I have spent the last couple of weeks exploring and adjusting my fridge
, and I have learned a lot, so I thought I would summarize it in case others find it useful. I have an Escort Mini-15, a 3-way tiny fridge
with no freezer compartment, which was the original fridge
in our 74 Winnipeg Neonex Boler
. I got a lot of information from the internet.
There are 2 kinds of RV fridges, compressor and absorption. A compressor fridge is like the one at home, and is much more efficient on electricity. However, it cannot run on propane
gas, and so absorption fridges remain popular for trailers.
An absorption fridge works on heat. There is a great website for information at RV Mobile http://www.rvmobile.com/tech/Trouble/Index.htm
. Basically, a heater heats up the cooling tubes filled with an ammonia mixture (the cooling unit). When hot enough, the mixture boils and separates into its parts and evaporation runs around the tube, cooling eventually and returning to its original state. Part of the tubes are in the fridge compartment, which then gets cold, which cools the food. Not technically accurate, but close enough.
The thing to know is that the heat has to be just right. Not enough and the mixture doesn't boil, so no cooling in the fridge. Way too much and the fridge can eventually burn out. Also, if the trailer is not moving, the fridge must be reasonably level so that the mixture can circulate, otherwise it can burn out somehow (I don't understand that part). If the trailer is moving, level is not such an issue because the mixture is in motion as well.
The heat can be supplied by any source, and the cooling unit is the same one no matter which source heats it up. In my 3-way fridge, I have a 110V heater element, a 12V heater element (these two are built into one physical structure), and a gas burner, all of which heat the same cooling unit.
The two possible areas of problems are the cooling unit or the controls. Since the cooling unit is heated by any of the heat sources, therefore, if the cooling unit works well on any of the sources, it is OK. If you smell ammonia and have not cleaned the trailer recently, probably the cooling unit is leaking, which calls for a professional repair.
Last year my fridge worked well on 110V and gas, but not at all on 12V. With many responses to my thread on this forum, I eventually figured out that the connections were dirty, cleaned them, and it has since worked well on 12V. Too well in fact.
This year when we went out on our first trip, I discovered that the fridge would freeze water on electricity in a few hours even though we have no freezer compartment. This was on 110V. I only had the 12V on for a couple of hours, but it got really cold too. Conversely, the gas would only cool the fridge down to 46 degrees F. I put a thermometer in the fridge to find out what the temperature was.
A fridge should be around 36 - 38 degrees F to keep food from spoiling. The good news was that I was sure the cooling unit worked, so this left the controls as the problem. I was able to remove the control panel from our fridge in the back from the outside of the trailer without having to remove the fridge.
: Disconnect the 110V and 12V voltages first. My fridge is wired this way: the hot wire from each of the 2 voltages (110V and 12V) comes to a DPDT center off switch. When switched to either selection, the selected voltage is sent to a simple on-off thermostat. The output of the thermostat goes back to the DPDT switch which then sends the voltage to the 110V or 12V heater element, whichever is selected. The ground or neutral side of the voltage is connected directly to the heater element. This means that the switch and the thermostat only interrupt the hot side of the circuit. The center off position is used when running on gas.
The original electrical
thermostat was a Teddington Type KCA. Teddington is still in business, but they don't make these things any more. The thermostat only has two connections and a tiny capillary tube that senses cold and runs into the fridge itself. It looks like a wire. If the capillary tube gets squished or kinked, then the thermostat won't work, but this can often be fixed by straightening it out. My thermostat gave audible clicks when going through the temperature range, but did not shut the current off at all.
By the way, the fridge has to be cold to test either the gas or electric thermostats, since they only operate in cold temperature ranges.
Anyway, when I removed the thermostat from the circuit, the electrical
terminals were badly charred, falling apart. This explained why the thermostat would audibly click on and off in a reasonable range for the temperature, but the thermostat would not actually shut off the current to the heater. Knowing that I could never get an exact replacement, I was contemplating rebuilding it from scratch, a daunting prospect. However, it turned out to be easier.
The job the thermostat does is simple: it turns the current on or off when the temperature in the fridge rises or falls. Knowing that there were many fridges then and now that work the same way, I called the local RV fridge specialty shop (Cool It RV) and took my thermostat in to them. The old guy there had actually seen my brand before, and got me an old-stock similar sized replacement. The new thermostat is a Ranco model K50, which is still made today. It was small enough to fit into the same space behind the old control panel, but used a different size knob (which I can easily live with). It required no modifications to mount on my original panel. After a couple of days of testing, I found the right temperature range and marked it with a felt pen. Works great.
Gas: My gas system has the gas from the main tank regulator going to a shutoff valve at the fridge control panel. This then goes to the pilot light
switch and thermocouple, then the thermostat, then out through the gas orifice to the burner. My gas, once lit, stayed lit, so I knew that the pilot switch, thermocouple and gas lines worked OK. My problem was not enough heat, although I knew it was close because the fridge would cool to 46 degrees F. That was good, just not good enough. If the heat was much too low, the ammonia would not boil at all and there would be no cooling at all.
I found out that the gas thermostat was working by first cooling the fridge on electricity, then lighting
the gas. When I adjusted the thermostat knob, I could see the flame change from higher to lower intensity. A gas thermostat on these old fridges does not actually shut the flame off, because then you would have to relight it. Instead it switches from full blast to pilot light
, then back again when needed. On my fridge, the thermostat would change in the correct range when the fridge was cold, so I knew it was OK.
This leaves gas pressure and the orifice as the possible culprits. I decided to check both. The orifice was cleaned according to internet instructions in alcohol, then blown out with compressed air from my portable air compressor used for blowing up tires
, then cleaned in alcohol again. After this, I could see two tiny holes in the end of the orifice, where I was expecting one. The guy from Cool It Rv told me that this was not unusual, some orifices do have two holes. Besides, since my problem was not enough heat I figured it would not hurt to have two holes there anyway. The internet says that you should clean the orifice every year or so. I doubt it had ever been done before on mine. Next came gas pressure.
The internet says that absorption fridges are more demanding of correct gas pressure than any other appliance in the trailer. Obviously, the more gas pressure getting to the gas orifice, the more heat. To measure the correct pressure, you must have a manometer. I built a cheap, easy and accurate manometer with instructions from the internet here: http://www.rverscorner.com/manometer.html
I disconnected the gas tube to the orifice (gas off, of course) and attached the manometer to the gas where it outletted from the control device. I used common electrical tape to temporarily seal the plastic tube to the gas line. This is the gas pressure that actually goes to the orifice, after all the controls have had their say. By the way, this gas pressure is extremely low. 11 water column (WC) inches is something like 0.5 psi.
So, turning on the gas, the pressure measured 10.5 WC inches on my scale. Not quite good enough, so I adjusted the main system regulator from the propane
tank so that the pressure was 11 WC inches. Didn't know that many regulators can be adjusted? They can be, but don't do it unless you actually have a measuring tool such as the manometer. It is a precise operation.
After adjusting the pressure (which also increased everything else in the gas system, but the furnace
and stove work fine with the right pressure also) and reinstalling the orifice, and blowing compressed air up the burner chimney in case there were any spider nests blocking the vent, and checking the gas connections with soapy water for leaks
, I started the fridge on gas and cooled it down to operating temperature. I know that electricity is much quicker, but I wanted to see if the gas would do it (which it did). I have often heard that gas is only used for maintaining the temperature once you get there using electricity. I then set the gas thermostat in the right range, and left it for 12 hours. Later, the fridge was still in the 36 - 38 degree F temp range. The next day, it was still in the right range.
Mission accomplished. We can now put food in the fridge and travel with confidence that whichever source of power we use will keep the fridge working and our food will be OK. I know that fridge efficiency depends on the outside weather as well, so we may have to adjust the thermostats in really hot weather, but at least we are in the ball park.