Fan coming on unexpectedly

Have you had trouble with the cooktop lights recently? The circuits for both lights and fan can be affected if so.

Does it happen when you are not cooking on the stovetop?

Your product support page is here, where you can get the owner's manual, installation instructions, parts list, etc. You can order Whirlpool parts from the Pros here.

If your controller needs repair, I do that. Details here.

Does this happen while you are cooking on the range burners under the control panel?? These type microwaves have a heat sensor built into them in the area of the control panel bottom. If the microwave control gets too hot from cooking on the stove below it the heat sensor will turn the fan on to keep the control panel from getting heat damage. The fan should go off after everything cools off.

You probably have a bad fan thermostat. This thermostat is supposed to turn on the vent fan if the microwave oven gets too hot (caused by cooking too much or having too many burners turned on on the range beneath the microwave oven). It should shut off in about 15 minutes after your turn off the range burners. But if it comes on for no reason, or won't turn off, then You probably have a bad fan thermostat.

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This moisture can accumulate from certain types of cooking (lots of boiling) in the microwave or in extreme cases, from a blocked grease filter or exhaust vent duct.

Spills or large amounts of accumulated moisture should be wiped off. Minor amounts can dry out by themselves easier if you leave the door open after cooking.

Also, when boiling on the stovetop, you should always use the hood vent exhuast fan to keep steam and grease out of the controls and the door area of the microwave. I always recommend using the vent fan with any cooking on the stovetop.

As long as it is not rusting the metal mesh screen or other parts of the door, it can be allowed to dry out over a period of days with the door open.

If it is a convection microwave, using the convection heat will help it dry.

There is a wire mesh filter and a carbon filter on the under side of the unit. IF they are plugged then it wont draw air. The other issue is this unit has a dual option for installing the fan. One is to vent to the outside and the other is to vent to the inside, if the fan is not installed for the correct usage, you have no airflow either.

I think a bad connection in a lucar styl plug is the problem.
Check all of the connectors that come from the switch/control pannel and the magnetron's transformer.
Make certain that it is not still charged up at a lot of voltage in the capacitor is lethal!!!!

NOT THAT I'M AWARE OF . YOUR UNIT SHOULD HAVE A SWITCH TO TURN ON AND MUST BE TURNED ON MANUALLY

Right, that would be MCO10UW and the owner's manual is here.

The owner's manual does say this, of course,

"To prevent overheating from taking place, the exhaust
fan is designed to automatically turn on at a low speed if
excessive temperatures occur. Should this happen, the
fan cannot be manually turned off, but it will
automatically turn off when the internal parts have
cooled. The fan may stay on for up to an hour after the
range and microwave oven controls have been turned
off."

That;'s standard on microwaves.

But these models do have a separate internal cooling fan (which should run any time you microwave) plus the hood vent exhaust fan, which should only run when you select it, or if there is an excessive stovetop or under-hood temperature.

So if it comes on whenever you microwave, that is incorrect.

When that happens, it's usually a defective vent thermal switch (a.k.a. hood TCO).

But since it's brand new, I would certainly contact Magic Chef about this. If it's in need of repair, they will fix it free, assuming the oven wasn't physically damaged.

For more help from Magic Chef / Ewave see here or their contact page.

For Magic Chef in Canada call 866.587.2002

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The fan pulls from the range top and either out those vents on top unless there is a vent in your upper cupboard. Then it is vented outside. Hope this helps.

Are any other bulbs in the home going out prematurely? If so, I would check the actual voltage of your power outlets. If not, the bulbs may be getting grease or debris on them from stovetop cooking. This can cause hot psots and premature failure. I recommend wiping them clean with alcohol on a cloth before installing them. I recommend that folks always have their hood fan on when cooking on the stovetop. Also, you might check with a local home center (Lowe's, Home Depot, etc.) to see if they have some high-quality (non-Chinese) substitutes.