Diamond DaveSee other Advice articles filed in ‘Running a motorhome’ written by Diamond Dave
The fridge is a wonderful invention, isn’t it? Without any effort from us it can keep our food and drink cold and fresh for days on end. However, while this may be true for domestic fridges at home, it isn’t always the case with those fitted in motorhomes.
The most popular units are powered by three different types of energy: 230V when on sites with electric hook-up facilities, 12V while driving, and gas when on sites without hook-up facilities. These units are very similar to our domestic fridges in terms of servicing requirements where the electric side of things is concerned, but they do need regular maintenance to the gas part. Here, I am taking a look at how they work and the care they require.
Three-way fridges (as those that operate via a trio of supplies are called) work via a different system to our fridges at home. Domestic units use a compressor to pressurise a gas that is then forced through small orifices; when it is allowed to expand it absorbs heat from its surroundings. This heat is then carried to the outer section of the cooling circuit, where the heat is dissipated. That, in very simple terms, is how a compressor fridge operates.
Three-way fridges, on the other hand, use heat to create a ‘thermo syphon’ motion in the cooling circuit: as the heat is absorbed into that circuit, the gas inside rises and creates the flow through it. The heat that is required to provide the energy can be created from a variety of power sources: 12V DC when the engine is running, 230V AC when on electric hook-up, and gas when not on hook-up or when the engine is off.
Keep an eye out for blockages
The downside of a three-way – or an absorption fridge, to give it its proper name – is that it’s not the most efficient system. This means that it takes longer to cool down initially, and will require more energy to keep the temperature down (although this can be offset to some extent with better insulation). Compressor fridges, on the other hand, are more energy efficient and cool faster; however, they can only be powered by an electrical source – either 12V DC or 230V AC – rather than additionally by a gas alternative.
There is a problem with running a fridge on gas, and it stems from the fact that only a small flame is required (most three-way fridges require somewhere between 100 and 150 watts of energy to operate). Because of this, the metering jet is a very tiny aperture and as such it can easily become blocked.
In contrast, the air holes are quite large – and small spiders are rather fond of making their nests in the base of the burner assembly! Consequently, this restricts air flow and causes a fuel-rich mixture to appear at the burner. This in turn creates a dirty flame that generates a lot of soot, and carbon monoxide – which, of course, is deadly.
Service your fridge and stay safe
Fortunately, the solution is quite simple: the fridge needs its gas burner and metering jet cleaned routinely, along with any sooty deposits that might have started to build up around the flue. An annual service is advised by both Dometic and Thetford for a fridge that gets average use on gas; more frequent servicing is necessary if it is extensively used on gas.
Many owners mistakenly believe that the fridge will be serviced during a habitation check or caravan service, but this is rarely the case. In my workshop I service the gas side of fridges if possible without removing the unit, but most workshops don’t do this as a standard part of an inspection or service. As the customer, you need to ask whether it will be done; if not, ask for it. There will obviously be an additional charge – but it might just save your life.