Heater problems

[Dbanks12]

Have a 94 Park Avenue that has a electronic heater in it, replaced the alternator a week ago and now the car warms up fine, then the temperature numbers start flashing and it goes to cold by itself. Tried turning it off, turning the temp up and down and it stays on cold or heat on the drivers side and cold on the passenger side. I'm stumped, tried disconnecting the battery cable again and letting the computer reset itself but it still does it, any ideas would be appreciated..car has a new rad and thermostat in it as of two weeks ago, tons of heat when it works!!

[HotZ28]

I assume, when you you changed the alternator that you also disconnected the negative (-) battery cable first, but did you turn the A/C controller OFF first (with engine running) before disconnecting the battery cable? If not, the controller lost it's calibration and would need to be re-calibrated using a TechII scan tool. If you are patient, (and have a big coat & gloves) the system will usually reset on it's own after about 50 ignition cycles (engine starts with time delay for system to try re-calibration).