Escapees March/April 2016

Similar to the manual control, the automatic control must perform the safety task of knowing if the LP flame is lit or not. If the controller calls for LP gas to turn on, it sends power to the electric gas valve and the igniter. If the flame does not light, the con- troller senses this situation and turns off the LP gas. This function is easy to test. Turn off your LP gas valve at the bottle and put the refrigerator into LP mode. You can hear an audible click from the gas valve followed by a snap, snap, snap from the igniter arc. After a number of tries to ignite the flame, the refrigerator should shut off the gas valve and alert the operator that there is a problem. (Reference “LP Gas Op- eration” in the November/December 2015 issue.) In addition, the main controller has a sensing mechanism that deter- mines if there is shore power available or not. When the control is in the automatic sensing mode, the logic of the controller is set to check for shore power first. If shore power is avail- able, the refrigerator will turn on the electric heaters to power the cooling unit. If there is no shore power, the refrigerator will attempt to turn on the LP gas if cooling is needed. This automatic energy selector (AES) can usually be overridden by a switch set- ting on the refrigerator control panel that allows you to force the system into the LP gas mode. You can also simply unplug the refrigerator from shore power (at the receptacle in the cooling unit compartment) so that the AES cannot run the refrigerator from shore power. Error Codes Some refrigerator controllers can detect if there is a problem such as the cabinet temperature sensor is not working. The result is to store an error code that can be read out for diag- nostic purposes. See your operator manual to determine if your refriger- ator has error code capability or not. One classic error code is the NO CO error, which is fondly referred to as

Reader comments We have had excellent comments regarding our RV fridge article se- ries; we are glad we have stimulated thought. The initial installment of the series discussed the absorption refrigeration process. I did over-simplify the process and want to respond to some feedback. Two Other Ingredients: Reader: “ It should be noted that, in addition to ammonia and distilled water in the refrigerator tubes, there are two other ingredients. One is a powder that coats the inside of the tubes to reduce corrosion .” The “powder” is called sodium chromate, which is a corrosion inhibitor. So- dium chromate is highly soluble so it dissolves into the distilled water. If the sodium chromate is destroyed, the fridge will fail due to internal corrosion. Boiling the water in the cooling unit concentrates the sodium chromate, and, in turn, the sodium chromate becomes ineffective to prevent corro- sion. The good news, the ARP control keeps the sodium chromate from being destroyed in this manner by preventing the water in the cooling unit from boiling. Simple solutions are the best. Plugged Tubes: Reader: “ This powder can flake off and block up the small orifice at the top of the refrigerator and cause refrigerator failure.” I often hear that absorption refrigerators have a “small orifice.” In fact, there is not an orifice in the RV-type absorption refrigerator. The absorp- tion-type refrigerator does have two tubes that can be plugged by the failure of the sodium chromate or the resulting rust that “flakes off” in the cooling unit. One is the pump tube in the boiler and the other is the weak-solution tube. As mentioned above, as long as the water is prevented from boiling in the refrigerator, these tubes will not plug. Hydrogen Gas: Reader: “ The final ingredient in the refrigerator tubes is flammable hydrogen gas. The evaporated ammonia passes through a small ori- fice at the top of the refrigerator into the hydrogen environment .” All absorption-type refrigerators have what is called an assistant gas to fa- cilitate the evaporation of the refrigerant (ammonia) based on the principle of Dalton’s Law of Partial Pressures. Hydrogen makes the best assistant gas because of its molecular structure. Although hydrogen is flammable, so is ammonia. Dalton would tell you that hydrogen is not the main fire issue because there is not much of it in the system compared to the volume of ammonia. The flammability of ammonia is evidenced by fertilizer plant fires, so ammonia is flammable and is more of a fire problem than the hydrogen. Over the years, helium has been used as an assistant gas, but these refriger- ators have the same issues with destruction of the sodium chromate while still containing flammable ammonia. Absorption refrigerators have been used safely for 150 years. It is the control of the boiler process that is central to keeping the system reliable and safe.

66 . ESCAPEES | March/April 2016 | www.escapees.com