Whether the unit in question is a home furnace or an oven, gas-powered appliances generally feature pilot light assemblies as a core operating component. These are connected to a gas supply line monitored by a thermocouple. These heat sensors are connected to both the pilot light and the incoming gas supply line and shut off the gas flow when the presence of heat is no longer detected to prevent leaks or hazardous buildup. Particularly when the unit is inside of an RV, thermocouple failure in a gas refrigerator can lead to a minor panic, especially if you're on a road trip when the fridge stops working. Thankfully, testing and replacing a refrigerator's thermocouple is a fairly easy task with basic screwdrivers, a multimeter and the right safety precautions.
Thermocouple in the Refrigerator
While the presence of a thermocouple in a refrigerator may seem odd, especially to those renting RVs for the first time, gas-powered fridges are not uncommon in RVs as well as in normal homes. The only real difference between a gas-powered fridge and an electric fridge is the component used to move refrigerant around the cooling system and the refrigerant used within that system. In the case of gas-powered fridges, a boiler is used in conjunction with a combination of liquid ammonia, water and hydrogen rather than the compressor and HFC or Freon used in electric refrigerators. With those exceptions, a gas-powered fridge works off of the same principles as an electric one.
Safety and First Testing
Before attempting to test and potentially replace your refrigerator's thermocouple, check the owner's manual that came with the unit or look online for your model's manual if you don't have it on hand. It will list the exact model of your fridge and will hopefully contain a list of compatible replacement parts along with information on the unit's warranty.
While replacement of a thermocouple is simple, DIY work with gas systems can be dangerous. If you're uncertain how to proceed, especially if your unit is still under warranty, it may be a better idea to call a service technician to test the thermocouple and replace it if faulty than to attempt this work yourself. If you choose to proceed, take note of the model and the listed replacement parts, and then trace the gas line from your fridge until you find the gas shut-off valve. Turn this handle or knob as far clockwise as possible to turn off the gas, and if your fridge runs on electricity as well, unplug it or turn it off via the breaker box, if necessary.
Give the fridge an hour or longer before proceeding. Even if your thermocouple is failing, it may still be dangerously hot when you turn off the gas and/or electricity. Locate your refrigerator's thermocouple by removing its service panel, which is generally located either behind the front grate, within a panel at the back of the fridge or accessible through an exterior service panel on an RV. Examine the area for rust, dirt, soot or similar materials and if present around the thermocouple, clean them away. Occasionally, these things can prompt a thermocouple to give off the wrong readings. If the area was particularly dirty before cleaning, you can restore power and gas to the fridge and see if the pilot light stays on.
Further Testing and Thermocouple Replacement
If cleaning the area doesn't solve the issue, turn everything off again, allow the thermocouple to cool once more and then disconnect the thermocouple's wire or wires from the terminal block/switch. These can either be slid off or unscrewed. Confirm that your multimeter has continuity by setting it to read ohms and touching the leads together. The meter should read 0 or very close to it. Switch the settings to read millivolts, and then connect your meter's test leads to the wires of the thermocouple. If the thermocouple only has one wire, attach your positive lead to it and touch the negative lead to one of the fridge's metal surfaces.
With your meter ready, restore the flow of gas and turn it to the "pilot" setting. Then, press the ignition until the pilot light comes on. Hold the ignition to bypass the thermocouple, and then give the heat sensor roughly 30 seconds to heat up. The flame should be steady and mostly blue, and the thermocouple should be about half an inch inside the flame. If it isn't, the problem may be that it needs to be recentered, and it should be adjusted after turning everything off and letting the thermocouple cool. If it is, check your multimeter to see if the thermocouple is giving off a signal. You should be reading at least 25 millivolts – any less, and the part should be replaced. Ideally, this can be done by ordering the same part listed in the owner's manual, but if that part is no longer available, a universal part found online should work. Just make sure the unit is compatible. If necessary, be specific in your online searches. As an example, search for a "Dometic 2652 thermocouple" rather than a "Dometic fridge thermocouple."