Heater control failure

[dekonstruct]

My friends A4 has a heater control problem.

When she turns on the A/C the heater turns on full blast and will not switch over to cold air. Anybody experienced this?

Also how does the system disassemble? I've never taken the dash apart in an Audi before just Chevy, Chrysler, and Ford cars. My guess is it's a vacuum line to control the temperature valve. But that would be on a Chevy... No idea how Audi works.

[brewmastr]

do our cars use duo valves? ive never looked, lol i look through this forum and its remarkable how problem free my audi has been that im not sure how our systems work entirely, anyhow, bmw and mercedes uses duo valves to control heater inlet, im not sure if audi uses blend door to mix hot and cold, but my point here is that if we do you duo or even mono valve to control heat flow to the heater core when they go bad the at rest state of it is full heat, so if the heater control like says its going to LO but its still hot it could be a duo valve problem or if we use blend air door to control that, diagnosticator or old guy can answer this better im just babbling here, anyhow i doubt its the control head if its ok, basically trace the coolant lines that go to the heater core, if there is an electric valve in between on of the hoses and the heater core that is a duo or mono valve replace that, if not you probably have a stepper motor for the blend air door that has gone bad and need to replace that, those are pretty easily accessible by removing the glove box, i just did one on my car, was rather easy.

[diagnosticator]

My friends A4 has a heater control problem.

When she turns on the A/C the heater turns on full blast and will not switch over to cold air. Anybody experienced this?

Also how does the system disassemble? I've never taken the dash apart in an Audi before just Chevy, Chrysler, and Ford cars. My guess is it's a vacuum line to control the temperature valve. But that would be on a Chevy... No idea how Audi works.

The air temp is controlled by mixing cooled and heated air, using servo motors to shift the air flaps accordingly. There are air blend flaps, and flaps to direct airflow to the varios outlet vents. To determine the problem, have the A/C controller scanned for DTCs.

[dekonstruct]

Interestingly... I haven't seen this problem w/ such a low mileage car.

It turned out to be a leak in the A/C lines. We haven't isolated it yet. She wanted it fixed right away and I didn't have a pressure gauge to check if it needed new fluid so we took it in.

They charged her $98!!! and all they did was add a die and little freon. Give me a break like 2 minutes of work and $10 in fluid.

So my next step is... I'm just going to fix the leak should it show up. Do you guys know where I can price A/C parts for this car? Or know of any diagrams I could see that show the components in the A/C system.

Thanks!