After the car is warned up grab hold of the two heater hoses if one is hot and the other cold, flush the core. If both are hot go inside and find out why the blend door is not working. And if you want the A/C fixed you need to do more then lift the hood.

Check your coolant level, sound's like your low on anti-freeze, that will cause your heater to blow cold.

Flish heater core

Yes

Lack of heat is 99.9% of the time: Low Coolant. Reservoir full? Any drips under the car?

Flush the heater core out in both directions several times.

I have a 91 firebird and there is no heat when I turn it on it blows out cold air what to do I need to get this fixed it's turning told where I live and having to drive to work in a cold car and with my ac it will blow a little air but it's not cold and I looked under the hood one day while the ac was on and the compressor was not even running