I'm hoping someone can help me with this. I have spoken with at least a few companies, and they act like i'm the first person in the history of the world to have this issue.

I'm in Houston and every time it starts to get warm outside, my microwave gets filled with condensation from all the warm humid air dropping from the roof vent down into the microwave. This happened before, causing my microwave to arc and die. After buying a new microwave, I insulated the entire vent up to the roof, to keep air from condensing inside the vent itself, and leaking into the microwave, but I still had to run the microwave vent fan every morning to clear out all the humid air and dry out the inside of the microwave before using it, otherwise it would arc.

It's been a while since I've had to do that, with the weather we've had, but this morning I wasn't thinking, tried to start the microwave, and it immediately died on me. This is highly frustrating, so I'm trying to find a solution. I'm told there should be a damper on the vent on the roof, and my microwave also has a damper, but apparently not enough to keep the humid air out.

Any thoughts on a solution? I have to go buy a new microwave again, and want to make sure I install it along with some fix that stops this from happening again. My dryer also gets filled with hot humid air, causing me to have to run the dryer every day for 20 minutes, just to clear it out. Are my dampers for these vents just crappy?

I drew out how my microwave and vent are installed. It's literally a straight run up to the roof:

Yeah... the guy who did our roof said there was one. Unfortunately, I'm not able to get up there and I have to go through our roofer because it is a condo.

Honestly, I was thinking about just cutting the vent in the attic, and installing a fan that slowly spins, pushing the air out of the vent.