Pontiac Repair: Heater issue 1994 Firebird (chkd the usual), pontiac firebird formula, pontiac firebird

Question
Apologies if this has been answered already.I have a 1994 pontiac firebird formula. Heater doesnt work first thing I thought was maybe heater core was bypassed by previous owner and that wasnt the case i changed the thermostat and it still would not blow heat. Then i found that if i switch it to just the face vents it will blow heat but as soon as i change it to defrost or feet it blows cold air. I am not familiar with this and im tired of wiping fog off my windows manualy...help!. Can someone point me in the right direction. Thanks in advance!

Answer
Hi Shawn:

I'm a bit perplexed here. Changing the mode on the HVAC control head shouldn't change the way the temp blows other than defrost would be colder then heat/vent setting due to the fact the a/c will run if it's warm enough outside. I'm thinking you have an issue with the tempature door or tempature door actuator. It may be stuck in a mid point and it just takes a while for the heat to build up due to the door being stuck midway between cold and hot. does this evnetually have good heat after it ran a while? If that were the case I would suspect possably a restricted heater core. after the car had run for say 5-10 minutes see if you have a noticable difference in the hose temp between the inlet and outlet of the heater core. if there is a big difference the core is restricted if they have about the same temp thata is not the issue here. I'm still stuck on why it makes a difference in the mode selection though?? Good luck :)