Cooling Trend

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.

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.

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.

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.

I’ve seen many air-conditioners over the years where the condenser fins were completely mangled or flattened to one side, which will reduce efficiency. Straightening the fins can be painstaking, but a commercial tool for this application may speed up the process. You can also use a simple butter knife or similar tool that’s not too sharp to straighten bent fins. Once everything looks okay, reinstall the shroud and move to the inside of the RV to clean the evaporator.

The return-air filter is removed from the access panel and washed in the sink with soap and water. Make sure it is dry before reinstalling to prevent moisture gathering in the evaporator. In dusty areas, or when the air-conditioner is run most days, this filter should be cleaned at least once a week. Remove the filter from the return-air access panel so it can be washed with soap and water in the sink.

Newer formulations such as Nu-Calgon’s Evap Foam No Rinse Evaporator Coil Cleaner are self-rinsing; if you use an older formulation, be sure to rinse it thoroughly (all residue is gone) with a spray bottle filled with water. The water and cleaner will exit through the drain and down the side or back of the RV.

Next, you will need compressed air. Look up into the plenum cavity and you’ll see the fan; it may or may not be covered in dirt and dust. Don safety glasses and blow the compressed air on the “squirrel cage” or fan, dislodging any dust and/or debris. (A buildup here can actually cause the fan to be out of balance.) Inspect all the wiring, which includes the 120-volt AC Romex wires, thermostat and/or furnace control wires and the temperature sensors. Make sure that everything is intact; now would be a good time to clean up the wiring, if necessary, using cable ties or other restraining method. In many cases, builders leave everything loosely hanging around up in there.

Inspect the ducting inlet if you have ceiling-mounted registers and make sure that the separator — the piece of material between the plenum and the return air — is intact. If the separator is not sealed, cold air will be sucked right into the return air making the A/C far less efficient. In any case, as the air-conditioner ages, it’s probably going to be a little less efficient. You might think about upgrading the system with an RV Airflow kit that can improve efficiency by 30% to 40% (see “Rapid Cooling” in the April 2023 issue of RV Enthusiast — magazine). It’s fairly easy to install and a big benefit is a sizable decrease in noise. The kit directs the air through the plenum directly into the ducting, eliminating cavitating and swirling inside of a cavity.

A Few Final Thoughts
Another key to efficiency is to make sure that all the ducted ceiling registers are open. Closing off several of them will put pressure back into the plenum, causing more cavitation of the air that’s forced into the ducting. If you need to close some of the ceiling registers for one reason or another, you can open the air dump at the bottom of the ADB (if so equipped) slightly to alleviate some of the pressure.

Because the air-conditioner is a sealed unit, the freon is not replaceable; there’s no port to install the freon nor do these units use a receiver dryer, which is necessary for recharging. Over the years, I’ve talked to air-conditioner technicians who have installed a port in their system and recharged it — only to find out it’s leaked again.

All air-conditioners have a start- and run-capacitor and most modern air-conditioners have a control board. Any diagnosing and/or repair of the electrical system should only be done by a qualified technician. That said, staying on top of maintenance that can be accomplished by owners will yield big benefits — and keep the sweat away in hot weather.

If the no-rinse foam is not handy, you can use Coil King Condenser Coil cleaner, which is available at home improvement stores. Clean water must be sprayed onto the evaporator or condenser to rinse off this liquid product. It must be allowed to dry before running the air-conditioner.