July 17, 2018

TT #107 Residential Fridge Conversion: A New Approach (Part 2)

By: Rob Lowe

Featured Picture

Compressor ConversionThis is the second of two Technical Tips which provides 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 this article I’ll review the data generated and what we learned from it together with some helpful information for those that decide to go with this approach.

The Big Difference: An Absorption (RV) Cooling Unit to a Compressor Cooling Unit (Residential)
While at JC Refrigeration, I learned that an absorption fridge is designed to cool the fridge compartment first, then cool the freezer. Knowing this lends credibility to the often made comment about a traditional RV fridge: ”My ice cream won’t stay frozen, especially in hot weather”. A compressor equipped fridge cools the freezer area first, then cools the fridge compartment. This approach explains why the people often comment after a residential conversion: "Finally my ice cream is frozen - and my beer is cold.”

Some Adjustments after initial use:
Location of Thermistor & Sensor After the first week and in consultation with JR at JC Refrigeration, we agreed that moving the Black thermistor (that was located on the fourth fin from the right side near the top) to the middle fin in the middle of that fin would be a wise move so that it could accurately measure the internal fridge temperature (Yellow Arrow). I also learned how to put the fridge in the diagnostic mode so that I could see in the display, the actual temperature that the thermistor is reporting. To do this: press the Mode and Set Temp buttons together until 88 reads on the display, then press the Mode button to move the number reading up from 1 to 2 to 3. Release it there and the display will show the ‘Fin Temperature’. Repeating the pressing of the Mode and Temp buttons together returns the fridge to the normal control mode.

Use a Wireless Thermometer to Monitor:
Location of Freezer SensorInitially I set the Norcold Temp at 1, although I adjusted it to 2,3 and 4, (the higher the number, the longer the cooling unit will run to achieve a colder temperature). Installing an accurate wireless thermometer with a sensor in both the refrigerator and freezer (both shown inside the red ovals) made it easier to find a suitable location for both. It took a few days. There is always a compromise involved, since one does not want to move the sensor each time the fridge or freezer is accessed to get something out. The Norcold thermistor does not read the Freezer temperature, thus there is a tendency to ‘over cool’ the freezer to maintain the proper fridge interior temperature. The location of the wireless sensor also makes a difference, since there is no fan driving the air circulation. I decided to leave it on the rear of the shelf near the Norcold thermistor. There is always a difference between the ‘Fin’ temperature and the air nearby simply because of thermodynamics of the mediums transferring the ‘heat’ (air versus metal). Once the fridge runs for a while and we used items kept in the fridge, we could tell that they are as cool as they were ‘at home’ coming out of the residential refrigerator there. Using an Infrared Thermometer, I was able to locate the ‘Hot Spots’ in the fridge and found that the enclosed bin area was 4 to 5 degrees cooler than the wireless thermometer reported. This is great, since those bins store fruit, raw vegetables such as lettuce and luncheon meat and cheese. The Milk and Juice area was at the temperature reported on the wireless thermometer. The freezer sensor was located on the bottom of the freezer compartment that has the ice maker in it.

HourmeterAfter things stabilized for a few days I measured the current draw of the compressor (which was 0.88 Amps) and incorporated that information into an Excel Spreadsheet to monitor the fridge and freezer operation. The hour meter recorded the actual Compressor ‘On’ time and when compared to the time between readings, I was able to calculate the Percentage of ‘On’ time and  the actual amps drawn by the compressor over the timeframe. You will see that in the chart below.

The only power not reflected in the spreadsheet is the power consumed by the fans. The fans rarely run on most days, since it is obvious that there is a much better convection air flow with much less air flow obstruction than the former absorption cooling unit. Compared to the time those fans run now versus the time they ran when the absorption cooling unit was operating (on either gas or electric), I’m sure the power consumption from them is lower. In addition, there are only two fans in use now versus four with the old cooling unit.
Wireless ThermmeterOnce we installed the wireless thermometer sensors, we were able to record the freezer (top), fridge (middle) and ambient (bottom) temperatures (inside the coach) at the specific time that the hour meter was read and the time recorded. In addition, the minimum and maximum temperatures (inside the coach where the display is mounted) for the preceding 24 hours were recorded then the readings were cleared from memory. This is a simple button push to reset after taking the readings. A feature of this particular wireless thermometer is the trend of the temperature readings. A quick glance at the display for each area shows the direction the readings are trending. This is useful in deciding whether the Norcold temperature setting needs to be adjusted.    Variations are due to opening and closing the compartment doors (and leaving them open while items are put in or removed), and to a certain extend the effects of the changing ambient temperatures.    
Some Sample Data:
Sample Data
(Read each row across using the column titles as your guide to the contents below)

So, after a couple of summer trips and three weeks of actual use what are my conclusions? Would I recommend the conversion? The answer to the last question is a simple: Yes!

Given the ease of making the conversion, when all factors are considered, I’d highly recommend going this route to install a residential refrigerator provided that twelve (12) cubic feet of storage space is enough. After having the coach for almost eight (8) years we’ve adapted to the capacity and limitations and I can truly say it does not limit our enjoyment of this RV. Having a cold freshwater dispenser on the door of the fridge so that we don’t need to open the door to get a bottle of water, is very convenient. (Yes, we drink the water in our fresh water holding tank; we are cautious about where we source that water from.)

Given the location of our fridge at the front of the coach in a slideout, choices were limited for residential options. Neither of us were too concerned about the use of LP as a fuel, so that was not much of a factor, although the concern of a failed cooling unit and the potential for a fire did affect our decision. I know we would have selected an "Amish” conversion and that would likely have been a helium filled version.

Given that newer, high-end coaches are all electric, we think that when it comes time to sell, having a ‘Residential’ RV refrigerator will be a selling point. With our affinity for dry camping, energy efficiency was a factor in making the decision, although having four years of experience with a lithium battery system, we had confidence that power would not be an issue.  Ultimately the excellent service and care provided by JC Refrigeration, the owner JR and his family and staff in making the conversion in a timely fashion on a timetable that worked with our schedule was the ultimate confirmation of our decision. No emergency breakdown stress, no "how are we going to make the timing work”, no re-arranging schedules. Those benefits are worth a lot. Who knows how long the old existing unit would have continued to function? We all know that it was nearing the end of its useful life.

All in All – a good decision to convert our fridge to a truly RV residential refrigerator.  If you are facing a similar decision, check out this option. It is a viable alternative.  


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