heater controls

I have a 96 tahoe and I need seriuos help. Can anyone help me figure this out? I replaced my hvac controls twice and both times I did they smoked after an hour of being used. I also replaced the 2 actuators that conrtol the dampers and I still have the same problem. It only blows out to the floor. The deforst does not work at all. If anyone has any idea on what is going on with this problem could you please HELP!!!!!
Thanks Keith