Step 1 test the fan motor.
How to test attic fan thermostat.
Locate the thermostat casing and open it using a screwdriver.
Switch off the power of the attic fan and remove the power cord.
Once done test that the motor still works by plugging the motor into an extension cord that is connected to an outlet.
If the fan turns on the motor is still good.
Note down the temperature settings for later reference.
Also note down the power rating and the fan capacity in cubic feet per minute.