Yes, have that problem and just gave up and now run the fan if the lights are on. Your temps are safe no matter what. Frankly Yeti, just let it run, the air exchange is more important than the temp. So long as the roots are above 50 and below 80 the plants should do fine.

I think I was told the fan needed full power to start and then it could be turned down, regardless it would not work if turned down on the speed reduction unit. Happy Ho HO