Hi Could some one please explain how these absorption fridges work in relation to the thermistor. Thetford N3185
On 240 v mine draws around 1.4 amps, so rated at 300 w this seems ok but it never seems to change or cut out. As the thyristor gets cools shouldn't the current decrease in proportion to temp setting and then shut off occasionally when it gets down to temperature ?
Does the thermistor affect the gas setting, ie should the gas shut off when the fridge gets to temperature ?
I assume on 12 v it just stays on all the time to maintain temp.
Regards Ian
-- Edited by Ian G on Wednesday 19th of November 2025 07:38:42 AM
A thre way fridge is the same as kerosene or gas. Uses heat to gasify the ammonia which then returns to liquid by taking heat from fridge. The 240v is using an element to provide the heat, but not very efficiently. I am surprised it is only drawing 1.4 amps.
I grew up with kero fridge and I refuse to go back to that old technology in my motor home. Risk of fire and lack of efficiency is my concerns.
1.4 amps at 240 volts is 336 watts ... varies a bit with actual voltage. On my Dometic RM4601 the specs show the element as 325 watts.
When running on 12 volts they usually use a different element, probably a bit smaller wattage than the 240 volt one.
I don't know about your fridge but this is the way the thermostat works on mine:
12 volts - ignored. Fridge runs constantly.
240 volts - cycles on and off. Full cooling then totally off.
LPG - adjusts flame as target temperature set on the dial becomes closer. Never turns off fully. When days are hot and nights are cold it tends to overshoot the cooling at night, so I adjust it a little.
LPG will usually be the most effective.
-- Edited by Are We Lost on Wednesday 19th of November 2025 03:08:19 PM
Just returned from a short trip to southern NSW, was quite warm around 30 every day. Fridge would get to -12 deg in freezer and 2 deg in fridge at night but during the afternoon freezer would come down to -2 and fridge 15 deg. Running on gas only
I moved the thermistor up but that didn't make any difference. I noticed the relay click a few times so I assume the gas was cutting in and out and giving the high temp I would have thought it would be on all the time.
I think I will change the thermistor
Ian, before you replace it, try moving the thermistor probe away from the evaporator to a warmer area so the fridge will run longer before it senses the temp to shut off .
On my fridge I pulled if off the evaporator and just let it hang down from the evaporator . works much better there.
One trick that worked with kero fridge is if not cold then turn slightly warmer. NOT colder.
When the temperature drop is too great for the setting and outside temperature they tend to spit the dummy. You might be able to maintain 8 degrees instead of the 15.
The reason as I understand is ammonia will only drop temp by a certain number of degrees. If the setting is lower than that it just quits or almost quits.
Some chemistry expert can probably explain that better than me, I just know it worked for us before we had power.
Thanks, I checked the thermistor, it sits on around 10k ohms at room temp and increases significantly when you put it in a glass of cold water, so that seem ok. I will try it with the thermistor off the evaporator. May even change the gas regulator.
