A/C Repair Tip
08-18-2017, 12:40 PM
#1
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A/C Repair Tip
Hi All,
Recently the A/C on my Q5 stopped working and I spent a half of a day troubleshooting it and scratching my head. In the end it was a simple fix but along the way I discovered that a lot of Audis have a common failure mode for A/C. Also, there was a lot of questions I had to dig into so I figured I would post my findings in the hopes it would help out others.
First, let me say that if you find this post because your A/C stopped working and you don't own a VAGCOM, then you should really get a VAGCOM. Assuming you are trying to do your own A/C repairs, you likely also do other repairs for which one of these is indispensable. I have no connection to the company, just a happy customer.
Second, assuming you have a VAGCOM, if your failure is like mine it is pretty easy to fix and you don't necessarily need a lot of specialized A/C repair tools.
Third, there is a TSB out that covers the symptoms - its number is 2020124 and is on the 'net several places. But I encourage you to find the most recent copy since it has been updated 13 times (as of today) to add more info. I have an Alldatadiy subscription and it is on there.
OK - here goes...
So the A/C just stopped working - blew hot air, compressor did not appear to be running.
First thing I did was pull out the VAGCOM and pull the codes and discovered the following:
00256 - A/C Pressure/Temperature Sensor (G395)
008 - Implausible Signal
This is where you need to get the TSB and follow its suggestions because if the 00256 code appears in concert with a 01592 code, the problem is most likely a cut wire that is common to the G395 sensor and a G238 sensor. I can't speak to how hard it is to chase down this broken wire since I did not have to do it. But I am sure it is fun...
The TSB also mentions that older versions of the G395 sensor were prone to leaking refrigerant. The G395 sensor on my Q5 is between the grill and the evaporator core on the driver's side. Since it was bone dry, I doubted it was leaking - refrigerant leaks almost always cause an oily spot where it leaks and mine had no oil at all on it anywhere. If yours appears to have oil on it, it has likely leaked down and not only requires replacement but also recharging of the system. This definitely requires a lot of special tools to do right so this would be a good time to seek professional help...
I did not have the 01592 code so I did not suspect the wiring was at fault. And since it was dry, I did not suspect a leaking sensor. Just to test it and rule out a fuse or other wiring problem beyond the one in the TSB, I probed the power and ground wires at the sensor and found they were OK. These are the wires on the outside of the connector. The center wire is a signal wire going to the controller and as far as I could tell it not able to be tested with a meter.
So all signs were pointing to simply a failing G395 sensor. It took me about 4 hours to get to this point - hopefully if you are reading this you can get to here in less time than it took me.
If you Google 'Audi G395 sensor' you can find these things all over the 'net - apparently they are a common failure item. The P/N for the one for my Q5 was 4H0-959-126-B (the last letter is the revision code - when you read this it may be updated to a later revision). Also, the TSB says to replace the seal - P/N 7H0820896.
I ordered new parts factory original parts off the 'net. I chose to get genuine factory parts vs. OEM aftermarket. They came in VW/Audi packaging so I am pretty sure I got the real deal. My experience with electrical parts like sensors is you get what you pay for. Total for parts was $70.
The old sensor on my Q5 has a Schrader valve underneath it and the way the seal is designed, you really only lose a tiny amount of refrigerant when you remove the old one - not even enough to worry about at all. This may not be the case for every model - but if you go to the Audi factory parts diagram at parts.audiusa.com and look at the diagram for your specific model, if it shows a valve under the sensor, then you should be OK to change it without losing the gas. If there is no valve shown, you may be in for a surprise when you go to unscrew the old sensor.
I used a small Crescent wrench and carefully loosened the old sensor - it is not on there that tightly. You will probably get a little oil squirt out with the refrigerant - this is normal. Leave this oil on the threads because it will make getting the seal off and on easier.
The seal on mine was purple in color (both old and new) and pretty easy to see. it just pulls off over the threads and the new one slides down. It is hard to slide it over the threads since it is a little snug, but be careful and you can work the new one all the way down. Main thing is to not tear or damage it when installing it.
Screw on the new sensor, snug it down with the wrench, re-attach the wire and enjoy your A/C!
Recently the A/C on my Q5 stopped working and I spent a half of a day troubleshooting it and scratching my head. In the end it was a simple fix but along the way I discovered that a lot of Audis have a common failure mode for A/C. Also, there was a lot of questions I had to dig into so I figured I would post my findings in the hopes it would help out others.
First, let me say that if you find this post because your A/C stopped working and you don't own a VAGCOM, then you should really get a VAGCOM. Assuming you are trying to do your own A/C repairs, you likely also do other repairs for which one of these is indispensable. I have no connection to the company, just a happy customer.
Second, assuming you have a VAGCOM, if your failure is like mine it is pretty easy to fix and you don't necessarily need a lot of specialized A/C repair tools.
Third, there is a TSB out that covers the symptoms - its number is 2020124 and is on the 'net several places. But I encourage you to find the most recent copy since it has been updated 13 times (as of today) to add more info. I have an Alldatadiy subscription and it is on there.
OK - here goes...
So the A/C just stopped working - blew hot air, compressor did not appear to be running.
First thing I did was pull out the VAGCOM and pull the codes and discovered the following:
00256 - A/C Pressure/Temperature Sensor (G395)
008 - Implausible Signal
This is where you need to get the TSB and follow its suggestions because if the 00256 code appears in concert with a 01592 code, the problem is most likely a cut wire that is common to the G395 sensor and a G238 sensor. I can't speak to how hard it is to chase down this broken wire since I did not have to do it. But I am sure it is fun...
The TSB also mentions that older versions of the G395 sensor were prone to leaking refrigerant. The G395 sensor on my Q5 is between the grill and the evaporator core on the driver's side. Since it was bone dry, I doubted it was leaking - refrigerant leaks almost always cause an oily spot where it leaks and mine had no oil at all on it anywhere. If yours appears to have oil on it, it has likely leaked down and not only requires replacement but also recharging of the system. This definitely requires a lot of special tools to do right so this would be a good time to seek professional help...
I did not have the 01592 code so I did not suspect the wiring was at fault. And since it was dry, I did not suspect a leaking sensor. Just to test it and rule out a fuse or other wiring problem beyond the one in the TSB, I probed the power and ground wires at the sensor and found they were OK. These are the wires on the outside of the connector. The center wire is a signal wire going to the controller and as far as I could tell it not able to be tested with a meter.
So all signs were pointing to simply a failing G395 sensor. It took me about 4 hours to get to this point - hopefully if you are reading this you can get to here in less time than it took me.
If you Google 'Audi G395 sensor' you can find these things all over the 'net - apparently they are a common failure item. The P/N for the one for my Q5 was 4H0-959-126-B (the last letter is the revision code - when you read this it may be updated to a later revision). Also, the TSB says to replace the seal - P/N 7H0820896.
I ordered new parts factory original parts off the 'net. I chose to get genuine factory parts vs. OEM aftermarket. They came in VW/Audi packaging so I am pretty sure I got the real deal. My experience with electrical parts like sensors is you get what you pay for. Total for parts was $70.
The old sensor on my Q5 has a Schrader valve underneath it and the way the seal is designed, you really only lose a tiny amount of refrigerant when you remove the old one - not even enough to worry about at all. This may not be the case for every model - but if you go to the Audi factory parts diagram at parts.audiusa.com and look at the diagram for your specific model, if it shows a valve under the sensor, then you should be OK to change it without losing the gas. If there is no valve shown, you may be in for a surprise when you go to unscrew the old sensor.
I used a small Crescent wrench and carefully loosened the old sensor - it is not on there that tightly. You will probably get a little oil squirt out with the refrigerant - this is normal. Leave this oil on the threads because it will make getting the seal off and on easier.
The seal on mine was purple in color (both old and new) and pretty easy to see. it just pulls off over the threads and the new one slides down. It is hard to slide it over the threads since it is a little snug, but be careful and you can work the new one all the way down. Main thing is to not tear or damage it when installing it.
Screw on the new sensor, snug it down with the wrench, re-attach the wire and enjoy your A/C!
08-18-2017, 02:41 PM
#3
AudiWorld Senior Member
RobTheAudiOwner You should be proud of yourself. I'm a certified Ac.tech, used to own a Napa garage.I'd hire you but you wouldn't be happy with salary ! What you've demonstrated in your description of the process is how thorough and methodical you have to be servicing the modern vehicle.I sold my business because I could no longer deal with the customers who I knew considered me a crook because diagnostics could often run up a substantial labour bill, and I was honest and often underbilled for this type of work.
08-23-2017, 05:43 AM
#4
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Thanks for the kind words.
I am blessed to be able to (and have the means to) do most of my own maintenance work and could not do it without the help of forums like this one. I feel bad sometimes because I am a net taker of info and rarely have the time due to my day job and other commitments to contribute. But when I come across something that can help others I like to provide it.
MurrayA4 I hear you on the labor rate issue. I used to wonder how shops could charge so much and then started buying my own tools and after realizing how much a shop has to spend on special tools in order to work on modern cars I stopped wondering. Scanners, programmers, A/C tools, etc. - those things are not free by a long stretch!
I am blessed to be able to (and have the means to) do most of my own maintenance work and could not do it without the help of forums like this one. I feel bad sometimes because I am a net taker of info and rarely have the time due to my day job and other commitments to contribute. But when I come across something that can help others I like to provide it.
MurrayA4 I hear you on the labor rate issue. I used to wonder how shops could charge so much and then started buying my own tools and after realizing how much a shop has to spend on special tools in order to work on modern cars I stopped wondering. Scanners, programmers, A/C tools, etc. - those things are not free by a long stretch!