I was driving my car last night and tried turning my heater on but it was just blowing out cold air. I had it set to "vent" on as hot as it could go and had it turned up like 3/4 of the way which in the summer usually will have my car ridicuosly hoty in 2 seconfsd. But alli was getting was cold air. anybody know what could have happened since my heater was working properly and hot as hell earlier that day and today the heater still wont work. Anybody know whats up?

 

What year is your car? Starting in 1987 GM started installing a diverter valve in the heater hoses to shut off coolant to the heater core when the A/C was on. Its possible it may be stuck in the "off" position.

You may want to also remove the passenger side lower dash hush panel and check if the cable is moving on the bottom of the heater box when you move the temperature lever.

 

it is an 89 GTA