The typical, RV absorption refrigerator can truly be an enigma of sorts to most RV owners. It is also a workhorse, often taken for granted. It’s been that way for many years. Silent, void of moving parts and usually quite efficient, the RV refrigerator has seen many advances in technology since its inception. From the early days of manually lit, constant flame units to today’s fully automatic and energy efficient boxes, all RVers have enjoyed the benefits of on-board refrigeration during RVing forays. Execute a quick, rearward glance into history and you will find a heyday in which the manufacture of RV refrigerators was quite prolific with as many as eleven different makers in the field. Today, however, that number is reduced to two major players, Norcold and Dometic, though Atwood is entering the arena with a new type of helium (instead of hydrogen) refrigerator, (check this out). This article is not intended to convey operational differences between these two manufacturers; rather, its purpose is to bring to light their similarities and common issues regarding the very heart of any absorption system, the cooling unit itself.
The cooling unit is a weirdly constructed apparatus of tubes within tubes connecting the four major components. Many seasoned RV technicians already understand this, but cooling unit failure, regardless of cause, always mandates a replacement; not an inexpensive proposition for coach owners. This magnifies the importance of an annual and aggressive preventive maintenance program to ensure optimum performance of the refrigerator.
The contents of the sealed system include water, liquid ammonia (and associated vapors), hydrogen gas and sodium chromate, a rust inhibitor used to line the internal tubing to protect it from the corrosiveness of the ammonia.
Upon leaving the evaporator sections, the weakened ammonia liquid then flows through the absorber coils. Here the hydrogen gas rises back up to the evaporator sections while the liquid ammonia is mixed with water in the absorber coils. This mixture now flows to the absorber vessel and back to the boiler and the next cycle begins.
The percolator tube (blue/yellow tube) will be positioned
Here, the cutaway percolator tube is nestled inside one half of the boiler section. Remember, there are quite a few “tubes within tubes” inside the cooling unit.
Because of excess heat in the boiler section, the rust inhibitor crystallized, solidified and completely blocked the percolator tube.
Though a blocked percolator tube is but one cause of rendering a cooling unit faulty, by far the largest cause of unit failure today is due to leaks in the tubing, especially in those areas imbedded in the polyurethane foam block which surrounds the evaporator sections. It’s been estimated that as many as 85% of cooling unit failures are due to leaks in these areas. Here’s why.
After fully charging the cooling unit, the boiler section is temporarily insulated and a “shop” heating element is installed. Each unit is test run on 120-volt AC electricity to be sure the evaporators ice up, proving a successful recharge.
Next, the cooling unit is fitted with a new foam pack, encompassing the evaporator tube set. The new foam is injected into a specific mold affixed to the unit.
Rebuilt cooling units are tagged and warehoused. They are then boxed and shipped to an RV distributor or directly to the service shop.
Though modern absorption refrigerators are a little more forgiving than older designs, the best thing any RVer can do to protect the refrigerator is to always get it as level as possible when it's in operation with the coach is sitting still, and to annually perform a clean & service procedure. A well-maintained and correctly operated absorption refrigerator can last a very long time. Personally, I have seen RV absorption refrigerators still performing well at 40 years old! And do remember that RVing is more than a hobby, it's a lifestyle!