I have a 2000 Buick Regal LSE. This problem used to be intermittent but has gotten to the point that I never see a "normal" operating state from my HVAC controller unit. The problem is that when I turn my car on the controller usually comes up completely blank except the 4 red lights on the passenger side climate control. The heater then comes on at high fan.
I took it to local Mechanic. He fixed a vacuum leak and it worked for 2 days. I took it back and he said that the HVAC controller was bad. So, I bought a refurb and installed it. It acted the same as the original... He suggested I take it to a GM dealer.
I took it to a GM shop and they pronounced the refurb unit bad... I asked them if the actuators/ vent doors were working and they indicated that they were-all that from a diagnostic test. So I replaced the control unit with one from a more reliable source and got the same erratic performance.
So, I might take it back to the GM shop, unless the forum has some ideas.
Voltage at the fuse for the HVAC unit is about 12. I can pull the fuse, replace it and sometimes the unit will reset and work for a minute or two.
Could it be the PCM or an actuator (which one?) Maybe the ignition switch?