Heater Problem

[Michael Veglia]

<< I've got a '99 A6 that's not getting any heat.  I had the heater 
core flushed last year that helped some but only for a short period of time but 
before the 
winter was over I was getting no heat again.  The shop said I needed a new 
heater core.  Forgot all about it then as from March to November unless it's 
raining I'm on my bike not in the car.  Just took the car to a different shop 
and they say the core is not blocked.  They say water pump is not pumping 
enough to meet the needs of the engine cooling system and still push 
coolant through the heater core unless the motor is turning at least 2,000 to 
2,500 rpm, which it almost never does in local driving.  With the motor at 
proper temps, reving it in idle to 2,500 rpm did get hot air out of the heater 
vents.  The water pump had been replaced 35,000 miles ago when the 
timing belt was changed.  Does this make sense, that the water pump is the 
cause of the lack of heat? >>

I really doubt it is the water pump, if it were really that bad I would think 
you would have overheating issues. 

The HAVC system is a blended air type system. I haven't worked on the C5 chassis 
systems yet, but AFAIK they are similar to the C4 chassis in principle 
(component layout is different--it appears much easier to service the blower in 
the C5, for example). These systems are an evolution of the vacuum flap 
controlled systems from the type 44 days. They now use electric flap actuators. 
The flap motors develop dead spots and hang up. Symptoms include no heat (or no 
cold), and air not coming out of correct vents. It has been a while since I had 
to deal with this on the C4 so my memory is hazy, but I think there are 3 or 4 
of these motors. One of them controls the hot/cold air blending flap. On the C4 
that is the easiest to access (on top of the front of the HVAC unit, accessible 
by removing the plastic shroud in front of the windshield) and replace. The 
climate controller has very good diagnostics, pulling the codes will tell you 
what is wrong when the flap motors fail. I have not yet been down this road on 
our '01 allroad, but it looks similar to the C4.

Find a local "friend" with VAG-COM and pull codes from the HVAC controller is a 
good place to start.

HTH

Mike Veglia