Hope this can be of help to someone.

My son bought a 2000 C230K, 80k, as his first car. The wife has a 2000 C280, daughter has a 1999 C280, so I was hoping to only have to "learn" one car.

Wasn't but a month before AC crapped out. Not only hot air but hot air thru the vents even when the AC was not on.

Went to a local shop and he diagnosed the problem right away. Hi pressure was ice cold so the culprit was probably the heater valve. He said heater valves were a common problem for C-class of this vintage. He noted compressor was in good shape. They tend to turn "reddish" when they start to fail. This is the magnetic clutch burning up and leaving residue.

Looking at the repair, it would be a pretty easy DIY. Easy access, just three hose clamps and the rest just plug and play.

Dealer wanted $310 for the part. Locally here in SoCal, a non-OEM was $130 and an OEM from a parts dealer was $180. (Don't know how he would get OEM part for such a discount).

Total bill was $327.