1996 626 - cold air suddenly goes to hot (vent and AC both)
 

My 1996 626 suddenly developed a new problem with the air, both with AC on and with just vent (no AC). There does not appear to be a pattern on when it happens, but it happens more frequently with the AC on than with it off.

With the temperature slider all the way left, on maximum cool, the air will periodically just switch to heat. Just suddenly it will be blowing hot air. Moving the slider to heat and back to cool fixes fixes it immediately. But it will go back to blowing hot air anywhere from a few seconds to a few minutes later. Moving the temp slider back and forth always fixed the problem for a bit.

Any ideas?

Edit: It's a 5 speed (if it matters!)

You have a 1992 and a 1996 626 in your post. They are completely different cars so we need to know which one it is. Sorry, but there is a huge difference in the systems.

Oh dangit, I apologize. '96 626 LX

It uses an electric actuator to open/close the temp door. It could be a stripped gear in the actuator or it could be the heater control unit telling it to change to heat. The actuators come apart easily to check for stripped gears.

Replacing the heater control unit appears to have fixed the problem. Thanks.