November 9, 2018

TT #108 Residential Fridge Conversion: A New Approach (Part 3)

By: Rob Lowe

Featured Picture

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.

Fan Assembly

Improving the Air Flow:

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drawbacks to an absorption refrigerator is the fact that it is designed as a static, ice box that relies on heat being withdrawn from the insulated interior.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.  

Adding Self Defrosting:

TimerWith 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.

AC Plug RelocatedTo 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 Timer Installedthe 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.


Installation Notes:

The fan installation is quite a straightforward procedure. It comes with two side-mount brackets that are marked left and right. They are attached, in the location determined by centering the fan assembly on the fins, with Velcro® strips (included). Simply cleaning the mounting location with alcohol and holding the brackets into location using the guide tabs that are part of the brackets is all that is required. When they are secure, the fan assembly is pressed onto plastic tabs on the brackets until they lock in place. This fan unit is angled to force air over the fins, in addition to circulating air throughout the refrigerator area.
Compression InsertThe white power wiring is fed into the drain tube. On our fridge, the drain tray had to be removed to access the tubing which meant that the shelf retaining strips on each sidewall near the door Compression Insert Part Number needed to be removed. With the strips off, the upper shelf could be removed giving space to remove the drip tray. Our tray was securely stuck onto the drain hose and when pulled outward, the integral plastic nipple that fit into the hose broke off. After looking at alternatives to reconnect the hose, a trip to the hardware store to purchase a 3/8” (0.95cm) Compression Insert provided the hose connection point. The existing hole was drilled out so that the insert could be placed in the hole and the lower lip was bent to allow the insert to lay flush to the floor of the tray. A bead of caulking was used to seal and secure it in place. Once dry, the white wire was fished through the tray, out the insert and into the hose. It was pulled through the exterior end of the hose ready for connecting. The drip tray was reinstalled, with the compression insert pressed into the hose, then the removed shelf was reinserted into its track and the retaining strips were reinstalled. The exterior wiring entailed crimping the included piggyback connector onto the red wire, attaching the fridge power wire to this connector and inserting it onto the board connector. A supplied ring connector was crimped onto the black wire, then it was attached to a suitable metal ground.

Exterior Catch Tray Modification:

Catch Tray Fitting The Norcold refrigerator depends on the hose from the fin drip tray to deposit water into an exterior catch tray. With the absorption system the hope was that the water would evaporate Catch Tray installed naturally from the heat generated in the absorption process. With the compressor conversion there is the potential for more frost/ice buildup to occur and a proportionately larger amount of water to be drained into the exterior catch tray. Combine that with the compressor’s much cooler operation and water can fill the tray and overflow onto the floor of the exterior compartment. The solution is to provide an exterior drain that allows some water to collect in the tray, with the overflow being directed to the exterior out the access door. A friend and fellow RVer just completed such a modification and with his permission I have incorporated his photos into this TechTip. 
This first photo shows the drain tray removed and a coax feedthrough bushing being inserted in a newly drilled hole about halfway up the side of the catch tray. A similar feedthrough is shown in the lower right side of the photo. (Yellow Arrows) (The compression insert I used in the drain tray repair could also be used). A clear vinyl hose is attached to the reinstalled catch tray as shown in the photo. The end of that hose is directed out the fridge access door where excess water will fall to the ground. The conversion, with these upgrades, is a very cost effective, safe, energy efficient refrigerator that will perform well in an RV environment.Drain Tube





Thanks for your comment.It will be published after reviewing it.