Wayyyyyy back, on my 2001 Golf TDI, it was maybe five years old, but possibly less. The aircon ECU failed. All I could get was arctic blast, or open hot oven door. It was the fancy push button version. No knobs.........
Anyway, the dealer told me they would have to strip the dash to get access to determine the fault, so an immediate cost. To be fair to the dealer, at the end you could not tell it had been touched. Maybe it hadn't.........
So they got inside and declared it was the aircon brain. They could either reassemble and charge me whatever and I would be no better off, or replace the brain. The bill for that was £850. In 2005/6.