Microwave Exhaust Fan Not Working? How to Restore Airflow

When an over-the-range microwave exhaust fan is not working, the vent feels weak and steam and odors linger. Usually, clogged filters, a stuck damper, or a failed fan motor is the cause. First, check and clean the filters. Then, inspect the damper and fan motor below.

Safety first. Unplug the microwave before you open the cabinet. The high voltage capacitor can hold a lethal charge long after you unplug the unit, so it must be discharged before any internal work. Because of this shock hazard, leave the magnetron, high voltage diode, and capacitor to a qualified technician. Never run the microwave empty.

Parts to inspect for a microwave exhaust fan that is not working

1. Charcoal Filter

The charcoal filter cleans recirculated air on an over-the-range microwave that does not vent outside. When it clogs, the exhaust feels weak and odors linger. So pull the filter, usually behind the vent grille on top, and inspect it. Replace the charcoal filter on schedule, because it cannot be cleaned.

Unplug the microwave before you remove the filters.

2. Grease Filter

The grease filters sit under the microwave and trap grease from the cooktop below. When they clog, airflow drops and the fan struggles. Therefore, slide the filters out and check them. Wash metal grease filters in hot soapy water, and replace them if they are torn or crushed.

Unplug the microwave before you remove the filters.

3. Damper Assembly

The damper is the flap in the exhaust duct that opens to let air out and closes to stop backdrafts. When it sticks or breaks, exhaust airflow drops or outside air blows back in. So check that the damper swings freely and seals when off. Replace the damper assembly if it binds or no longer closes.

Unplug the microwave before you reach this part, and have the high voltage capacitor discharged first, since it can hold a lethal charge even when unplugged.

4. Fan Motor

The fan motor drives the exhaust blower that pulls air through the filters and out the vent. When it fails, the exhaust fan does not run or runs weak. Therefore, unplug the unit, reach the fan motor, and test it for continuity and free spin. Replace the fan motor if it is open, seized, or noisy.

Unplug the microwave before you reach this part, and have the high voltage capacitor discharged first, since it can hold a lethal charge even when unplugged.

Clean the filters first

Before you suspect the motor, clear the airflow. First, slide out the grease filters underneath and wash them, or replace them if crushed. Then, check the charcoal filter behind the top vent grille on a recirculating unit. Because clogged filters are the top reason for weak exhaust, this step often restores airflow with no parts.

Get the parts

We supply OEM and replacement parts in bulk. Browse the Appliance Parts catalog, or request a bulk quote for volume orders.

Is the microwave old or failing often? So weigh a repair against a new unit, and browse complete microwaves and more when a replacement makes more sense.

Most of the time, a microwave exhaust fan that is not working traces back to one worn part. So replace it, then run a short test with a cup of water and confirm the fix.