07-04-2012, 05:01 PM
Trailer: former Boler, now 1980 Trillium 4500
By all means get the general old fridge Dometic service manual, available on this website and others on the internet. It will help you learn the theory of the fridge operation, which will help you narrow down the problem and find the solution. Also look at the RM211 manual on this website, as it has a clear picture of the wiring diagram.
The good news is that your cooling unit works. The fridge uses the same cooling unit for all three power sources, only the way it is heated changes. Further good news, you did not apparently blow fuses when trying to run on electricity. The two electrical sources both use the same physical heater section (with two separate heaters built into one unit), and the same physical thermostat. So, if you know a minimum of electricity and have a digital volt/ohm meter (aka a multimeter) you can find the problem, and probably fix it.
I am assuming that your 110V and 12V power are actually getting into the fridge. Check this first.
Start with the basics. Unplug the 110V power and disconnect the 12V battery FIRST!!! The RM211 has a box which contains the wiring, the thermostat and the voltage selector switch. In the picture below, you can see it in the lower left. A wiring diagram for the fridge (the same diagram as is in the manual) is stuck onto the unit above it. There is a fuse in the 12V wiring inside this box, which often blows. There is also a connector panel that connects the wires coming into the fridge to the wires that lead to the heater, through the switch and thermostat. These connections often become loose or disconnected.
You can easily find the wires that run to the heaters and measure the resistance across them to see if the heater is working. The armoured metal wire tube that runs from the box contains 3 wires: 1 for the 110V line, 1 for the 12V line, and a common ground. They connect to the connection panel inside the box on the right hand side. You can simply put your ohm meter across the ground and either terminal to measure the resistance, then see if it is in the right range for the heater. The manual says that both the 12V and 110V heaters are rated at 95 watts. This means that the 110V wiring should show a resistance of about 150 ohms, and the 12 volt wiring should show a resistance of about 1.5 ohms (very small, you will have to make sure you have good connections on the multimeter to measure this). Make sure you have the source selector switch to “Off”, and not on one of the electric power sources so that the heater is isolated from the rest of the circuit.
If you get those measurements, your electric heaters are probably OK.
That means that the power is not reaching the heaters on the 2 electric sources. This could be the connections, the switch, or the thermostat. You can use the ohm meter to measure resistance all the way from the pins of the electric plug to the switch and thermostat to see if they show a connection. The thermostat should be on maximum to make sure that the connection passes through it.
This should allow you to find the problem element. Then you will know whether you can fix it by replacing it or have to have it serviced by a pro.
Good luck, be patient, have fun.
Originally Posted by burney99
I have a 1980 Scamp
with a dometic rm211 fridge in it. The fridge works and gets cold on propane but does not work on 110 or 12volt. Any ideas on how to get it to worl on all 3 or should I just be lucky it works on propane.