90°C is quite hot for a chamber temp, and beyond the 80°C max specified in the stock configuration.
I can understand “just setting the chamber so hot the fan its effectively disabled”, because the exhaust_fan is so loud But is 90°C really what your filament material wants? I admit my experience with high temp filaments is limited.
You may be interested in the exhaust_fan modifications I just posted in Quiet Exhaust Fan with Propotional Control!