I think they call them “dampers”.

It appears there is a gap between the piping that goes up through the ceiling, and the piece coming out of the top of the microwave. That needs to be put together, and screwed and also taped with metal tape. I would assume that is what he is talking about, unless he was in the attic and saw it was venting into the attic and not out a vent to the roof.

@cat_ky Thank you! I hope you’re correct since no one will service microwaves. They say it’s cheaper to replace than repair, and id hate to replace it if it only needs a simple repair.

He does not say the microwave is in need of repair, he says the Vent Duct needs to be properly connected. See cat_ky above and ignore Jimmy.

Thanks for your responses! This is in my son‘s house so I can’t really check it out. Will convey info to him since he’s too busy moving into the house to surf houzz! Hoping for an easy fix.

The installation manual is available on the internet. I think the missing part is called a damper.

Post a better photo on here... maybe your son can text you a photo and you can post?

Totally frustrating! I forwarded responses to my son, hoping for an easy fix. Attached are his pics. I cannot see a gap in the venting. Any other ideas? Thanks!

You don't see the duct detached from the unit in the middle photo?

Thanks Jimmy. Saying it multiple times doesn't change fact that it is wrong. lol

Thanks, @Stax! Yup, I see it!

That is where it needs to be repaired at. Tell him to check his attic too, and make sure it is vented out the roof, so when it is repaired, it actually goes out where it is supposed to go.

Crazy, he is certain that is not a hole, just a reflection. He will try to hunt down the inspector to get the answer.

Thanks to all who posted helpful suggestions!

When I removed a vented over the stove microwave, I discovered pristine, like new vent duct. When the microwave was installed, whoever installed it didn't remove the baffle plate that would have allowed the fan to vent to the exterior.

So all of the expense and labor to install the venting was for nothing.

Mentioning this because it could well be the problem with your son's microwave.

Thanks so much, @ci_lantro! I thought of that too, and will certainly forward your comments to him.

Inspector now says that ductwork is fine, but unit was installed in recirculation mode!

@User Thats our plan! Lots of good video tutorials available. Plenty of house projects for now, so a vent hood will have to wait. Thanks for your response.

My GE installation manual called it a damper.

I googled the installation instructions for a Whirlpool; it was called a damper.

Ah, thanks, Jim. MW was existing to the house; I didn't have an instruction manual. Since the MW was getting tossed, I wouldn't have read it if I had one!

Damper/ Baffle--Whirlpool seems to recognize both terms.

https://www.whirlpoolparts.com/Shop-For-Parts/a6b5i1877/Whirlpool-Microwave-Air-Baffle-Parts

Flopsycat, another idjit installer like mine was!