I have replaced my ac/ heat fan resistor a couple times now and not sure what keeps blowing it.it will Blow 1,2,3,4 but I can only us 5. Then fan goods when I replace it. It not working hard at all and it will work on heat or ac but the all of a sudden it craps out. Not sure what I’m missing please help and ty

 

Maybe too much physical resistance in the blower fan motor. We just had our 2005 Yukon in to our local mechanic, and he said that about ours, and replaced BOTH, so issues since in 2 months.

 

Check the plug that connects to the resistor for good tight connection. A loose connection can cause problems as well as a motor.

 

Might be crap plugging up in the motor where on low speeds the motor isn't getting cooling air, that will cause over heat problem.

 

Just because the fan spins, it doesn't mean it's healthy. Dry bushings, worn or dirty commutator bars or brushes will all cause the motor to overload the resistors.