all speeds used to work awesome, then slowly "high" has become less and less reliable to turn on. now it wont at all. low is fine, med is fine, high not a thing.

thoughts?

sorry if this is a silly question.
hope its an easy fix, i miss my defrost :/

 

Perhaps the part of the relay that controls the high setting has failed. The fan runs on a different circut when in other settings to lower the speed, but high is just straight power without any kind of adjustment. Check your relays and perhaps do a test swap on the one that actuates the fan.

just my $.02