Cold air from outside coming in house through vent

some microwaves vent to the exterior. check outside for a vent. If it is a recirculating model, perhaps the filters are plugged, the vent pathway is blocked (packaging material) or a loose panel at the back so that the exhaust fan air is leaking out somewhere else. I don't know what else it could be unless the fan is loose on the motor shaft and the fan motor is running but the fan blades are not moving air.

check your through the wall vent .that is connected to your microwave.this leads to the outside of your home.While outside,look to see what type of cover is used.your hardware person should be more able to help you with this.

Interesting post, because I have the same problem! I have spent the better part of today researching and taking our microwave apart (partially) to inspect the top portion re: outside vent. Everytime the microwave is on, the "active vent door" (manufacturer's term, not mine!) opens. Apparently this is normal. But it also opens when you turn on the vent fan, when cooking on the stovetop. I don't like this feature, because I think it 'overrides' the outside venting system. I double checked our outside vent to ensure that when this oven was installed, the person did in fact allow the flap to be open when the fan is on (he did). So I think what 'our' problem is, is that the microwave active vent sort of interferes with the outside vent, thus more of the cooking smell being blown into the house instead of the outdoors. I was thinking of simply disconnecting the gizmo that make the active vent door open each time you use the oven and/or vent fan option however I don't think that's a good idea as apparently the main purpose of the active vent door is to keep the electronics of the microwave oven from overheating. The more I read about this version of microwave, the less impressed I am with it. Lots of electronic issues with it. I am not fussy either with having the microwave over the cooktop. Sorry I don't have a solution for your problem but I do feel your pain!!!

Check to see if the damper is stuck, either on the exterior vent outside the house or at the microwave. Also, did the blower get turned to point at the desired exaust direction. Unfortunately, both interior possibilities will require removing the microwave.

The inspector is correct, air should be coming through the top louvers, although you sometimes will have a little air coming from the sides and back. Drop the microwave and see which way the blower is rotated, towards the louvers or towards the back or top. Some units also have a panel that blocks the venting from going the wrong way. Good Luck, Appliance Specialists

As long as the air flow is good, gravity shouldn't make any real difference.

For more free DIY and other help & advice, feel free to contact me.

William E. Miller, AS-EET
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Microwave Oven Control Panel Repair Nationwide
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you should never cover any vents, they are there for a reason, to keep you safe from fumes, damp, etc.. (If talking about vents that are outside you home). If you are talking about appliance vents then you run the risk of them breaking if you cover the vents, due to overheating

Vents that are outside the home including boiler vents etc... exhume all of the carbon dioxide that is bad for you. Vents that are there to stop damp, if blocked may cause you to have a problem with damp in the future.

If this microwave has vented outside in the past then most likely a bird or something has built i nest in or on the vent blocking airflow. If its always been this way then in order for this model to vent though an exterior duct the blower motor has to be flipped so that it blows upwards and a vent connector needs to be installed. This is a fairly easy process once the microwave has been taken down but can be dangerous because there is a capacitor that holds 4000 volts that can discharge though the cabinet if you're not careful.

The installation manual should help you deal with these issues. If you don't have yours, you can download it here:

http://shared.whirlpoolcorp.com/assets/pdfs/literature/8101P641-60.PDF
OR
http://shared.whirlpoolcorp.com/assets/pdfs/literature/8101P710-60-R1.PDF

As a bonus, you can also get your owner's manual here;
http://shared.whirlpoolcorp.com/assets/pdfs/literature/8112P268-60B.PDF

One important thing is to make sure you have a good vent door on the outside of the home. If that's not working right, it allows mor cold air in. Also, the pipe should be insulated.

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