My air conditioning works, however when I change the temperature setting to say something that should give me heat, like a 25 degree celsius setting, I do not get any heat. It seems to blow the same cold temperature no matter what setting you put the temperature setting on to.

However, occassionally I will get heat. One time after driving on the highway for about a half hour, I got home and decided to try the heat and see if I could get any. Sure enough, heat came out.

The symptoms are not related to the car not being warmed up. The engine temperature is pin straight on the 90 degree mark, and never moves.

If I replace the whole hvac control unit in the dash do you think that could fix it?

Like I said, on occassion I get heat, but not reliably. Does the head unit control the flaps or dampers?

Thanks for the input.

 

Do you have access to a VAG-COM? The HVAC system on these cars is fairly complex with multiple sensors and multiple solenoid-driven flaps. A quick scan with a VAG-COM should point you to the problem.

The temp mix solenoid frequently fails as it is in constant motion. I was able to remove mine, clean it up and reuse it - but it is a pain to get to. Note that I was able to get to it by removing only the glove box assembly, didn't require removal of the complete center console. There is a great writeup in the FAQs, but good luck finding them.

 

I vag the car when I get the cable back from a friend. I have vag it before with the issue at hand, and did not notice anything in particular on the scan. But I am not very good at utilizing the information yet. Still a newbie.

I will dig up my old scan and see if there is anything there.

Do you know if replacing that head unit could solve the issue of the temperature control?

 

what type of search query should I use to find in the FAQ?

 

Here is the last VAG done on the car. This scan was done a while ago, but the problem existed back then. Where do you find out what the fault codes mean?

Monday,27,April,2009,19:24:17:14119
VCDS Version: Release 805.3
Data version: 20090213



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 8D - Audi A4 B5
Scan: 01 02 03 08 15 16 17 25 35 37 45 55 56 57 67 75 76 77

Mileage: 135940km/84469miles
-------------------------------------------------------------------------------
Address 01: Engine Labels: 4B0-906-018.lbl
Part No: 4B0 906 018 CH
Component: 1.8L R4/5VT G 0001
Coding: 16751
Shop #: WSC 63351

No fault code found.
Readiness: 0010 1101

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: 8D0-927-156.lbl
Part No: 8D0 927 156 DF
Component: AG5 01V 1.8l5VT USA 1010
Coding: 00002
Shop #: WSC 63351

1 Fault Found:
18258 - Can't Decode, CODE File Not Loaded!
P1850 - 35-10 - Can't Decode, CODE File Not Loaded! - Intermittent

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8D0-907-389.lbl
Part No: 8D0 907 389 E
Component: ABS/ESP allrad D56
Coding: 04277
Shop #: WSC 06435

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: Redir Fail!
Part No: 8D0 820 043 P
Component: A4 KLIMAAUTOMAT D58
Coding: 00040
Shop #: WSC 63351

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 8D0-959-655-AI8.lbl
Part No: 8D0 959 655 G
Component: Airbag Front+Kopf 1002
Coding: 00304
Shop #: WSC 63351

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 8D0-920-xxx-17.lbl
Part No: 8D0 920 932 K
Component: B5-KOMBIINSTR. VDO D12
Coding: 02344
Shop #: WSC 93250

1 Fault Found:
01314 - Can't Decode, CODE File Not Loaded!
49-10 - Can't Decode, CODE File Not Loaded! - Intermittent

-------------------------------------------------------------------------------
Address 35: Centr. Locks Labels: 8D0-862-257.lbl
Part No: 8L0 862 257 N
Component: CV-Pump, Alarm, RC D16
Coding: 16140
Shop #: WSC 63351

9 Faults Found:
01367 - Can't Decode, CODE File Not Loaded!
35-00 - Can't Decode, CODE File Not Loaded!
01371 - Can't Decode, CODE File Not Loaded!
35-00 - Can't Decode, CODE File Not Loaded!
01374 - Can't Decode, CODE File Not Loaded!
35-00 - Can't Decode, CODE File Not Loaded!
01370 - Can't Decode, CODE File Not Loaded!
35-00 - Can't Decode, CODE File Not Loaded!
01369 - Can't Decode, CODE File Not Loaded!
35-00 - Can't Decode, CODE File Not Loaded!
01368 - Can't Decode, CODE File Not Loaded!
35-00 - Can't Decode, CODE File Not Loaded!
00991 - Can't Decode, CODE File Not Loaded!
28-00 - Can't Decode, CODE File Not Loaded!
00955 - Can't Decode, CODE File Not Loaded!
09-00 - Can't Decode, CODE File Not Loaded!
00956 - Can't Decode, CODE File Not Loaded!
09-00 - Can't Decode, CODE File Not Loaded!

-------------------------------------------------------------------------------
Address 45: Inter. Monitor Labels: 4B0-951-173.lbl
Part No: 4B0 951 173
Component: Innenraumueberw. D03
Coding: 00101
Shop #: WSC 63351

No fault code found.

-------------------------------------------------------------------------------
Address 55: Xenon Range Labels: 4B0-907-357-AUT.lbl
Part No: 4B0 907 357
Component: LEUCHTWEITEREGLER D004
Coding: 00012
Shop #: WSC 63351

1 Fault Found:
00776 - Can't Decode, CODE File Not Loaded!
31-00 - Can't Decode, CODE File Not Loaded!

-------------------------------------------------------------------------------
Address 56: Radio Labels: 8D0-035-1xx-56.lbl
Part No: 8D0 035 195 A
Component: Radio D00
Coding: 00110
Shop #: WSC 63351

No fault code found.

End ---------------------------------------------------------------------

 

[QUOTE=jstnvndn;23837125]
Address 08: Auto HVAC Labels: Redir Fail!
Part No: 8D0 820 043 P
Component: A4 KLIMAAUTOMAT D58
Coding: 00040
Shop #: WSC 63351

No fault code found.

----------------------------------------------------------------------------QUOTE]

I'm not sure what "Redir Fail!" means, but it appears as though the VAG-COM is connecting with the Climate Control head unit (or maybe not?). Perhaps someone with more VAG-COM expertise can help here.

My VAG-COM usually takes several tries to connect to the Climate control head unit, but connects almost immediately to the other boxes that I look at, i.e. the engine ECU. It might be worthwhile to rescan the Climate Control box only and make sure that it connects properly. If it can't connect, you can suspect the control unit.

If the control unit box is connecting and reporting no faults, I have doubts on whether replacing the unit will do any good, but it certainly looks that way.

 

Here is what "redir Fail!" might mean: https://www.audiworld.com/forums/sho...ght=Redir+Fail

I have to question the applicability of a scan from last April (just noticed this piece of info). Things change over time, parts wear out, things break. I believe that the Climate Control head unit may recalibrate itself regularly (seems to go through the motions with every startup of the car), so an intermittent problem may not show up every time. It's good that you are starting to look at this now, as I can't imagine a winter in Winnepeg without working heat - this is what prompted me to fix my problem last November, and I'm in the relatively tropical Chicago area.

It would serve you well to either get a rescan or get a VAG-COM tool and rescan it yourself. Note: I use a "shareware" version of VAG-COM with an Ebay adaptor, gives me about 95% of what I need. If you have access to a spare control head, you can try it, but if you have to pay for it I believe that you are not going to solve your problem, at least based on my personal experience chasing the same issue - it was the temp mixture flap solenoid.

 

Well, I think I will try flushing the heater core first. Easy to do, and really it can't hurt anything...unless I blow the heater core.

If that doesn't work, I will try to rescan the car again with the VAG.

 

You can see if the heater core is passing coolant through it without flushing: the two hoses that run to the heater core from the back of the engine should both be hot, perhaps one is hotter than the other, but both will be hot if coolant is running through. The heater core is always "ON" and at full flow in an A4, the HVAC temperature is controlled by the temp control solenoid and flap, which mixes hot (air passing through the heater core) and cold (fresh or air-coditioned air) to the temperature that you specify. Of course if you are due for a coolant flush, please ignore.

 

I flushed the heater core. Not sure how much water pressure to use, so I played it safe with a very light flow out of the garden hose.
It ran clear out the other end after about a half a litre came through. It was pink to start out. The resovoir is also pink in color.

Still no heat.

I will try to get the vag to connect to the head unit. If it has a redirect failure, do I just try to reconnect again and again until it finally connects? I have a authentic vag tool, not the cheap one.