exhaust fan back flow - Montana Owners Club

Phil Eyler · 07-07-2014, 05:22 PM

I have a unique problem with my 2014 3402. When I turn on my exhaust fan while cooking on the stove top it blows my flame sideways. Yes, the flap is open and according to the techs they can't find anything out of alignment. They admit there is a problem but can't figure out what.They are going to contact Keystone. Anyone else ever experience this problem. I'm wondering if there is a missing gasket or something. I don't want to remove the microwave myself because the Monty is still under warranty. Any advice? Thanks

rohrmann · 07-07-2014, 05:43 PM

We have that happen on ours, but it seems to happen more when one of the ceiling vents is open or when the Fan-tastic Fan is running. There is air flow causing it, but have learned to ignore it.

maximo · 07-07-2014, 06:50 PM

We had the same problem with our 3580 Big Sky. They had to replace our Micro Wave / Convection Oven and they found a piece of sheet metal blocking the duct. Removed the obstruction and replaced the Convection oven and all was well.

Frank

**Carl n Susan** · 07-07-2014, 08:16 PM

I believe these microwaves are designed for household and RV use. Households don't have an exhaust port to the outside. The microwave come with a panel covering the RV exhaust port and it is not uncommon (like Frank's unit) to find they old world's craftsman at Montana forget to remove it.

WaltBennett · 07-08-2014, 01:14 AM

Ahh - Households usually DO have an exhaust vent to the outside, especially if the wall is an outer one. Over the range microwaves come with the option to mount them either way, but the installer is supposed to read the directions at least once & remove the piece of metal for installations that have a vent.

jcurtis934 · 07-08-2014, 04:07 AM

Ours also causes the flame to "suck" to the right and the tips of the flame will change to yellow when we operate the exhaust fan. Been that way since new and I haven't even thought about taking down the microwave to see why most of the suction is on the right vent underneath the microwave. John

davidaf · 07-08-2014, 06:50 AM

Our exhaust fan didn't have an issue but Keystone failed to mount the Microwave to the back wall. They couldn't get the bolt into into the mounting plate so they just left it hanging from the cupboard above. You can imagine what happened. Though it didn't fall all the way just about 2 inches luckily. Probably wouldn't hurt to pull it off the wall and make sure they did things right.

DAR · 07-08-2014, 04:52 PM

I think you could turn on the exhaust fan go outside the Monty and look to see if the flap is up or partially up to determine if they have removed the sheet metal that blocks the flow to the outside vent.

Phil P · 07-09-2014, 12:28 AM

Quote:

quote:Originally posted by Carl n Susan

I believe these microwaves are designed for household and RV use. Households don't have an exhaust port to the outside. The microwave come with a panel covering the RV exhaust port and it is not uncommon (like Frank's unit) to find they old world's craftsman at Montana forget to remove it.

Hi

My stick house has exhaust fans to the outside of the house both over the stove and in the bathroom.

Phil P

jfaberna · 07-09-2014, 01:11 AM

My 2014 3402 seems to have fan issues when we cook. The flames jump around and it blows back into your face. I'll look into it. I just thought it was a crappy design.

jcurtis934 · 07-09-2014, 04:12 AM

Yes, I did go outside to look at the vent flaps and they are open and working as normal. I just move the pan I'm using to the right on the burner to account for the heat being forced to the right. Call me lazy on this issue. Tried to convince the wife to do without the microwave so that I could install a real vent hood with enough power to suck your clothes off...but she wouldn't bite on that one. John

nosticks · 07-09-2014, 10:23 AM

You might want to try the bathroom fan blade swap with the vent hood blade. The blade just pops off each fan and pops back on. It will increase airflow and will be much quieter. If it doesn't solve the problem, you have all of three minutes invested and you can swap them back.

laburrows · 07-18-2014, 05:21 PM

Had the exact same problem with my microwave in my 2014 3100. Thought I was going crazy. RV tech in Pismo Beach California knew what the problem was right away, they had to take the microwave down and rotate the backdraft damper and realign it because it want opening up. Once they did this, the problem was fixed. Someone at the factory didn't install it correctly.

woodtic · 07-19-2014, 05:31 AM

There are two exhaust flaps on my rig. One is the plastic vent mounted to the outsideof the trailer. The other is a part of the micro/con oven. The original installation on mine had the external vent preventing the internal vent from opening more than 1/8 inch. I had to get up there and do a little trimming to the external vents plastic. Now my internal (metal) vent opens about 3/4 of an inch and it flows much more air. No more problems inside while running the fan.

I learned about this issue and the fix over a year ago here on the MOC. Hope thats all you need as well..

Irlpguy · 07-19-2014, 08:52 AM

As with woodtic one of the problems with our microwave fan was the metal flap part of the microwave. I removed that flap altogether and it made a huge difference, however on high speed the air being exhausted has to come from within the trailer and some will indeed pass over the flames and affect them.

You have not said what make or type your microwave is.

I have a Fridgedaire convection microwave and it uses a dual squirrel cage fan, it is two speed and by design can be mounted in the back of the microwave to either exhaust out the back or the top. QC being what it is with some of these folks it is possible it is mounted incorrectly. Ask me how I know this, the folks that replaced the control board and the fan on mine, were ready to remount the microwave when I noticed the fan was not in correctly, a rather red faced tech over that.

Good luck with your solution.

bikefever · 10-13-2015, 09:24 AM

I discussed the issue with back draft and poor suction with Keystone customer service during the 2015 Rally. They looked at it and said that they never heard of the issue. Got the Montana back without a fix.

Today spent further investigating the issue. On the outside vent cover there was a center piece that serves no purpose other than restricting the metal vent from opening. Removed this piece which helped but the metal vent was still only opening about an inch and still had poor suction and back flow. I bent back the two lower corners of the metal vent. The vent now opens to nearly 90 degrees. Suction and back flow issues are fixed.

kdeiss · 10-13-2015, 01:49 PM

Their should be a damper lock spring under the range hood.pull out to unlock in to lock the damper

kdeiss · 10-14-2015, 01:46 AM

[quote]Originally posted by kdeiss

Their should be a damper lock spring under the range hood.pull out to unlock in to lock the damper should be on the right side near the filter.

Ozz · 10-18-2015, 03:03 AM

Check these pictures out, I didn't know this extra internal flap was there..
I changed the fan to a more powerful, (CFM) fan and installed additional lighting.

https://goo.gl/photos/dqka2r6NPNjPApS87

ranch560 · 10-18-2015, 09:28 AM

It seems like every year there is a discussion about our microwave exhaust vent and flaps and there appears to be a huge mystery of how they work.

First of all, most microwave over the range units are residential and are typically built and made to same specs, especially the low end models RV manufacturers use. They can be vented through the top (usually this is how they leave the factory or they can be vented out the rear. Our Montana's require a rear vent. So now whomever installs the unit (amish craftsmen?) has to change the micro to rear venting. This requires minor changes including changing the flange and damper location from top to rear. It also requires removing the squirrel cage motor and turning it 180 degrees and reinstalling it. I do know about a SOB where this wasn't done. The result was air being blown throughout the inside of the micro and not the rear vent.

The rear metal flange and damper that comes with the micro must line up near perfectly with the exterior mounted plastic damper on the side of the Montana. And most of these plastic dampers have a mid support that blocks the micro metal damper from fully opening. This may cause added back pressure and the micro doesn't exhaust properly. Also there is typically a foam gasket that is part of the rear metal damper and attached flange.

I removed my metal damper as I feel only one damper (my exterior plastic) is required. Almost all residential installations have only one damper. The exterior plastic one is the important one as it keeps out insects.

As to removing a micro for an inspection, this typically can be done in 5 to 10 minutes. It consists of removing 3 large screws in the cabinet above the micro and gently lowering the unit while threading the electric cord out the hole. It rests on a grooved track at the bottom rear. It's a two person job as it is bulky and they weigh about 40 lbs.

As stated, if you are not sure about your damper opening up fully, turn the unit on high, go outside with a flashlight and do a visual.

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