HEAT PROBLEMS

[mr.spoolin]

I have a 97 Audi a8 and it is not putting out any heat. when i turn it to auto and turn both sides to HI the fan only turns on one bar and doesn't put out any heat on the drivers side and a very little bit of heat on the passanger side. I went under the hood and the 2 hoses coming in to the fire wall with the top bleeders on them on the driver side, both of them had good flow out. I didnt check temp on them but there is fluid coming out of both.

[Prospeeder]

theres a temp sensor on the heater core. if the heater core temp is low, it will turn the fan speed down untill core temps are higher. Sounds like the core is clogged, and not transferring heat like it should. i see it all the time, they "seem" to flow fine but they really dont, if you cut a core open to see whats inside, you will see why they clog and how water still just flys on by

[silverd2]

Originally Posted by mr.spoolin

I have a 97 Audi a8 and it is not putting out any heat. when i turn it to auto and turn both sides to HI the fan only turns on one bar and doesn't put out any heat on the drivers side and a very little bit of heat on the passanger side.


I went under the hood and the 2 hoses coming in to the fire wall with the top bleeders on them on the driver side, both of them had good flow out. I didnt check temp on them but there is fluid coming out of both.

I have NEVER heard of a clogged heater core on a D2 A8, unless "maybe" someone has used a lot of stop-leak (always a really bad idea) or mixed the wrong coolant with pink G-12, enough to show lots of thick brown sludge (caused by that mix) in the reservoir.

A8 heater systems are different from most other cars and other Audi's in a couple of ways. They have 2 heater cores for dual climate zones. The flow of coolant to both cores is electrically controlled by the pump/valve unit, next to the brake booster in the fresh air plenum. That same unit is the one that runs the restore function on your climate control...temporary heat function after engine is shut off. That unit can be fouled by a bad mix of coolants...ANY coolant mixed with pink (or purple) G-12, no matter what the label says, makes a corrosive clogging brown sludge.

If both heater hoses are equally hot when heat is set to max, then coolant is likely flowing OK through the cores. If the upper left hose (return from cores) is noticeably cooler than the lower right (hot supply from back of heads), then coolant is not flowing through the cores...In an A8, this usually caused by a problem with the pump/valve unit (VERY expensive unit), NOT a clogged core.

If both hoses are equally hot, then your problem is likely in the controls inside the car...bad sensor maybe or more likely temp control flaps (or motors) stuck or failed. Without a major disassemble, only a VagCom diagnostic (which reads every little sensor, motor and flap) will pinpoint the problem. A simple code reader (like at Advance or Autozone) will tell you nothing...they can't read the climate control module.

[mr.spoolin]

started tearing in to it a little this morning and the resevor is full of a dark brown sluge, was gonna see if i should do a flush or tear in to that dual climate pump?

[morpheousx]

Looks like silverd2 was on the money with his diagnosis.

[silverd2]

Originally Posted by mr.spoolin

started tearing in to it a little this morning and the resevor is full of a dark brown sluge, was gonna see if i should do a flush or tear in to that dual climate pump?

I would do NO less than a full chemical flush of the coolant circuit...then see how things are before attempting anything with the pump valve unit. I've seen in the past that a simple water flush or coolant change is NOT near enough to clean out the contamination.
I would also follow the flush with a Vagcom reading, then erasing of all codes ...if any.