The ultimate perfomance test for the RV absorption refrigerator occurs when ambient temperatures are very high. Absorption refrigerators are silent, can withstand the rigors of highway travel and use far less energy to transfer heat than compressor-type units, but, unlike the latter, they are limited to about a 50- to 60-degree difference between outside and inside temperatures.
Here, we will give you some tips that can help improve efficiency and examine some of the reasons why refrigerator compartment temperatures can get unacceptably high. We will briefly explain the absorption theory, the three requirements for proper operation, how to perform some preventive-maintenance inspections and how to troubleshoot the LP-gas system and electrical components.
In order to get the best performance, start the refrigertor operations several hours before a trip, and do this with it empty. Pre-cool all food that is to be transferred to the RV. Similarly, frozen food should be frozen prior to its transfer. If possible, purchase cold food for refrigerator storage. Wipe condensation, if any, from whatever food will be placed in the RV fridge. Refrain from lining the shelves with aluminum foil, which will restrict airflow. Also, try not to leave the door open any longer than is absolutely necessary.
Current models aren't as sensitive to leveling as older models, though. For example, Norcold maximum off-level limits for the refrigerator itself are 6 degrees front-to-rear and 3 degrees side-to-side. If you can, park the RV with the refrigerator side vent in the shaded area to avoid the heat of afternoon sun. When very hot weather is expected, place some refreezable blue ice-type containers in the freezer overnight, and then place them in the upper part of the refrigerator compartment during the hot part of the day. This will slow down the temperature gain and may keep the food cold all day. Also, in hot weather use 120-volt shore power if it's available, instead of propane.
All RVers, especially full-timers, should make it a regular practice to defrost the refrigerator. Excessive frost buildup on the evaporator fins will inhibit the proper heat transfer.
Before you start troubleshooting, you need to understand the theory behind the appliance. The cooling unit consists of pipes that contain the refrigerant mixture of ammonia, water, hydrogn, and sodium chromate, an anticorrosive chemical. A heat source from either the LP-gas burner or an electric heating element is necessary for circulation of the refrigerant through the tubing. Similar to a coffee percolator, the ammonia and water boil and rise up the pump tube where the water separates and returns to the boiler. Since ammonia does not condense as quickly as water, this gas continues to rise to the condenser where it expels its heat. Next, the ammonia gas returns to a liquid state and trickles down through the low-temperature evaporator located in the freezer compartment. This is where the hydrogen and pure ammonia meet. Here, the evaporation process is greatest and the majority of the heat is removed. Remember, cold is simply the absence of heat. Due to quick evaporation, the liquid ammonia becomes a gas again and circulates to a high-temperature evaporator located in the refrigerator section where more heat is absorbed from the food items stored there. This gas then flows by gravity through a pipe to recombine with the water to begin the process again, which is why sufficient leveling is to be observed. Because the "absorbed" heat must also be eliminated, one of the most important elements for successful refrigerator performance is adequate ventilation.
Most coaches have a side vent and a roof vent that must be inspected in order to maximize heat dissipation, which is more critical in high ambient temperatures. We should note here that any inspection and cleaning of the vents should take place only after the refrigerator has been turned off for several hours.
The roof vent should be removed, if possible. It's usually secured with screws, or the cap is held down to the base assembly with metal clips. (Note: Some newer models have nonremovable top vents.) This will let you view the opening and the condenser. It's not uncommon to find bird nests, leaves and other debris in this area. For those of you who store your unit for extended periods of time, this inspection is very important. Fires have occurred in coaches when the refrigerator was turned on if there was combustible debris on top of the burner exhaust that had lodged in this area over time. Also look for insulation that has fallen down in the flue area.
After removing all the larger particles, you should be able to see the side vent opening as you look down through the roof cavity. At this time, you can blow out the smaller particles, dirt and debris using compressed air with the side vent either removed or propped open if it is hinged. The side vent is louvered, and there should be no screen or filter material or anything else attached to the inside of this assembly that would obstruct airflow.
Make sure that the louvers are open and not smashed down. This is critical because they serve as the intake air supply for the refrigerator. In order for a draft to be created to expel the heat upward through the roof vent, the temperature of this air must be lower than that which exists in the back of the refrigerator. Greater differences in these temperatures will increase the amount of draft.
In a coach I used several years ago, I installed a battery-powered fan, which was mounted on the wood platform at the left rear of the refrigerator, and i experienced a documented improvement of 5 to 8 degrees in the refrigerator section. I would only turn this fan on in ambient temperatures higher than 90 degrees F. Believe me, there is a significant difference between 42 degrees and 50! Nicro Solar (2065 W. Avenue 140th Street, San Leandro, California 94577) offers a similar solar-powered fan that functions similarly without battery drain.
Also, the interior light is DC and will have a 400- to 800-milliamp draw to power the control, the interior light and the "climate-control," or high-humidity operation function. This feature can help in high humidity ambient temperature operation because it heats the metal frame around the front of the refrigerator to help prevent condensation from developing. During extended periods of storage, turn this switch off along with the interior light to prevent parasitic drains to the battery.
Other ways to maximize hot weather performance include checking the door gasket for proper sealing. Insert a dollar bill around all four corners of the door frame and gasket. When you pull on the bill, there should be some resistance all the way around, indicating the seal is acceptable. Also, make sure the interior light shuts off when you close the door. This added heat will create higher refrigerator temperatures and battery drain.
The following procedures should be performed by qualified repair technicians, but are provided to allow the owner to understand what is done. Begin by first turning the manual gas-control knob to the OFF postion. After the roof vent has been removed, the flame spreader or flue spiral baffle can be removed. It is attached to a wire and hooked to the top of the exhaust vent. The burner shoudl either be removed or covered with cloth before you clean the flue. A flue brush can be used for this cleaning, such as a shotgun bore brush. Run the brush tip up and down through the flue to remove rust and soot. The flame spreader can also be cleaned and should be reinstalled at this time, along with the roof vent.
Additional LP-gas components can be accessed through the side vent: the burner assembly, the orifice and the thermocouple or electrode assembly. Be sure to follow the manufacturer's instructions. The burner and orifice can be removed and cleaned with compressed air and denatured alcohol. Do not use a wire or drill to clean the orifice. In newer electronic-ignition designs, the electrode assembly can be carefully cleaned of any carbon, which sometimes lodges on the tip of the electrode. The electrode porcelain housing should be examined for cracks. The electrode spark gap must be set at a maximumn of 3/16 inch, which is the distance between the electrode tip and the burner. With these components reinstalled, the LP-gas pressure can now be checked.
A pressure tap can be removed and the line pressure measured with a manometer (U-tube gauge). Those of you who want to perform this test should be thoroughly familiar with LP-gas safety and understand these readings. The input-line pressure for all LP-gas appliances is 11 inches WC (water-column). Your RV-dealership's service center should be equipped to perform this test. However, for the do-it-yourselfer these tools can be ordered from a variety of sources; your RV-parts store can sell you one or order one for you.
Furthermore, a commercial leak-detection solution designed for checking LP-gas connections and fittings should be used. Use the dauber that comes in the bottle to soak down the fittings and look for any bubbles, which indicate a leak is present. Do not get any of this solution on the components of the control system of the refrigerator.
A note about safety should be mentioned here. Do not store any combustible materials or flammable liquids in the refrigerator compartment. Also, when refueling with gasoline, diesel, or LP-gas, make sure the refrigerator is turned off, as well as the furnace and water heater. Since these appliances are externally vented, fuel vapors could be ignited, causing a fire that could result in personal injury or property loss.
During hot weather, units without automatic thermostats must be turned up to MAX in the daytime. Many older models have a high- and low-flame feature on gas mode, while the newer designs feature a thermostat that will turn the flame off when the target temperature is reached. When more cold is called for, it will start a sequence of electronic ignition and cycle back on. If the thermostat is suspect, it can be bypassed by hooking the leads together with electrical tape. If the refrigerator begins operating, replace the thermostat.
The electrical system heating element is what creates the heat source for electric operation. Here, a volt/ohmmeter is required for testing. The correct voltage and wattage rating of the heater is vital to create sufficient heat to circulate the cooling-unit refrigerant. If this is compromised in any manner, the refrigerator performance will be less than ideal or perhaps result in no cooling at all.
Adhere to all safety precautions when working with electrical components. With the electrical power turned off, disconnect the heater leads and measure for proper resistance across the leads. If the resistance is infinite, the unit is defective. To determine the correct ohm-resistance value for your particular refrigerator model, contact the manufacturer or your RV service center.
If these readings are within specifications, reconnect the heater leads. Make sure you observe the correct polarity and that after you turn the electrical power back on, that power is present at the receptacle the refrigerator cord is plugged into.
In newer models with electronic ignition and automatic energy selection, a fair amount of battery power is required for the control to function. The incoming battery voltage can be checked at the terminal block at the rear of the refrigerator; there should be between 10.5 and 13.5 volts DC.
If chronic hot-weather performance problems exist, there is a possibility the ventilation area created behind the refrigerator by the RV manufacturer is not large enough. Ask the refrigerator manufacturer for specifications, measure the ventilation area on your unit, and see if it meets the specifications. In most cases, RV manufacturers adhere to the refrigerator design specifications.
In summary, proper operation can result in better efficiency in hot weather, and there are three major requirements for refrigerator operation. These are: ventilation, a good heat source, and leveling. A few checks of these systems, especially after extended storage periods, will help the refrigerator when it needs the most owner attention.
Absorption-type refrigeration diagram
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