Sometimes cleaning out your fan and or adding some oil is all it takes to correct a problem.
How to repair attic fan.
Most fans have an on off switch that bypasses the fan s thermostat.
This attic fan motor is the most expensive repair for attic exhaust fans.
If the fan comes on you have an electrical problem in the circuit the attic fan is on.
Have you had an roofing siding or insulation work done before you noticed the difference in performance.
A screw or bolt may have come loose.
It s best to hire an electrician to deal with electrical problems.
Your belt might have deteriorated to the point where it is slipping and not turning the blade effectively.
After you realize that it s not an electrical or thermostat problem the chances of it being a problem with the motor are quite high.
If however the fan still doesn t turn on the problem is most likely with the fan motor or the thermostat.