AC compressor not engaging VAG-COM codes...

[nowa]

Hi all happy A4 owners,

so the summer is upon us and I switched my AC on for the first time in a couple of months...
The AC button lit up and all but nothing happened, no sound (clutch or compressor noise) nor any drop in RPM like I'm normally used to and of course no cold air :(

So I stuck the VAG-COM tool in and this is what it came back with:

Address 08: Auto HVAC Labels: Redir Fail!
Control Module Part Number: 8T2 820 043 T HW: 8T2 820 043 T
Component and/or Version: KLIMA 3 ZONEN H06 0140
Software Coding: 34040000
Work Shop Code: WSC 06335 000 00000
VCID: 43814B3F7B05
2 Faults Found:


00457 - Control Module for Network (J519)
013 - Check DTC Memory
Freeze Frame:
Fault Status: 01101101
Fault Priority: 6
Fault Frequency: 1
Reset counter: 217
Mileage: 171785 km
Time Indication: 0
Date: 2014.12.14
Time: 16:25:43


00256 - A/C Pressure/Temperature Sensor (G395)
008 - Implausible Signal
Freeze Frame:
Fault Status: 01101000
Fault Priority: 7
Fault Frequency: 1
Reset counter: 217
Mileage: 171785 km
Time Indication: 0
Date: 2014.12.14
Time: 16:25:43


Freeze Frame:
Temperature: 29.0°C


Does anyone know what the problem could be? Are there any fuses to check, if so, does anyone know which ones? I'm wondering if it is worth refilling the gas or is it likely to be this G395 pressure sensor and if so, I assume changing this sensor will mean re-gassing is needed anyway right? Or is it possible that the pressure sensor is not getting a decent signal due to the lack of gas and as such it would be useful to re-gas first before changing any sensors?

Or am I totally wrong here and the problem lies with an expensive compressor change?

Please help...

Many thanks in advance

[Boy]

If the system is similar to that on the B6 A4, all that should be required is to change that sensor which will be located at one end of the A/C radiator. The good news is that you will not need to regas after changing the sensor as it screws in and there is a spring loaded valve behind it to seal the system.
On the B6, it is mounted at the left (n/s) end of the rad and can be accessed relatively easily. I have not changed one on a B8, but someone will be along soon who has and will tell us where it is.

[nowa]

If the system is similar to that on the B6 A4, all that should be required is to change that sensor which will be located at one end of the A/C radiator. The good news is that you will not need to regas after changing the sensor as it screws in and there is a spring loaded valve behind it to seal the system.
On the B6, it is mounted at the left (n/s) end of the rad and can be accessed relatively easily. I have not changed one on a B8, but someone will be along soon who has and will tell us where it is.
Many thanks for your reply! I will have a look to see if I can find the sensor on my B8

Would you say that it is the sensor that is at fault or could this VAG-COM error be generated by a lack of pressure and as such I should check the gas level first (which is by the way is something I dont know how to do...) ?

[nowa]

So I've done some more legwork on this and first of all, I've located my G395 sensor (part# 4H0 959 126)

On my Audi A4 Avant (B8) 2.0TDI, the sensor is located at the left side of the radiator (picture below, red circle is the location of the sensor which is currently removed) Note that a cover trim (4 screws) has to be removed first to see down to the radiator.
27780

Anyway, I also googled around a bit and I found this:

http://uberlame.com/a6_tsb/HVAC/Air%20conditioning%20inoperative%202020124-2.pdf

It would seem that some newer Audis have a problem with either this G395 sensor and/or that one of the wires (the purple one I think) from the sensor
is pinched or cut. That document above suggests 2 places where this wire might be pinched or cut... The confusing part is that the document refers to "the drivers side" when indicating the location of the 2 suggested places. I actually assumed that the document meant the left side, which in turn means "the passengers side" on UK cars. The reason I am assuming this is that one of the locations the document refers to is "under the drivers side headlight" and I found this location on my A4 under the left hand side (passengers side on UK cars) I looked at the wire harness there and it seemed ok. I also removed the left hand side door threshold trim and the wire harness looked ok there too, so I am assuming that I do not have a pinched or cut wire.

Is there any way to check if my G395 sensor is faulty?
Using a volt meter I tried to measure the resistance between the 3 pins on the sensor and I couldn't find a closed loop between any of them.
I also measured the voltage on the 3 pins on the connector to the sensor and it was 8V between the purple and ground and 12V between the 2 other wires so I am assuming things are ok there too. I'm just trying to get as much info as possible avoiding buying a G395 sensor if the problem is elsewhere...

[DNicK]

Hi

I had this same issue on my 1.8 TFSI last week. The compressor simply wouldn't come on and the error codes were similar to yours.

Turned out to be the A/C pressure switch had malfunctioned. Replaced it in 20 mins and is now back to normal.

[nowa]

Thanks for the reply...

Well, Ive ordered a new G395 sensor... Should be here in a few days, Ill update what happens after I changed it.

According to the document in my previous post, the old G395 sensor were leaking gas as well as being prone to failure and have since been upgraded, they now end with letter 'B' so might be worth while checking gas pressure...

[nowa]

Well, got my new AC preassure sensor and fitted it and the compressor is still not engaging... Ill check if the VAG error codes are the same but I guess next step is to check the gas preassure... I suppose I should have done that first after all...

[nowa]

So, after a regas its all good again and it looks like the sensor was broken as well as fitting the old one made the kompressor not engaging again

[Boy]

Glad to hear that all is sorted.
Perhaps the gas went because the faulty sensor prevented the compressor from running for too long and the seals shrank.
I believe a regular running is recommended to keep the seals tight.