressure side is at 6 bar, when it should be at around 2 bar. The guy said this is almost certainly a blockage in the expansion valve, so that will need replacing. Also, it is quite possible that the reason the valve is blocked is due to swarf from a failing compressor. So, it looks like I have two problems here, one being the cause of the other.

    1. My radiator fans are not running, which causes both the engine and the a/c system to overheat.
    2. My a/c expansion valve is blocked and needs replacing, probably along with the compressor.

    I've re-investigated the diagnostics procedure for the RFCU and it looks like I used the wrong process. I need to run through the new one, and because I have map-controlled cooling, that will involve getting a registered version of VCDS in order to do test actuations of all the different components.

  23. #22
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    Latest update is that I had a local VAG specialist take a look. They identified that although the fuses on the battery had not blown, the contact at one end has got hot and melted plastic in the vicinity. They cleaned up the contacts. They also swapped my J293 again, for the other of the ones I got from the scrappy the other week. The rad fans now run when the car is too hot, and will run on after the car stops when necessary.

    Also, and I think most significantly, using VCDS to measure the block for the compressor, I now get a reading of 3 - refrigerant pressure too low, which is exactly what I'm expecting, as the A/C specialist left the system empty for me so that I could safely replace components myself, before returning it to him to have it recharged.

    Hopefully the end is now in sight!

  24. #23
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    So, finally... I have working (for now) air con. Don't know how long it will last! Here's a summary of the fix:

    Fuse socket on top of the battery had bad contacts, meaning problems with the Radiator Fan Control Unit. Repairing the contacts and replacing the control unit has resolved the electrical problems.
    Expansion Valve blocked - fairly trivial to replace *if* somebody has emptied your system for you.

    Services:
    Air con Diagnostics - Ł25
    Electrical Diagnostics - Ł70
    Re-gas - Ł49

    Parts (from scrap yard):
    Fan Control Unit - Ł10
    Expansion valve - Ł10

    Total cost: Ł164

    The total cost is actually more than that, because I've ended up with parts I haven't used.

    My advice to anyone with the same problem is that if you're fairly mechanically minded, you can fix this yourself, with the right help for some of the tasks. If you're trying to do it cheaply, do as much as you can yourself.
    When I first started this, I was scared of working on air-con and thought that only professionals could do it. That's not completely untrue; When it comes to the gas, leave it to the pros. For the rest, take a look at it before you hand it (and lots of money) over to somebody else.

    Steve

 

 

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