awdinut

I had the inidie tech R&R my heater control valve with a used (unfortunately not a 'known good' unit) unit from a yard. I dont know if it is working or not...but I still dont have ANY heat. Cant get even warm air from vents on a 50 degree day.

When I put my hand on the two piston covers of the heater valve unit as the climate control is set to HI, they are hot, and I feel vibration that periodically stops for a moment. And the two small hoses on the bottom are hotter that the two top hoses.

The tech ran the diagnostic procedure with the VAG-COM and says that there is a door with a servo that is labeled 'TEMPERATURE', and that said door does not respond to the VAG-COM. But more than that he can not tell me and says he doesnt understand how the system functions to achieve heat. He did give me a print out of the diagram of the HVAC sytem and a legend to identify the various parts...but it all means nothing to me.

Where do I go from here ? Are there any clues in this missive that gives one of you an idea ? I could fabricate a manifold out of sweated copper tubing that would put the hot water in the heater cores full blast. But that would be quite a piece of engineering and work...I'd rather get the system functioning as intended.

MP4.2+6.0

My guess from your description is a heater flap door. The flaps (a variety of them) direct the air flow. Yes, you test those with VCDS. You can see codes of course, plus there is a test routine as I recall to move each one sequentially.

If door doesn't do its thing, fan can't blow air past inside heater core (s). Dealing with it consists of VCDS diagnostics (and also trying to pin down is it one or both sides since there are two heater cores), and then typically an under dash disassembly dive. I haven't had to deal with them since my 1985 Audi 5000, so no recent hands on experience with the doors themselves.

mishar

+1

This may help:

Mister Bally

Very simple, non-complicated assembly. Easy to access as well.

mishar

+1 on that too.

the_duke

It could be an actuator or it could be a temperature probe reading wrong on therefore not telling the HVAC controller to provide more heat. It's complicated system. But if you spend some time going through HVAC with VCDS you will find all the temp probe readings etc. That the only way I can think for you to determine the problem. It would be good to know exactly what servo labeled "Temperture" he was talking bout. It should have a number corresponding to the diagram above. Give me a few minutes and I'll try and find the link for the HVAC self study.

awdinut

The exploded view shows many doors that direct the warm air to the various outlets. But would not a failure of any of those doors would mean no heat to a given outlet or set of outlets; I have no heat coming out of ANY outlet. And I see no door who's function it is to let hot air out of the heater core(s). What am I missing ?

The tech says that V68, refered to as 'temperature regulator flap motor' in the print out he gave me, was the one that did not respond to the VAG-COM. But in the explosion its refered to as a 'CHEST WARM AIR' motor, which , by the sound of it, would not affect ALL the outlets. Can anyone provide clarification about this?

I really have no confidence that the Audi dealer techs would have any knowledge about a 2004 A8 heating system or be able to diagnose the problem. Am I right ?!

dvs_dave

Just pop out the ashtray, one torx screw, and a couple clips in the footwells and it slides right out.

Mister Bally

Installation is the reverse of removal

mishar

Few of those flaps are in pairs but actuated by a single motor. First one on top for example. Your technician probably missed some and found one not crucial. I think you can check the top one without removing much. May be fan?