This is the third of what was planned to be two Technical Tips which provide a viable option to converting an RV refrigerator from an absorption to a ‘residential’ refrigerator. In the first article, I presented the background, decision process and the actual physical conversion procedure. In the second article, l reviewed the data generated and what was learned from it, together with some helpful information for those that decide to go with this approach. As with any change there is a learning curve and this article will include some further information that will assist those who retain an absorption refrigerator and want to make it work more efficiently. In addition, adding the following improvements to the compressor equipped, newly converted refrigerator will add value.
One of the drawbacks to an absorption refrigerator is the fact that it is designed as a static, ice box that relies on heat being withdrawn from the insulated interior. Other than convection there is no air movement from the cooler to warmer areas inside. Therein lies a potential drawback. When the doors are open, warm, humid air is drawn in and it tends to deposit water vapor on the cooling fins which develop into ice and frost. The air does not quickly circulate as it would when it is fan forced as in a residential compressor refrigerator.
As with many improvements found in RVs, necessity is the mother of invention and a well designed, low current draw, easy to install fan system has been introduced by RV Cooling Unit Warehouse which is a 15” Triple Fan RV Frost Guard unit, available on Amazon. It is strategically attached to the cooling fins inside the refrigerator to move air across the fins, improving air flow and cooling throughout the refrigerator, while reducing frost build up on the fins. It has three small fans, two are on when the first switch is activated and the third is switched on by a separate switch. This improvement mimics the fan cooling in a residential fridge balancing the interior temperature while reducing frost build up. This improvement works on any cooling source (the original absorption or the compressor driven conversion). Without boring you with temperature readings taken in various areas of the refrigerator, I can assure you that the temperature is better balanced. The blue LED back light can be independently controlled, although it provides no added value other than light. Prior to the conversion, I had replaced the original incandescent light fixture in our refrigerator with a flat LED array and covered the wiring with aluminum tape which is shown in the photo.
With improved air circulation, I began to think it would be a simple enhancement to add a self defrosting feature. I knew that on a residential refrigerator, there is defroster timer that typically turns off the cooling unit for about an hour while an internal defrost heater is turned on to melt the ice built up. This takes place out of view behind the interior panels of the refrigerator.
On the Norcold (or Dometic) refrigerators, the added fan system is powered from the coach battery, independent of the fridge controls. These fans operate whether the compressor (powered by 120 VAC) is on or not. If the compressor is turned off regularly, then the internal fridge temperature will rise slightly, allowing the ice and frost to melt. The resultant water would flow into the tray below the exposed fins and into the small collection bucket in the exterior access compartment. I asked myself "What would happen if the compressor was put on a timer and turned off for a couple of hours overnight, each night?” Would the frost or ice buildup on the fins melt? I had to try this since while installing the fan system, with both fridge doors open, I had seen melting of the frost and ice during the 30 minutes it took to complete the installation and run the wiring. With the doors shut I knew it would take longer. I tried turning the compressor off for one hour which started the defrosting process however two hours seemed to be better. Everything in the freezer stayed frozen so that was not a concern during the defrosting process.
To allow a timer to be installed on our coach, I had to move the Inverter powered plug (labelled ICE) away from its position tight against the exterior coach wall. This move made it possible to plug both the fridge and icemaker into the two receptacles on opposite sides of the timer and to view the timer easier. Cords were coiled up in such a way that if the timer needed to be removed to program everything could be removed to the access area as a unit.
I purchased a digital timer designed to control lights and appliances (Harbor Freight Chicago Electric Part No. 95205, UPC 92363 95205). It includes a back up battery to retain the time and programming during periods when the coach is in storage and not powered. It can be programmed with up to 8 ON/OFF cycles on a daily or weekly basis. I programmed it using military (24 hour) time, (which is easier to read given the location of the timer in the outer fridge access area), rather than trying to discern the small AM or PM. I set it to turn ON at 0:00 (midnight) and OFF at 1:00(AM) on program one, then back ON at 3:00(AM) and OFF at 23:50 (11:50 PM) on program 2. The 10 minutes of off time recognized that the compressor could be running when this program turns off the unit and gives a 10-minute period where it would be off before entering the 0:00 ON period. This protects the compressor from damage. The remaining programs were not used.