Need some help with trouble shooting: I own a 1994 Audi cabriolet convertible. Runs great. Recently, during an extreme cold day O degrees, my engine got hot around 3/4 on gauge. Lots of bubbling hot water. Since I have owned it, though, the heat has never worked. A.C works fine and is very cold. never overheats. my gauge never gets above half way. One mechanic suggested I replace my water pump and timing belt. But it was done already 20k ago. I emptied the antifreeze and replaced with fresh antifreeze/distilled water. Running fine but absolutely no heat.

Suggestions?

 

The is a vacuum operated valve at the back of the engine in-line with one of the hoses that runs to the heater core. If it's not working, it's not allowing water to circulate into the heater core. It's very easy to replace if that is the culprit. The vacuum line to it could be unplugged too. That system gets vacuum from pump, not the engine intake.


Also, another thing could be the Climate Control, mainly the servo that controls the tempurature flap, is not moving. My Audi 5000 had stripped gears in the little stepper motor that moved the cable. I'd have to reach in over the glove box (open) and push it over with my finger. Then it would catch and start moving.

HTH,
Dave

 

Sorry dave, there is no vacuum operated valve such as you describe. The cabriolet always has coolant flowing through the heater core and relies on the diverter doors in the heater box to control hot and cool air. While I wish I had such a valve on my Cab, and it would make sense, Audi did not install it. Degradation of the foam on the heater box doors is why the cold air conditioned air gets diluted somewhat with the hot air as the car ages. It is terribly frustrating and I am figuring that rado's heater core has been bypassed. That's why his cold air is really cold and he has no heat. Rado, check at the midpoint of the firewall and look to see if you have the two heater core tubes poking out. By the way, I hope you used G-11 or G-12 and not prestone when you drained and refilled. Also, the system has to be bled of air or you will get a vapor block and you will overheat, just like it did when the temp went to 3/4 gauge. The easiest bleed point is, you guessed it, on the $50 hose that goes to the heater core and is plainly visable at the firewall. Let us know what you find. Go to 12v.org and read up in the How-to's for head gasket replacement to see how to bleed the air out.