I have a '79 Bronco and a few days ago my heater fan decided that it only wants to blow at low speed. I can swith the switch to the high setting and the air flow doesn't change. I've tried it in all the heater settings (defrost, heat, hi/low, a/c, etc) and it behaves the same in all settings? Can it be as easy as a fuse or something or am I looking at replaceing the entire heater switch assembly in the dash? Obviously I'm hoping for something easy and cheap, but seeing as it's single digit temps in Michigan right now, I'll do whatever it takes to get some more hot air flowing! By the way, it does get hot air, I just can't move it around very well.

Thanks for any help you can give me.

 

Odd the you would have only the "low" setting. Usually the only one that ends up working is "high" since its the only setting that doesn't pass the electricity through a resistor to reduce the voltage to the motor. However, you might still check into the resistor module. Its gonna be buried in the dashboard somewhere near the heater controls. Not 100% certain as to where, my book only goes back to 1980.

 

Used to put a lot of blower swiches in 78-79s and sometimes vac control switch in them -both are in the heat -ac control head on dash- check with a test light.Poss blower resister(test with test light,mounted on blower case - 2 in. by 3 in apprx.- might be easiest to test first) though as 79 regulates power to blower for diff speeds with a 100% ground there all the time, and later Broncos use ground side switching for regulating speeds, and has bat voltage to blower motor all the time when the key is on- bad resister on these , only high speed present.