1. Exhaust blower fan will not turn on. Click on the link for related article below
Cause 1: Bad Thermostat/Thermal Switch
In the microwave, there is a thermostat/thermal switch that turns on the exhaust fan when the air temperature rises to certain point and turns it off when the air temperature drops. If defective, it may stuck in on one position and either not turn on the fan motor or not turn off the motor, meaning keep it running. When it is not turning on the exhaust fan, use a millimeter to test the thermostat for continuity. If it is not have continuity, then replace the thermostat.
Search for the right replacement part in thermostat category.
Cause 2: Bad Relay Switch on Main Control Board
The main control board might be defective. However, this is not usually the case. Before replacing the control board, first check the exhaust fan motor and wiring. If the exhaust fan motor is not getting power, the main control board might be at fault.
Cause 4: Bad Exhaust Fan Motor
To determine if the fan motor is defective, remove the fan motor from the microwave and try turning the fan blades by hand. If the blades do not turn freely, replace the fan motor. If the fan blades do turn freely, use a multimeter to test the motor for incoming power and for continuity. If the motor has power but wonâ€™t run, replace it. If the motor does not have continuity, replace it.
Cause 4: Bad Low Voltage Capacitor.
The low voltage capacitor in the microwave feeds the exhaust fan. If it is defective, it will stop accumulate enough charge to properly feed the fan motor.
Use the millimeter, to test the LV Capacitor for the right capacity required for the exhaust fan motor.
2. Exhaust fan will not turn off. Click on the link for related article below
The reason is the thermal switch is triggered or stuck. Sometime in may turn on by it if the temperature near the microwave is high so your microwave wants to help you by turning the vent motor on.
From heavy use of the surface burner on the cooktop, the microwaves thermostat may sense to much heat and turn on the exhaust fan to cool down the internal heat
It cannot be turned off manually but it will turn off by itself after temperature drops to normal Typically take 10 to 20 minutes.
If the near or internal temperature is low and exhaust fan stays on longer then 20 minutes, then the thermal switch may be stuck/welded in on position and will not reset by itself. Solution is to replace the thermal switch that controls the exhaust vent fan/motor.
3. Exhaust fan makes loud humming noise. Click on the link for related article below
Most of over the range/oven microwaves are equipped with exhaust fan aka vent blower motor. When the bearings worn out, it will start emitting loud humming noise. The solution is to replace the entire exhaust fan assembly or the motor or replace the bearings. The last option is more time consuming and it might not be a success. But before order the replacement fan assembly, you need to make sure that the noise is coming from the exhaust fan. Turn off the exhaust fan and see if the sounds continue.
You can distinguish this noise from others by turning the exhaust fan off and listening to see if the sound continues. If it stops, the motor on the exhaust fan is probably the cause of the humming. This sound usually does not require attention, but if it continues to grow louder when you operate the fan, you may want to call a repair company.
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