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sprinkles08, ASE Certified Technician
Category: Audi
Satisfied Customers: 22822
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I have 2004 audi a8l with ac&heat control unit problem. When

Customer Question

Hello i have 2004 audi a8l with ac&heat control unit problem. When ignition put on the digits on hvac unit show up for 2 sec than goes off. Nothing works. So no heat, no ac , no seat warmers..its dead. Any help? Thx
Submitted: 1 year ago.
Category: Audi
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

This is most likely being caused by an internal failure in the control head if there are no other problems at the same time. The problem is either the control head itself or a lost power or ground to it. If it consistently powers up initially and goes back off it's not likely to be a lost power or ground, especially due to a wiring issue.

What will need to be done is test the power and ground feeds to the control head at the time it won't work. If they are present then the control head can be condemned.

Customer: replied 1 year ago.
Hello thx for reply..i ordered used hvac control unit of ebay and tryed it. It does the same thing. I dont think problem is unit itself. Fuses all good. What happens is first time you turn ignition on everything lights up and works for maybe 2 secs. After couple tries it doesnt want to light up at all...and another thing my mmi controls are dead to, but i dont think those 2 are conected?
Customer: replied 1 year ago.
Also if you disconect hvac unit, the ac fans in engine bay turn ac clutch engages..
Expert:  sprinkles08 replied 1 year ago.

Have you tested the powers and grounds while the unit will not operate?