Ahhh.. now that you put it this way. I am pretty sure I know whats wrong with it. Tim (zzt231) had a problem exactly the same as yours about 2 months or so back?
Came down to a dodgy resistor pack of some sort. I'll try to get him to post a picture.
Actually it was James (Viper_Nipplex) who had the problem... My problem as always been fueling problems and still is
Supra6, Under the center console there is a thermostat thingy that controls the tempreture for the whole car (You can see it as it's a black thing with a fan and a pipe that goes from it to an opening just above the rear ashtray), if that is disconnected the car will blow hot air. Connect it up and start the car. After a while when the inside of the car is warm, Put the fan speed to "Auto" move it after a while the fan should slow down when you play with the thermostat slide thingy and adjust the temprature.
If it still plays up, PM me as I have a "spare thermo thingy plug under the console" laying around and we can try and test it with that or try and diagnoise the other problem... (faulty heater tap valve from a vaccum leak etc...)