I have a 2003 Century Buick with 60,000 miles. After my car warms up and I turn the switch for heat cold air comes out. Sometimes it will blow hot and revert to cold. AC light is on all the time regardless of calling for heat or AC. What could be the problem. Thanks

The temperature blend door is not functioning correctly. The blend door is probably vacuum actuated, and a vacuum leak or disconnected hose could be the problem. Also, a physical obstruction of some sort might be preventing the door from moving. the fact that it goes from cold to hot and back makes me think vacuum leak.

MC may be right, but I think you also have a short in your AC switch, or maybe wires, if the light is on all the time.

Do you have it set to defrost?

when driving the car after its all warmed up, put the controls where you usually have them for heat. if they are acting weird, pull over (where safe to do so) and shut off the car. DONT touch ANY buttons on the heat cool panel. NONE… wait for about a minute then restart the car and drive. does the heat come back on and stay? if this makes the heat stay constant, then the ac system blend valve (which controls the flow of hot water to the heater core inside the car is messed up.

if this doesn’t change anything then i suspect the problem is with the electric side of things, (since the AC light is on)

Not to ask a dumb question, but; how long has the AC light been on all the time? what was done when that started? any under hood repairs related (timewise?) have you had any work done on the AC / Heat system? (ever?)