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We have a built-in microwave installed above our gas stove. It is vented out through the back wall and up to the roof (not straight up, so I have cabinet space above it), and was installed this way by the builder. Since installation three years ago, when it is cold the microwave gets very cold inside -- I could use it as a mini-fridge. No problem with this, however, the cold air seems to also affect the internal exhaust fan. When it's cold, the fan does not come on when you start the microwave, so steam builds up inside. After a couple of minutes, the fan will come on; however, if running it longer I get an error code F7 (this started recently) which I can't find anywhere in the instructions -- its a Whirlpool Gold Accuwave model.
I don't know why cold air is getting in the microwave, but I think if I can stop that, all should be well. Other than this, it operates great. No problems during warmer weather--I don't feel warm air in it at all. Any ideas? Thanks!
You need to add a flapper damper in the duct to the outside. The one in the microwave is too low to be effective at preventing cold air coming down. When it gets to the fan, the cold is making the lubricant (if any) sluggish and causing the bearings to resist the motor turning. Eventually, the motor heats enough to make the bearings work and the fan starts rotating.
Most of these ducts are simple plywood or metal boxes that eventually lead to a pipe going through the roof. A flapper damper is a lightweight rectangle of metal that fits within the vertical duct, is hinged on one side, and has a lip around the base of it to prevent it from falling downward or that cold air to leak around the edges when it is closed.
Hmmmm I wrote a couple answers but kept erasing them. Each answer does not make sense based on your complaint. I never heard of a damper up at the roof vent. At the top of the micro there is one but it's for another purpose. When you buy a new micro there is a damper flapper in it's own mechanism. On top of that is a fixed cover held with one screw. You leave this in place if you have no external vent and you remove it if you do have an external vent. Outside wall vents I have seen dampers but not roof vents.
How the hell is it getting cold inside? I'm not clear on it's location. Is the micro on an exterior wall? Did the installer punch a hole in that wall to run the vent outside? They may not have replaced the insulation when they punched that hole.
I gotta tell ya. 3 decades and perhaps 5000 microwaves installed and I have never heard of a problem such as you describe.
"Is the micro on an exterior wall? Did the installer punch a hole in that wall to run the vent outside?"
Re-reading, and noting that the vent DIDN'T go through the cabinet above, I think you have it right. It looks like either there is a vent on the side of the house, or the vent goes between studs where insulation would normally be.
I don't put much stock in the flappers that are part of the unit. We had a similar cold air problem - not anywhere near as bad, but annoying. When I replaced that unit I noted that spray foam insulation that had been used as an air seal around the base of the vent stack. The foam had expanded enough after installation that the seal was slightly compromised, and a little air could leak in, especially when the fireplace was drawing a good draft and putting the house into negative pressure.
Hmmmm I wrote a couple answers but kept erasing them. Each answer does not make sense based on your complaint. I never heard of a damper up at the roof vent. At the top of the micro there is one but it's for another purpose. When you buy a new micro there is a damper flapper in it's own mechanism. On top of that is a fixed cover held with one screw. You leave this in place if you have no external vent and you remove it if you do have an external vent. Outside wall vents I have seen dampers but not roof vents.
How the hell is it getting cold inside? I'm not clear on it's location. Is the micro on an exterior wall? Did the installer punch a hole in that wall to run the vent outside? They may not have replaced the insulation when they punched that hole.
I gotta tell ya. 3 decades and perhaps 5000 microwaves installed and I have never heard of a problem such as you describe.
Nope, not located on an exterior wall, in fact our bedroom is opposite, and we insulated that wall for noise. They went into the wall and up, not directly above as is done with most over-the-stove venting; as I said I have normal cabinet space above (which I like), not the usual boxed in vent. Of course, I don't know why they did it that way--I'm not sure they do either. I wouldn't be surprised if it was the first microwave they ever installed above a stove--it wouldn't be the first "first" we've encountered with this home! I don't even want to talk about the Rinnai!
I'm glad I can give someone of your experience a run for your money. I wish I could figure out the problem,too. What's on the roof is a dome-like structure, but I don't know it's assembly. Perhaps there is some type of "butterfly" flap that is stuck. It won't be the easiest thing to check due to the roof line. But cold air is coming in and hasn't been a real problem until recently when I began getting a "F7" error code on the display. Otherwise, I have been really pleased with the unit. I'm certain my problem is an installation issue and not specifically with the unit.
I have never heard of venting a microwave to the outside. We have an over-the-stove microwave and the vent is on the top front of the microwave and blows air right into the kitchen.
All of the combo Micro/Hoods I've installed had the option of recirculation into the room through a filter or exhausting to the outside... either straight out the back wall with a damper or vertically with a damper...
Sounds like the damper isn't installed or stuck open... do you feel a draft of cold air at the screen? How about when the central furnace is on... it could actually be strong enough to pull in outside air via the hood ducting.
I was in a home once that had a nice fire going in the fire place... someone turned on the range hood over an indoor gas grill and I watched the flames get sucked out of the fireplace...
All of the combo Micro/Hoods I've installed had the option of recirculation into the room through a filter or exhausting to the outside... either straight out the back wall with a damper or vertically with a damper...
Sounds like the damper isn't installed or stuck open... do you feel a draft of cold air at the screen? How about when the central furnace is on... it could actually be strong enough to pull in outside air via the hood ducting.
I was in a home once that had a nice fire going in the fire place... someone turned on the range hood over an indoor gas grill and I watched the flames get sucked out of the fireplace...
This stumps me based on the info we have. But ya know what? That is an idea there. If the home is so air tight, then when the furnace is on and that return duct is sucking air in and the only place it can come from is the microwave, that could cause it to be cold. Simply the vent hood on the roof will not allow that much cold into the micro. Some negative pressure can force it in though.
That error F7 thing sounds like the micro has an electronic problem.
I have the very same problem. My original over-the range microwave vented through a previous venting system which was for one of those old double oven stoves. I have no problem. My new microwave was installed the same way and I get cold air coming in through the mesh filters as well as freezing in my microwave. However, it seems to happen most when it is extremely cold outside and windy. Other days, when the sun is out and no wind, there doesn't seem to be that problem. Can anyone tell me what's going on? The microwave has a damper on the unit, but that seems to be running okay. Did the original oven venting system (called a Braun) vent to the roof and was there possibly a damper in that vent that occasionaly gets stuck or something. I am a 68 eyar old woman with absoletely no knowledge of anything mechanical and even less educated about taking care of a home on my own.
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