Cooling Trend - RV Enthusiast Magazine

Cooling Trend

by | Apr 26, 2024 | Pending Approval

Photos by the author

When heat zaps the efficiency of an absorption refrigerator, adding strategically placed blower fans and a dose of fiberglass insulation can overcome high ambient temperatures — and make your ice cream frozen again.

RV technicians compile a vast amount of knowledge over the years, especially when it comes to absorption refrigerators. While the cooling concept remains the same, these refrigerators have evolved into safer appliances. I can remember when I started RVing in 1972 — you actually had to light a tube with several holes that would run all the way to the burner and heat up a Klixon valve to allow the gas to flow through the burner. Today, RV refrigerators have electronic controls, which should make them more efficient. But hold that thought for a moment.

Although absorption refrigerators have grown in size and capacity, they still utilize cooling units that require heat to move the hydrogen, ammonia and water solution up through the boiler into the condenser. One of the major drawbacks to using high temperatures to make the refrigerator/freezer cold is its operation in hot weather. High ambient temperatures allow the absorber coils to get really hot, which interferes with the separation of the hydrogen, ammonia and water before it goes into the storage tank. As the ammonia vapor tries to turn back into liquid, the temperature needs to be controlled. Efficiency really suffers when the ambient temperature rises well above 100-degrees F.

To combat any loss in cooling efficiency, refrigerator manufacturers have very specific installation instructions that allow heat to be removed from the back of the refrigerator. The heat extraction process is even more critical when the refrigerator is mounted in a slideout, because the traditional roof vent is replaced with a second wall vent. We all know that heat rises, so moving the heat out through a side vent is more restrictive since the heat has to take an unnatural pathway.

Over the years, I’ve learned that adding additional fans in strategic locations will make a world of difference when it comes to removing heat in compartments not configured for maximum ventilation. Also, a two-door refrigerator does not produce as much heat as its four-door cousins because there’s only one electric heating element as opposed to two in the bigger models — and the much larger cooling unit emits far more heat. Thus, adding fans to move the air more efficiently through the vents lowers the heat index, which results in colder temperatures in the refrigerator/freezer boxes.

blower fans, wire, two-pin connectors and cable ties
The parts for this project were assembled with blower fans purchased on Amazon along with wire, two-pin connectors and cable ties. Plan on spending around $100 for all these parts.
dual vent panels for accessing the area where the fans were installed
Since the refrigerator was installed in a slideout, it had dual vent panels for accessing the area where the fans were installed. This configuration is not as efficient as an installation with a top vent.
I recently helped out an owner of a two-year-old fifth wheel that has struggled with keeping food at safe temperatures in hot weather — and he hasn’t had frozen ice cream since owning this rig. His Norcold 1200 series absorption refrigerator was installed in a slideout room incorrectly and was poorly ventilated. One glaring problem was that the gap between the absorber coils and wall behind the refrigerator that was too large at around 3-4 inches. Ideally, the gap should only be about ½-inch or less to allow the air ventilation to travel up through the inside of the absorber coils — not over the outside of them.
Most of the four-door model gas/electric refrigerators are using one or two small cooling fans (sometimes three) mounted in the back of the cooling unit. Nice try, but they are oftentimes mounted in the wrong place to provide optimum heat removal. Most of the time they are mounted right above the absorber coils and too far down below the low temperature condenser cooling fins — essentially not doing much.

Another problem — in a slideout installation — is when the refrigerator is installed higher than the top vent, forcing the heat to go all the way to the ceiling and cavitate before “trying” to be forced out the vent. This is not efficient.

Yet another dilemma is the lack of a ramp between the ceiling and the top rear of the refrigerator, which when installed correctly prevents heat from collecting at the top of the refrigerator. It’s like putting an icebox in the sun. Realistically, the refrigerator should be removed and the compartment revamped to be more efficient, but that’s a big job — and in this case made even more difficult because of the kitchen island counter that was in the way.

The solution was to add stronger fans — and position them in such a way to move the heat out of the compartment, a process that I have been using for many years with great success.

Before the modification, the owner was running the refrigerator on the No. 9 position, which was the maximum. The refrigerator compartment was maintaining only 50 degrees F at the time (during three-digit summer temperatures), which was not a safe temperature for food. The freezer was struggling to keep food frozen. As the ambient temperature dropped, the box temperature when down a bit — but still not sufficient to maintain safe food for more than a day or so.

original fans
The original fans were small and inadequate. It’s one of two or three that are installed at the refrigerator factory. Unfortunately, they don’t push much air. We just left them alone when adding the new fans.
new fan mounted to the inside of the lower vent panel
The new fan mounted to the inside of the lower vent panel must be positioned so that it will push as much air to the rear of the refrigerator as possible.
The first thing we did was order four 12-volt DC blower fans from Amazon. (Search “UTUO Brushless Radial Blower Dual Ball Bearing High Speed 12V DC Centrifugal Fan with XH-2.5 Plug 120mm x 120mm by 32mm 4.72 x 4.72 x 1.26 inch). Each fan was $15.99. These are 12-volt DC fans that draw only 11.4 watts.

Finding the best locations for the fans took some experimentation over the years; I finally came up with a plan that was relatively simple to implement and the results have been fantastic. One fan is installed on the back side of each vent door (upper and lower) and two are mounted below the absorber coils, one higher than the other. In this configuration, the bottom fan in the vent panel was mounted so that it could pull air in from the outside and feed that air to the fans mounted below the absorber coils. The fan mounted in the upper door is positioned so that it pulls the air from the top of the compartment and blows it out through the vent opening. The original fans did very little and were left alone; they are controlled by a thermostatic disc at the evaporator near the boiler.

The placement of all the fans is critical — use caution to stay away from the right side of the refrigerator where the burner is located; this area can be extremely hot. The fan on the lower access door was mounted a little to the left of center so that it would blow towards the absorber coils, which were to the left of the insulated burner assembly. The two other blower fans were mounted below the absorber coils right in the middle of both absorber coil sections. The upper blower fan was mounted in the middle of the access door since would not be affected by the burner. We also installed a couple of two-pin connectors in the wiring to the fans in the vent doors so they could be released when opened.

All of the fans were mounted with cable ties; over period of time the heat will probably cause them to become brittle, but they can be replaced.

In order to get power to the fans, we simply tapped into the 12-volt DC wires going to the refrigerator. These fans don’t draw enough power to affect the function of the refrigerator; a 5-amp fuse was also installed in line. A switch was also installed behind the lower vent door to turn off the fans in cooler weather when they are not needed. It would be more convenient to have the switch inside, but that requires additional installation time as well as finding a practical path for the wiring. You should never drill holes in the refrigerator to route wires.

cable ties mounting the fans to the inside of the vent panels
closeup of cable ties
We used cable ties for mounting the fans to the inside of the vent panels. Holes were drilled through the fan housing and the vent panel. Be careful not to overtighten the cable ties — snug is good. Always use black cable ties or those designed for extreme service.
Air being funneled through the channel formed by the fan housing
Air is funneled through the channel formed by the fan housing, rather than the sides in typical muffin fans. This provides a stronger flow of air that can be directed properly in the back of the refrigerator.
The only caveat to this installation is fan noise. The blower fans we selected move much more air, so they are on the noisy side and may disturb close neighbors. You can opt for quieter fans, but they will not move as much air. The blower fans can be turned off at night as the weather cools down.

Another set of Beech Lane fans that we purchased were mounted to the evaporator fins inside the refrigerator. These fans can also be found on Amazon (search “Beech Lane 12V Refrigerator Evaporator Fin Fan”) and sell for $39.99. They attach quickly with alligator clips and are designed to circulate the air down the back of the refrigerator and to the top when the door is closed; they also reduce frost build-up. There are three fans in the plastic housing and together they pull only 1 watt and produce little noise (20db). The 12-volt DC power wire was routed down through the condensation drain tube to the outside and connected to a power lead. The ground lead was connected to the negative wire on the interior light, which was only a few inches away.

We then addressed the problem of the questionable installation of the refrigerator in the compartment. We are not able to remove the refrigerator, so we needed to come up with some way of stopping the heat from building up on the outside of the absorber coils. We were able to stuff R13-rated fiberglass insulation between the absorber coils and the outside wall, while taking care not to get it balled up and into the absorber coil gaps. The area only needs about 3-4 inches of insulation (in height).

The next part of insulation targeted the top of the refrigerator inside the compartment to prevent the heat from attacking the aluminum-foil covered Styrofoam on the refrigerator exterior, which affects the freezer compartment. The insulation only needs to come to the edge of the refrigerator. Ideally, if we removed the refrigerator, we would have made an angled ramp from the top of the refrigerator to the top of the access door. This was not possible because even with the vent door removed, there was not enough access to install such a ramp. The insulation was a good second choice.

This whole process can be repeated for a two-door refrigerator, but you will only need three blower fans (maybe only two) depending on the installation of the refrigerator.

The next day the owner of the fifth wheel excitedly reported that the temperature inside the refrigerator was down to 35 degrees F — and he once again had frozen ice cream. We know how important that is! Instead of running the refrigerator on the highest setting (No. 9), the lower temperatures were maintained while set on No. 4 — and even lower temperatures were achieved when the side of the fifth wheel was out of the sun. Not only does the food now stay safe, the owner will likely realize a saving in energy costs, especially when running on propane while parked off grid.

connectors being cut
short pigtail with a two-pin plug

We cut the connectors off the wire pigtails from the new fans mounted in the vent panels. These wires were then butt-connected to a short pigtail with a two-pin plug, which can be disconnected when the panels are removed for access down the road.

fish tape being sent down the upper vent
A fish tape was sent down the upper vent access to the lower vent access behind the refrigerator to capture the wires needed to connect power to the upper fan.
Two wires being taped to the end of the fish tape
Two wires being threaded carefully around the cooling unit obstructions
Two wires were taped to the end of the fish tape so they could be threaded carefully around the cooling unit obstructions and through the upper vent access.
wires being butt-connected to the two-pin plug leads for the top fan
Once the wires were captured through the upper access opening, they were butt-connected to the two-pin plug leads for the top fan.
two lower fans
The two lower fans that will direct air through the absorber coils were prepared for mounting in a location for best air flow. A short white cable tie was used to secure the wires, but black is better in this environment. (We ran out of smaller black cable ties, so we expect they will be replaced in the near future.)
arrow molded into the fan housing
An arrow molded into the fan housing shows the direction of the air. Make sure the fan is pointed in such a way to pass air through the absorber coils.
layer of fiberglass insulation
A layer of fiberglass insulation (not shown) was installed between the trailer wall and outside of the absorber coils to make sure all the air from the lower fans is directed properly. If the refrigerator is installed properly with the use of a spacer to close the gap between the wall and absorber coils (not the case here), this insulation will not be necessary. The bottom line: Air must go through the absorber coils.
power wires for the new fans being connected
The power wires for the new fans were connected to the refrigerator’s existing 12-volt DC power source.
toggle switch installed in a metal bracket behind the refrigerator
A toggle switch was installed in a metal bracket behind the refrigerator so that the fans can be turned off when not needed in colder weather. The cabinetry inside the fifth wheel made it too difficult to pull the wiring for the switch to be installed near the refrigerator. Never drill a hole in the refrigerator to route wiring.
the wiring in the back of the refrigerator being connected
the wiring and two-pin connectors clear of any obstructions
All the wiring in the back of the refrigerator was connected and secured with cable ties. Make sure the wiring and two-pin connectors are clear of any obstructions and exposure from any high-temperature areas. These fans pull very low wattage, so light gauge wire will do the trick.
triple-fan device made by Beech Lane
A triple-fan device made by Beech Lane was installed on the interior fins to circulate cold air throughout the refrigerator to improve efficiency. These fans are one of many on the Internet; this model installs using simple alligator clips. The positive wire was run through the refrigerator drain tube and connected to an independent 12-volt DC source; the negative wire was connected to the interior light ground. The negative wire might also need to be routed through the drain tube in some refrigerator models.
fiberglass insulation between at the top of the refrigerator and cabinet
We needed to add fiberglass insulation between at the top of the refrigerator and cabinet because there was no “ramp” to aid in removal of hot air through the vent. The fiberglass will suffice, but in a perfect world, the refrigerator should be removed to install a heat deflector.
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