It controls the temperature via positioning of one of the air doors. At least that's how my 64 works. The core is "hot" all the time, but depending on the position of the air temp door makes the incoming cabin air hot or not. And as long as all the seals on everything are in good condition, it works quite well. I reconditioned my heater box shortly after I got the car and it will run your *** out with heat, or you'll never know it's there depending on where you have the temp knob pulled.