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The mysteries of the gas fridge (3 way fridge)
Following on from the technical evening at the 2016 AGM where there were several questions and comments regarding the workings of the gas side of the fridge, so I thought the following may be of use to some members. This article is, to the best of my knowledge, correct and is intended for information purposes only, as you are probably aware only Gas Safe engineers trained in LPG should undertake this type of work. (C.O.R.G.I. is no longer the governing body for gas installers).
This information is based on an Electrolux RM4213 (which we have in our Murvi)
When switching on the orange illuminated switch, which then starts to flash and make a ticking sound you have powered the spark generator, this causes the electrode above where the flame will be, to produce a series of sparks from the end of the electrode to the metal frame (earth) this will continue until a flame is established which will conduct the electrical current through the flame (combustion, “burning gas” is a chemical reaction which produces electrically charged particles which will allow an electric current to flow through a flame) making a circuit and stopping the spark generator from sparking, if the flame goes out for any reason the circuit will be broken and the generator should start sparking again.
When holding in the gas fridge control knob you are manually holding open a gas valve (thermo-
electric valve) to enable gas to flow to the burner, when the flame is lit via the spark generator the flame heats the end of a thermocouple, this produces a low voltage current (millivolts) which creates a electrical curcuit up to the valve you are holding open which acts like a solenoid (electric tap) which holds the valve open for you enabling you to let go of the gas tap, if the flame goes out, the tip of the thermocouple will cool, no longer producing an electric current and the gas tap (fridge on-off control) will close shutting off the gas supply to the fridge.
The thermo-electric, thermocouple arrangement is also used on the gas hob, if the end of the thermocouple is corroded or damaged then it will not work ie produce any current when heated.
Things to bear in mind
As well as the vents in the door with the removable panels for warm weather, at the bottom of the fridge in the floor of the van there are vents. These are important as LPG is heavier than air, in the event of a gas leak these will allow the gas to drop out and not build up, an air supply is also important for gas to burn safely. If you own a Murvi with gas bottles installed inside the van and connected with hoses, these hoses should be date stamped and it is recommended that they are changed every five years. Washing up liquid should not be used to check for gas leaks as it can be corrosive if not washed off, cans of leak detecting spray are available at plumber’s merchants as are small cans of compressed air which can be useful to blow in around the burner to dislodge any unwanted deposits. Flames should be steady and blue, if there is yellow in the flame and or it is unsteady the appliance should not be used until this is rectified. No doubt you will all hopefully have a working carbon monoxide detector in your van!
I have included a picture of the fridge burner for information purposes, showing the components and a nice blue flame.
Regarding the 12/230v operation of the fridge both of these have an element fitted next to the heat exchanger to provide the heat.
If you wish to know how heat makes the fridge cold please click on or copy and paste the link below.
http://www.campertrailers.org/3-way_fridge.htm
not sure about this one but it might be of interest.
http://caravanchannel.proboards.com/thread/4306/fridge-working-turn-upside
Stay safe!