Wonky climate control - replace head unit first?

[moruzzi]

Have a 2002 w210 wagon that has been a great car. Looking at adding another w210 for college daughter when she is home and another commuter car.
Anyway, looked at a 2000 sedan with about 90k mi (about $4k asking) mostly very good condition. Someone replaced stock radio at some point but more important the climate control is screwed up.
Pixels out so you can't tell settings it temp, auto manual buttons don't reliably work and fan button does not reliably work and is sticky. So it seems like the head unit would need to be replaced first to even be able to get to the diag codes (need working pixels looks like one can be had on eBay for ~50-100$). Pressing cold arrows repeatedly does get cold air to come out, then it stops then starts again..., go to hot and can get hot air.
Anyway just trying to verify the module is the main control, replace that first, and then look for other issues with working diag codes.

Alternately just pass on this one and look for another.
Thanks
Paul