Replace Combo Oven - DONE!!

I posted last fall that our combo microwave/convention oven had died, and the new Sharp models do not fit the original trim plate.  After much searching I found a GE oven (Model JES1109RRSS), which has all the features of the Sharp R820JS, plus an Air Fry mode!!  Internal size is up, from 0.9 to 1.0 cu.ft., and power is up from 900 watts to 1050 watts.  Width of the GE is the same, the door height is 1/4" less and total depth is 3" less than the Sharp model.  The box depth is a bit more than 1" less, which required an easy adjustment fix for the original steel brace brackets on the trimplate. The "feet" of the new oven are shorter, which required a 1/2" plywood riser plate to be added on top of the existing mounting foot plates in the cabinet.  The only trimplate mod was to the bottom flange of the opening.  The new oven has a "popout" on the bottom, close to the door, which that flange on the trimplate bumped into.  Simple fix was to just carefully "roll" the back 1/4" edge of that flange downward so it fits.
I chose to also modify the cabinet to add a couple "muffin fans" which we had used extensively to cool rack-mounted electronic equipment back when I worked for Motorola.  They are not extremely high airflow, but are quiet, and have very good bearings, rated for 60,000 hours.  They ran 24/7 in the equipment we sold to the military.  I chose to do this because there isn't really any airflow around the Sharp oven, other than what seeps through the slots in the trimplate.  [[https://www.flickr.com/photos/201182969@N08/][/See photos here.]

Our original wardrobe cabinet above the passenger bunk was previously modified to be a pantry; that is where I installed the fans.  I used a 4 1/4" hole saw to cut the holes in the wall separating the oven cabinet from our pantry cabinet.  I felt the holesaw could splinter the wall as it went through, so I had prepped a set of wood plates for each hole, one plate on each side of the wall, with the corner holes matching those of the fans.  With those plates clamped tightly to the wall, the holesaw made a clean cut (but did create copius sawdust!)  Then removed the plates and installed the fans.  I added a surface mount switchbox from HD and wired the fans/switch to plug into the existing duplex outlet above the right side of the microwave.  We use the fans only when in convection oven mode, which is when it gets pretty hot in the oven cabinet.  Nuking a cup of coffee does not require using the fans.  When we use convection bake, we open the pantry door, the fans draw in air through there, around the oven and exhaust out through the slits in the trimplate (plus the added 1/4" space at top due to shorter face.)  And then we continue to run the fans until the oven cools down.

Those steel brackets attached to the trimplate connected to 4 existing screws in the back of the original Sharp oven.  Surprisingly, the GE oven has four existing screws in almost the same locations.  Because the GE oven box is 1 1/8" shorter than the Sharp, plus about an inch different in location, I used a 1" and a 1 1/2" corner bracket for each brace bracket, put together back-to back to relocate the attachment point.  Worked great.

NOTE:  if you've never done this... the oven is attached to the trimplate via those steel brackets, BEFORE the oven is installed.  You will realize this when you try to remove the trimplate, and discover the oven wants to come out with it!  Takes two to do the install, #1 to hold the oven/trimplate up while #2 gets the power cord situated and plugged into the outlet.  Then slide the oven into the hole.
We completed the install over Memorial Day weekend, and then did our 7 week "spring trip".  All aspects worked great, looks great.  DONE !!!

Thank you Rick for sharing this project with the PC community.  Though our original 2007 Sharp microwave continues to serve us well today, I have uploaded your post, just in case one day we need to replace it.
 

I have to ask you why you felt the need for extra ventilation with those fans?  Was your original Sharp microwave over-heating?  The front face-plate around the microwave is fully-vented.  Did you determine that to be insufficient?

Well, regarding the decision to add fans... there were several factors.

The original oven had worked fine for nearly 14 years, 2010 thru 2023.  I purchased this rv in 2016, so can't speak to it's first 6 years, but our vast majority use of the oven was as microwave.  Because that is such a short cooktime, the oven and cabinet don't really get hot.  We would mostly use convection mode for baking the refrigerated Pillsbury rolls, which only take about 10 minutes after preheat... again not too bad.

The oven died when we were baking a frozen casserole dinner, which specified to bake at 400 degrees for 60 minutes, after pre-heating.  High temp for a long time.  The cabinet was feeling hot at that time, and it appeared that the final failure mode was preceded by a failure of the thermostat and/or high temp limit switch... the casserole was charred, even though the cooktime was not completed, so the oven had gone into a full-on mode until the fusible links in the power supply melted.

There was online debate in my post last fall about how I could replace the fusible links in the power supply, but I felt "something else caused those to melt."  New fusible links won't fix the root cause.

So (1) I dumped the dead oven, keeping the trimplate with hopes I could reuse it, and started my search for a replacement oven.  The GE is a near perfect fit.  BTW, I got it at Best Buy in May, for $200.  Even if it has a shorter life, that's very economical compared to the cost of a Sharp.
Reason #2, when the oven is removed, it was a pretty easy project to install the muffin fans.  Yes, there are slots in the trimplate, but nothing really to push the hot air out of the cabinet.  Now the fans draw in cool air through the open pantry door, and "push" the hot air out the front.  That certainly can't hurt.

Reason #3... I already had the fans, leftover from a prior project!!

I mentioned in the post we keep the fans running after baking until the oven cools down.  This GE oven, if the door is ajar after baking, the display says HOT OVEN.  So we leave the door ajar and fans running until that display goes away.

Ah, I understand!

I ended up doing something similar with our main front TV utilizing a pair of computer style fans.  The TV ran quite warm being confined, wedged up high in that location.  I initially ran the fans at 12V but the noise was irritating so I added a POT to lower their speed to run them whisper quiet.  I also added a simple switch to turn them on and off as not to mess with the RPMs every time.  The TV operates so much cooler with the fans.

Our microwave has also stopped running after 10 minutes on high.  Not on convection.     Assumed it was overheating.    We usually don't run it that long.   Still the original Sharp from
2006.    Otherwise works fine.    Thanks for all the tips on converting if needed.
Jim