To the uninitiated it may not make sense that in a gas fridge you use heat to cool the contents. I will try and make sense of this for you. The correct term is an Absorption Fridge. It is a self contained sealed system and there are no moving parts.

The cooling system consists of five main parts - the boiler (where you see the flame burning from the gas supply), the separator, the condenser, the evaporator, and the absorber. It is a sealed system comprising ammonia, water, hydrogen and an anti corrosive agent.

In very simple terms the cooling takes place in the evaporator (which is inside the freezer compartment) where it uses hydrogen and heat to turn the liquid ammonia into a gas. The heat that this process requires is extracted from the food storage space therefore making this space cold.

The rest of the cycle ensures the ammonia and hydrogen recirculate in the correct state (liquid or gas) to return to the evaporator to cool again. The ammonia and hydrogen gas leave the evaporator and pass down to the absorber via gravity where the ammonia mixes with water, and the hydrogen is free to rise to the evaporator and be used for mixing with the ammonia and cooling again. The ammonia and water mixture return from the absorber to the boiler via gravity, where it is heated to boiling point releasing ammonia bubbles. The separator separates these bubbles from the water – the water returning to the boiler system for reuse. The bubbles (or ammonia vapour) rise with heat to the condenser at the top of the unit where air passing over the fins removes heat from the vapour and turns it into a liquid. This liquid falls with gravity to the evaporator for the cycle (cooling) to commence again.

The fridge does need to be level for all this to happen. The heat source raises the solution to the top then gravity takes over and the solutions fall to the bottom again. There is only a slight slope in all the tubes so if you are parked on a slope the solution will not fall through the system efficiently. If you do operate the fridge when it is unlevel and the solution is not moving around as efficiently as possible it may overheat and crystallize, causing particles to float around in the system. These particles may cause blockages in the system.

You may have heard of people turning their fridge upside down to make them work better. This action is meant to help dislodge the crystals from where they are stuck. Ultimately though, as it is a closed system, the crystals are still there and they will block up the system again.

Ventilation is also a very important component of the process. If cool air can not get to the condenser fins the heat will not be removed and the ammonia vapour will not be turned into a liquid. The fridge needs to be vented at the bottom allowing cool air to enter and at the top allowing the hot air generated to escape. Having only one vent will not allow the free flow of air across the condenser fins. It is also important not to have a dead space where the hot air can be trapped.

There are many ways to make the fridge work more effectively. These “tricks of the trade” will be discussed in the next edition.

© 2006 Gail Bennett (motorhominglifestyle.com). If you would like to reproduce this article on your website please contact gail@motorhominglifestyle.com