OK, this is weird, can you help me out? All my heater and A/C controls seem to function great. Ice cold A/C, HOT air heat, until I switch to defrost then it steadily cools of until just cold air blows... I turn to floor or vent and its HOT again??? Got so ticked off, I just took out and ordered a new heater core, but it seems if the heater core were bad, I wouldnt have great heat through vent and floor.

WHAt you think is going on here.

Oh ya, its a 95 F150 5.0 Auto 4x4

 

If you get heat ANYWHERE, it NOT the heater core! As was said in another thread, when selecting Defrost, the AC will turn on to make sure air going to the Windshield is Dehumidified. There is only one source of heat and air supply. All the rest is through vacuum controlled "blend" doors, that select either fresh air or air that has gone through the heater core.

Your problem has to be there somewhere.

 

There is a vacuum operated blend or diverter door in the airbox and it sounds like you may have a broker or cracked vacuum line. Does the cruise control work normally?