Note: This ventilation idea was a failure. It is just too hot in the summers to adequately ventilate with outside air.
My broken thermistor wire problem on my trip this summer dramatically revealed the conditions behind the Isotherm refrigerator in my van. It was very hot back there. I used a towel rolled up to block the heat streaming in from it after I opened it up to try to fix it. I had put insulation all around the refrigerator leaving a hole above the compressor and behind the entire refrigerator open to the upper and lower vents. I assumed the compressor fan would be sufficient to draw air in and out. Crossing the Great Plains meant very hot conditions in the 90's to over 100F as well as uncomfortable humidity levels. Added to that was my westward trek meant the refrigerator side of the van had the sun beating down all day as well.
The original construction of the cavity in my van had a 3" deep shelf support in the back meant to provide a seal for the old propane refrigerator. I thought about removing it but didn't want to make a new support for the upper cabinet floor so I left it. There was a 3/4" gap between it and the compressor that I thought would be ok for the ventilation. It probably was not.
I wanted to improve the ventilation behind the refrigerator since I had it out anyway. I got pointed to a couple of guys who had addressed this issue thanks to Di. They were very nice in explaining the problem and their solution as described in this Yahoo Roadtrek post. You have to be a member to see it but I want to give credit where credit is due.
The problem with these fridges as installed into RVs is that they are made to work in boats where the ventilation goes from the cabin interior under the fridge base, up the back, drawn thru the compressor by the fan and out the top front of the fridge back into the boat cabin. RV's have vents in the back wall behind the fridge for the propane venting as propane emissions are highly toxic. The Roadtrek guy thinks the air tends to not get pulled adequately into the compressor or the hot exhaust air gets pushed back into the compressor by our cabinet configurations setting up a loop of hot exhaust over the compressor. This would hamper the cooling the fan is supposed to supply.
Their solution is to build a duct open at the bottom - going up to the compressor fan and sealed at the top which pulls it forward to make the fresh air go thru the compressor and out the top vent. The idea is to seal the top vent from the bottom vent with the only exit through the compressor. The compressor fan provides the positive air flow draft.
The remaining area behind the fridge outside of the duct can be insulated for additional performance enhancement of the refrigerator. The better the insulation around a refrigerator, the better it keeps the cold in.
The Roadtrek guy used hard foam insulation to make his duct. I decided to use Refletix foil bubble insulation to make my duct. I get a little insulation from it but mostly it provides some flexibility to fit the curvature of the van wall while still having enough stiffness to stay in place. Plus, I can flatten it to get the refrigerator through my narrow aisle. It is easier to handle than the stiff foam boards.
I'll describe how I did the project in a later post. The diagram below shows how the ducting should work with the Isotherm refrigerator.