1996 S10 overheating, no heat blowing inside cab?

Thermostat is getting stuck. It is really cheap and easy if you know about cars. As far as the heater core, it could also get clogged up, As for the defrost only working, that has to do with a door that is supposed to open and close. It could be in the control switch in your dash, which is electronic or runs off of a vacuum that could be cracked anywhere in the dash, or if the door that directs the heat and air conditioning is disfunctional, then you are looking at possibly taking the whole dash out to fix that. I know my Monte Carlo did that and that is what they told me and it was expensive, so I just let it go. Oh, I forgot, you could have air pockets in your cooling system. Your cooling system has to be bled sort of like your brakes do. If it is not thermostat, I would ask someone to bleed the system, it only takes one wrench and there are 2 bleeders. You start engine until fan kicks on which means water pump is circulating and then loosen the bleeder, which one I am not sure where to tell you on this vehicle. But anyways, unloosen it until water starts sputtering out and keep it open until it is a stead stream with no air bubbles. Then go to the other bleeder and do the same thing. Actually this really makes sense that you hear bubbles in the heater core because that may be when the air is pushed into there. Yeah, I didn't believe the person that told me about this but it is true a mechanic showed me. You have to bleed the coolant systems. Good luck.