My 93 C4 convertible has a problem with HVAC controls. After a really hard driving rain about two months ago, the controller for my HVAC stopped working. No functions what so ever so I bought a unit off Ebay and replaced it. Same results, none of thefunctions work at all. A few days later I started the car, it (the original unit) worked on the way to work and hasn't worked since. I also checked all of the fuses in the compartment on the right side of the dash. Ideas?
Thanks in advance.

 

I would think that isolating the (ground) connection for that HVAC controller and hooking it up to a known solid ground connection as a "test" might be helpful. It would at least eliminate a "grounding" problem as your trouble source.