Dash Temperature Control: Hot or Cold, no inbetween

Harvard wrote:
The cockpit control sends an analog signal to the flapper valve control module. If this module (forward of the firewall) has ever been subjected to moisture (as in condensation etc) it will corrode and fail to operate the flapper valve correctly.

Thanks Harvard. I thought that might be the first thing to check. Any ideas what that module might be called? (I tried searching Google for it, but nothing came up. The Winnebago parts system requires an old Windows computer to use...ugh.)