My heater fan works on medium speed and vibrates heavily on high speed. Does not work at all on low speed. Replace fan motor or resistor??

 

The vibration is probably because it is out of balance. Look and see what's up. Broken or bent squirl cage or debris. The loss of the lower speeds is most likely the resister but I think you might need to check the switch too? See if any how to videos out there. Good luck and Please follow up with your fix.