2002 Audi allroad 2.5tdi HVAC issues

[skyegtb]

2002 Audi allroad 2.5tdi HVAC issues


Hello, I am currently fault finding some issues with the above car and am kind of stumped at the moment. Firstly, I apologise that this will be a long post but I want to include all the info and steps I have done so far.


So, initially I will explain the problem. The way the car was before i started investigating was that every aspect of the HVAC system worked as it should - no solid 'ECON' light was displayed and all functions worked, APART from no cold air from the system and no triggering of the AC clutch. There was also one fault code: 01582 - Signal for Coolant Temperature 30-00 - Open or Short to Plus


Below is the full fault code scan - clean bill of health apart from the HVAC.


Chassis Type: 4B (4B - Audi A6/S6/RS6/allroad C5 (1998 > 2005))
Scan: 01 02 03 06 08 15 16 17 18 22 34 35 36 37 45 55 56 57 65 67
75 76 77

VIN: WAUZZZ4B12N117666
-------------------------------------------------------------------------------
Address 01: Engine Labels: 059-907-401-AKE.clb
Part No: 4Z7 907 401 B
Component: 2.5l/4VTEDC G000SG D06
Coding: 01015
Shop #: WSC 02325
VCID: 3C7CE95B2C6BA0A2D5-4B00


Subsystem 1 - Part No: 00017059
Component: 130 106EC150_1.R75775723283
WAUZZZ4B12N117666 AUZ7Z0B2054918


No fault code found.


-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8D0-907-389.lbl
Part No: 4Z7 907 389 A
Component: ABS/ESP allrad D55
Coding: 06455
Shop #: WSC 00665
VCID: 4A90BF8376BF0E1257-5120


No fault code found.


-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 4B0-820-043-MY1.lbl
Part No: 4B0 820 043 H
Component: A6-Klimavollautomat D64
Coding: 00064
Shop #: WSC 02335
VCID: 1F463ED79DBDDBBAD0-2586


1 Fault Found:
01582 - Signal for Coolant Temperature
30-00 - Open or Short to Plus


-------------------------------------------------------------------------------
Address 15: Airbags Labels: 4B0-959-655-AI84.lbl
Part No: 4Z7 959 655 D
Component: Airbag 8.4E 5000
Coding: 0001106
Shop #: WSC 02325 785 00200
VCID: 50A4ADEBC0E334C219-513C


No fault code found.


-------------------------------------------------------------------------------
Address 17: Instruments Labels: 4B0-920-xxx-17.lbl
Part No: 4B0 920 981 JX
Component: KOMBI+WEGFAHRS. VDO D12
Coding: 04460
Shop #: WSC 00665
VCID: 050A4CBF1F21216AFA-513C
WAUZZZ4B12N117666 AUZ7Z0B2054918


No fault code found.


-------------------------------------------------------------------------------
Address 34: Level Control Labels: 4Z7-907-553.lbl
Part No: 4Z7 907 553 E
Component: - 2C1A1 D040
Coding: 25500
Shop #: WSC 09999
VCID: 479686B765ADF37A48-5120


No fault code found.


-------------------------------------------------------------------------------
Address 35: Centr. Locks Labels: 4B0-962-258.lbl
Part No: 4B0 962 258 K
Component: Zentralverrieg.,DWA D35
Coding: 04939
Shop #: WSC 00873
VCID: 3162C86FFB295DCA76-4ECA


No fault code found.


-------------------------------------------------------------------------------
Address 45: Inter. Monitor Labels: 4B0-951-173.lbl
Part No: 4B0 951 173
Component: Innenraumueberw. D03
Coding: 00002
Shop #: WSC 02325
VCID: 60C47D2BE043A442A9-4B32


No fault code found.


-------------------------------------------------------------------------------
Address 55: Headlight Range Labels: 4Z7-907-357.lbl
Part No: 4Z7 907 357
Component: dynamische LWR D07
Coding: 00030
Shop #: WSC 02325
VCID: 040C51BB141B1862ED-4B18


No fault code found.


-------------------------------------------------------------------------------
Address 56: Radio Labels: 8E0-035-1xx-56.lbl
Part No: 4B0 035 186 G
Component: concert II GRO 0008
Coding: 00201
Shop #: WSC 00000
VCID: 244C313BB4DBF8628D-4AE6


No fault code found.


So, with that fault code I did some Googling, but didn't find much of help, apart from some info that the control unit in the dash most likely housed this sensor. I then did some VAGCOM'ing and noted that when scanning the system -40°C appeared on the dash temp display and also in Group 11 -40°C appeared. Googling that basically told me that this would prevent the air conditioning from starting up as the system already thinks it is sub zero! Of course this does not help me much either, so I did more digging and found a suggestion that the control unit in my car was designed for pre-2002 models and if fitted to post 2002 cars the fault code and -40°C issue would be the likely result. I searched the part number 4B0 820 043 H and true enough there is a lot of evidence that suggests this is pre-2002. Also the date sticker on the unit itself is from year 2000. Also of note is that this unit did not match the rest of the dashboard - it was black with regular smooth plastic buttons, yet the rest of the dash in this car is of the 'soft' easy worn material and the buttons on the stereo are very worn.


With the above info I went online and tried to find a post-2002 control unit. I found a 4B0 820 043 AQ which according to ETKA online should be suitable for a 2002 car. Today this unit arrived so I fitted it to the car. I had to change the coding from 00104 to 00004 initially as I was getting a coding error - presumably related to the fact that this car has a magnetic clutch on the AC compressor, but after that was done I ran all the VAGCOM tests and checked measuring blocks etc and all appeared to be OK, but on this unit the ECON light was on solidly. I checked for fault codes and this unit came up with:
2 Faults Found:
00819 - High Pressure Sensor (G65) 29-00 - Short to Ground
01592 - Air Quality Sensor (G238) 57-00 - Electric Circuit Failure


Anyway, I stopped there as I am bamboozled about a number of things. Why do both units operate the entire system without issues apart from neither will actually activate the air con compressor? Is the coding correct on both of these units? When coding, what does the Shop# mean on VAGCOM? Why do the fault codes from the 2nd unit not appear with the original one? And finally, does the pre-post 2002 issue with these units actually relate to allroads on not?


Thanks for reading my very long post, and if you have any advice to offer - I am all ears! Thanks in advance!

[Audibot]

Neither actuated the a/c probably for the reasons you listed. The old one did its temperature check, which said it was already too cold to turn on. The 2nd one says your a/c pressure switch is broken, which will also prevent the a/c from coming on. It's likely your pressure switch was broken the whole time but the system masked it.

Strangely enough last year I could not even talk to my module at first and so could not troubleshoot my HVAC myself for a time. Eventually an update from Ross-Tech helped, but still...

Replace the refrigerant high pressure sensor/switch and you should be good to go (side of condenser).

[skyegtb]

Neither actuated the a/c probably for the reasons you listed. The old one did its temperature check, which said it was already too cold to turn on. The 2nd one says your a/c pressure switch is broken, which will also prevent the a/c from coming on. It's likely your pressure switch was broken the whole time but the system masked it.

Strangely enough last year I could not even talk to my module at first and so could not troubleshoot my HVAC myself for a time. Eventually an update from Ross-Tech helped, but still...

Replace the refrigerant high pressure sensor/switch and you should be good to go (side of condenser).

Many thanks for your reply. I believe you are correct, and this was the same conclusion I came to earlier, so: Another update, as I am just back in from the car - I removed the G65 pressure sensor, it was split where the metal is swaged on to the plastic 3 pin connector end and quite definitely broken, I guess that all the gas in the system probably escaped past the split in this sensor. I then remembered that I had a DIY air con pressure tester. I connected it up to the low pressure port and there was zero psi of gas pressure there. So, I will be buying a new sensor and getting a re-gas done. The part number on my old sensor is 8Z0 959 126 DRH (not sure if the DRH has anything to do with the part number though). After lots of internet searching I am not sure what part number i need for the new sensor as this part was long ago superseded. I *think* that the Hella part 6ZL 351 028-401 should be correct, but I do not want to order one until I have it confirmed as I have read of many people struggling to get the correct replacement part here!

If anyone can confirm the correct part number for me it would be greatly appreciated.

[Audibot]

Yeah, similar to you, mine was damaged, and when the shop went to remove it, it literally SHOT off the condenser and flew across the shop. Took a piece of the condenser along with it, so I needed a new one of those.

You have an 02, which I think they changed the part number (at least here in America, where it is 3R0959126). I think the "D" is the revision and the "RH" is right-hand drive, being in the UK. Probably to facilitate some kind of arrangement. I'm not sure though. I know in the US we can scope out different dealership websites and see. Or call them up.

[skyegtb]

I have emailed my local Audi dealership to confirm the correct part. I will post back here after I have got it fitted. Thanks again for the assistance.