Electronic Climate Control being strange

I have a Buick Riviera 1982 with a 307 Olds engine. It is equiped with electronic climate control. I've had it for 3 years and it's worked perfectly. Now however, it has started doing strange things.

It never gets the cabin to the selected temp, close, but never on it. The upper level vents blow cold air that changes speed with the fan, while there is hot air coming out of the foot warmer vents. At random times the system opens the bi-level doors blowing cool air in my face, but then quickly goes back to foot warmer doors.

It can't be the heater core because the air coming out the bottom is hot. There's 3 acutators, all seem to be functional. There's no blinking lights on the Control Dash. How would cold air bypass the temp door, and the mode door, and blow through the upper level vents? There shouldn't be any air going to the upper vents when the mode door is in foot warmer mode, correct? How do I check the mode door?