Gary RV_Wizard
Site Team
RV fridges made in the last 20 years claim to be fairly tolerant of being off-level and generally are spec'ed to allow up to 3 degrees side-to-side and 6 degrees front to back. That's from the perspective of the fridge, which is normally sideways in the RV, so it's 3 degrees tilt fore & aft in the RV.
Recently, though, I've been helping Paul Unmac test his invention, a device called the ARP that will control the heater (boiler) in an RV absorption fridge in a much narrower range than the factory control board. Paul believes this will extend the life of an RV fridge as well as preventing fires in failed cooling units. One of the test beds is a skeleton Dometic 6 cubic foot fridge set in a portable frame that can be carried around (for demos) and tilted in any direction at will. With an ARP installed and its optional data collection package connected, we can watch how the boiler reacts when the cooling unit is tilted.
The results amazed me! Merely tipping the fridge a few degrees to one side (by sliding a 1.5" board under one edge), the boiler temperature immediately soared! And I do mean soared - it climbed over 100 degrees F, in less than two minutes and showed no signs at all of stopping. We quickly re-leveled the cooling unit to avoid damage - Paul didn't want to risk the unit he is using for demonstrations at RV shows this fall and winter - and the temperature began to fall again nearly as quickly. I'm sorry I failed to get a picture of the display graph as the temperature climbed, but I was literally too amazed to click the shutter!
We've been telling folks that their fridge is OK if they can walk around comfortable, but now I'm not so sure. According to Paul's research, high boiler temperatures cause the internal rust inhibitor (sodium chromate) to crystallize and lose it rust preventive qualities. Loss of the sodium chromate increases allows the extremely corrosive ammonia to attack the steel tubing and eventually cause a leak. And a leak is both a failed cooling unit and a fire risk. Without extensive laboratory testing I can't say how much is lost, how quickly, and how much temperature rise is needed to cause it, but I think there is sufficient cause for concern.
Another thing I have learned by having the ARP data collection package installed on my own coach is that the boiler temperature can swing widely while driving. Mine actually was getting about 25 degrees (F.) cooler while underway at interstate speeds, and that causes the temperature in the fridge to rise (which I have observed), I can also see the boiler temperature move quickly when I pull into a rest area, slow down in traffic, or stop at the campground office to check in. The changes are immediate and dramatic. Paul says that climbing a highway grade also causes wide swings, sometimes hundreds of degrees. I surmise that wind is blowing down from the roof vent while driving ay highway speeds and that cools the whole process off. I have since added insulation around my boiler area but haven't been out on the road to see if it helps stabilize the temperature.
Paul has also measured temperatures on fridges installed in slide-outs and found then running substantially hotter than non-slide fridges. Slide-mounted fridges have the upper vent in the side and do not provide as much air flow over the coils as roof-mounted vents. He recommends adding a good sized fan at the bottom of those fridges to improve cooling unit performance as well as extending its life.
There is more information on the ARP controller and absorption fridge characteristics on Paul's web site, https://sites.google.com/site/arprvsafer/
I have no financial interest in this product but I did receive a free controller and data collection package in exchange for my help in testing it.
Recently, though, I've been helping Paul Unmac test his invention, a device called the ARP that will control the heater (boiler) in an RV absorption fridge in a much narrower range than the factory control board. Paul believes this will extend the life of an RV fridge as well as preventing fires in failed cooling units. One of the test beds is a skeleton Dometic 6 cubic foot fridge set in a portable frame that can be carried around (for demos) and tilted in any direction at will. With an ARP installed and its optional data collection package connected, we can watch how the boiler reacts when the cooling unit is tilted.
The results amazed me! Merely tipping the fridge a few degrees to one side (by sliding a 1.5" board under one edge), the boiler temperature immediately soared! And I do mean soared - it climbed over 100 degrees F, in less than two minutes and showed no signs at all of stopping. We quickly re-leveled the cooling unit to avoid damage - Paul didn't want to risk the unit he is using for demonstrations at RV shows this fall and winter - and the temperature began to fall again nearly as quickly. I'm sorry I failed to get a picture of the display graph as the temperature climbed, but I was literally too amazed to click the shutter!
We've been telling folks that their fridge is OK if they can walk around comfortable, but now I'm not so sure. According to Paul's research, high boiler temperatures cause the internal rust inhibitor (sodium chromate) to crystallize and lose it rust preventive qualities. Loss of the sodium chromate increases allows the extremely corrosive ammonia to attack the steel tubing and eventually cause a leak. And a leak is both a failed cooling unit and a fire risk. Without extensive laboratory testing I can't say how much is lost, how quickly, and how much temperature rise is needed to cause it, but I think there is sufficient cause for concern.
Another thing I have learned by having the ARP data collection package installed on my own coach is that the boiler temperature can swing widely while driving. Mine actually was getting about 25 degrees (F.) cooler while underway at interstate speeds, and that causes the temperature in the fridge to rise (which I have observed), I can also see the boiler temperature move quickly when I pull into a rest area, slow down in traffic, or stop at the campground office to check in. The changes are immediate and dramatic. Paul says that climbing a highway grade also causes wide swings, sometimes hundreds of degrees. I surmise that wind is blowing down from the roof vent while driving ay highway speeds and that cools the whole process off. I have since added insulation around my boiler area but haven't been out on the road to see if it helps stabilize the temperature.
Paul has also measured temperatures on fridges installed in slide-outs and found then running substantially hotter than non-slide fridges. Slide-mounted fridges have the upper vent in the side and do not provide as much air flow over the coils as roof-mounted vents. He recommends adding a good sized fan at the bottom of those fridges to improve cooling unit performance as well as extending its life.
There is more information on the ARP controller and absorption fridge characteristics on Paul's web site, https://sites.google.com/site/arprvsafer/
I have no financial interest in this product but I did receive a free controller and data collection package in exchange for my help in testing it.
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