I’ve recently purchased a 2004 A3 (8P), and have a fault with the AC.
The Econ light is on for most of the time, even with the system in “auto” mode. Checking the owner’s manual confirms that there is a fault with the AC system. But sometimes, the system appears to work, and just the Auto button is illuminated, but the air is not chilled when you go down to the lower temperature settings. Going from Auto, to Econ and back again when the system appears to be working I can’t hear the compressor clutch engaging, nor does the larger electrical fan on the radiator engage.
I have managed to borrow VAG-Com, and there are no stored fault codes for the HVAC system. I have run through the self tests and they all seen to pass ok.
I am good at diagnostics/fault fining, but this one is foxing me.
Any thoughts, guidance, additional tests I can run would be really appreciated.