Hi Dave,
Usually if the programmer looses it's "logic" a simple shut off the car for a minute and then a restart cures that issue. We used to have a write up about that in our collection of TSB's over at the netreg site in the maintenance section.
I'm thinking check for a clogged heater core or a bad motor and or linkage to the mixing door. Stupid question, I mean no offense; but did the heat ever work? The heater hoses are connected properly & not by-passing the core connections? The T-stat is okay? If it gets stuck open you get very little heat, ask me how I know!
Tom