Practical Caravan



MOST CARAVAN FRIDGES are absorption or three-way models, which use heat to make cold.

Put simply, the heat source – whether that’s a gas flame, a mains-powered heating element or a 12V heating element – boils a liquid in the cooling unit, turning it to vapour.

This flows around the cooling unit, owing to a thermosyph­on action (heat rises, cold falls) and as it moves through the sections, eventually turns back to liquid. The change of state takes energy (in the form of heat) from its surroundin­gs, resulting in cooling.

Caravan fridges are pretty power hungry, requiring up to 150W for a large fridge-freezer.

This means when you’re not using mains power, the only realistic source is gas; running a fridge on 12V would soon kill your batteries.

A second issue is that the gas jet can become blocked, as can the air holes, leading to poor combustion – which is a very bad situation. First, the fridge won’t cool well, because the flame isn’t producing enough heat energy.

Far more importantl­y, it will produce quantities of carbon monoxide, the silent killer.

Another issue is less obvious. The pipework of the cooling unit has a finned aluminium plate attached on the inside rear wall of the fridge. This is a good heat conductor, so helps to transfer energy from inside the fridge to the cooling unit.

Heat transfer

There should be a layer of thermal transfer paste between plate and pipework, which aids heat transfer. Often, the paste is poorly applied, but it also dries out, so a simple measure to improve performanc­e in these fridges is to remove the plate (usually secured with a few screws), clean off the old paste and apply new.

You can buy the paste online; I’d recommend a metal-based paste, as these contain particles of aluminium and silver, both excellent heat conductors.

A thin layer on the surface of the pipes where they contact the plate is all that’s required. Dave Newell

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