1996 Bonneville Heating and Cooling

I had the serpintine belt replaced in my 1996 Bonneville, and every since then my heating and cooling isnt working properly. The blower works fine!..If the blower decides it doesnt want to blow heat it doesnt. The climate control readout blinks and it blows cool air. If it does decide to blow heat the climate control readout is fine. The 2 main electrical components have been changed. Nothing helped. Still just blows heat when it feels like it. It acts like there is a heater door sticking shut or something. Nobody came seem to find that to be a problem though? Any help would be appreciated. Thank You