Common Repair Issues with Microwave Exhaust Fans

Paradise Appliance
April 9, 2020
Microwave Repair

Microwaves that are mounted above the counter are often placed over the stove. For this reason, many microwaves have an exhaust fan feature that takes the place of the oven hood fan where the microwave has been placed. The microwave exhaust fan is designed to pull heat and cooking fumes up away from the stove and channel them outside the house. This function is essential for clearing smoke, keeping the kitchen a comfortable temperature, and controlling powerful cooking aromas. So when your microwave exhaust fan stops working, it’s time to roll up your sleeves and investigate. There is no one reason why microwave exhaust fans stop working. There is a collection of possible causes and you’ll need to hunt down which one is keeping your exhaust fan from spinning. Let’s start at causes that are easiest to identify and fix then work our way down the list.  

Dirty Grease Filter

The grease filter is the first filter that cooking-fumes go through in the exhaust fan assembly. The grease filter does exactly what it says: it is a metal filter designed to catch grease out of the air as it rises above the stove. The grease filter is a reusable part that becomes slimy with grease very quickly with a normal degree of household cooking. It is difficult to scrub but easy to soak.

The grease filter is the metal grate on the bottom of your microwave, directly over the stove. Make a habit of taking it down and soaking it in a sink of hot water and detergent. Then run it through the dishwasher. It can be made good as new many times over. 

Clogged Charcoal Filter

When the microwave blows the oven air back out, it does so through a charcoal filter. This is the final stage of recycled air filtration. It removes odors, food particles, and other lingering elements of cooking fumes before expelling the filtered air up through the oven hood or back into the kitchen.

However, charcoal filters get clogged full over time and they are not so easily washed and reused. You’ll need to stock up on a few charcoal filters and change yours at least once a year. The charcoal filter is located behind the exhaust air outlet grill. In some models, this is easy to remove to replace the charcoal filter and in some, you may need to unmount the microwave and remove the case. 

Malfunctioning Touchpad

There’s also a chance that everything about the fan is fine but the button that is meant to activate it. For all modern microwaves, this means the touchpad. Touchpads are pressure-sensitive buttons that actually have the button depression mechanic underneath the plastic membrane. However, if even one touchpad button has stopped working, you’ll need to replace the whole touchpad to enact a repair.

Other than the effort to be electrically safe with your microwave, a touchpad replacement isn’t as challenging as you’d think. It is a front panel connected with wire leads. Replace the panel, switch out the wire leads, and your fan might start working again with a working touch button. 

Damaged Damper Assembly

The damper assembly is a special kind of air valve for the exhaust fan. It ensures that air only passes through the exhaust when the exhaust is on. If the damper assembly stops working, so too may your exhaust fan. The damper assembly is inside the fan and is specifically a flap that prevents outside air from entering the exhaust system. The flap can be metal or plastic and is often spring-loaded.

Open the assembly to determine if a spring has broken or a piece has jammed. It’s also possible that the plate itself will be cracked. 

Broken Fan Motor

Of course, the simplest assumption when the exhaust fan stops working is that the fan motor is broken.  While this isn’t the easiest problem to fix, it is a direct problem to solution. You can test whether the fan motor is broken by trying to free-spin the fan blades with the cover off. To be sure, use a multimeter and careful connection to the wire contacts. If the multimeter can send and receive a signal, the fan motor is working. If no current can flow through, the fan motor is broken.

If you can confirm with a multimeter that the fan motor is not broken, you’ll need to disassemble the microwave to replace the fan motor. Replacing the fan motor is an electrical repair that should be done carefully with the microwave unplugged and discharged. 

Faulty Control Board

Underneath the touchpad is the control board. This is actually the brain of your microwave and determines all the signals it manages and all the functions featured by the microwave. If the control board is faulty, it may not be sending the signal to start the fan even if the button and the fam assembly are all in working order. The control board is one of the last things you want to replace because it is also the most delicate and integral part of the microwave. You’ll want to test the control board with the multi-meter before pulling out and replacing your control board. 

Repairing Your Microwave Exhaust Fan

As you can see, there are many different systems that come together to make every part of your microwave work. The exhaust fan relies on the fan assembly, the damper assembly, the touchpad, and the control board. If the filters get clogged or any part along the functional path stops working, your exhaust fan may stop turning on or off. In some cases, malfunctions can even result in your fan turning on but never turning off.

If you’re looking to repair your microwave exhaust fan beyond changing the filters, be prepared to be very cautious about electrical shocks. Microwaves contain a high voltage capacitor that can retain a dangerous electric charge even when the microwave is unplugged. Either proceed with extreme caution or take the safe route and hire a professional to diagnose and repair your microwave. Contact us today to schedule an inspection and repair of your microwave.


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