Ammonia on its own is an excellent refrigerant and was used for many years in compressor type refrigeration. It was replaced by the newer cloroflouro hydrocarbons because of the danger when leaks occurred in large refrigeration plants like cool rrooms and meat works.

Absorption fridges work on an entirely different principle and can use a mixture of water and ammonia as the refrigerant, however internal rusting is not a problem as there is no oxygen present in the mixture. Iron needs both oxygen and water to rust and will not rust in the presence of only one. So any breach in the piping of an absorption fridge is either a crack from stress or external rusting.

Alan

Graeme the water doesn't evaporate the ammonia does. The heating element drives the ammonia out of solution in the water and it is the ammonia that goes through the refrigeration cycle and is then reabsorbed into the water away from the heat source. convection then carries the ammonia rich solution to the heat source and the cycle is continuous. All early domestic fridges used this system aka kerosene fridges.

Alan

Dickodownunder wrote:

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Thank you for the warning and the description Grubbygypsy.

Do you know how old your fridge is?

Reason I ask is that I am wondering if new 3 way fridges still use ammonia?

Maybe someone will know.

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 Sorry for my delay.....I've just had the fortnight from hell....including the death of a granddog that I got the blame for......

The fridge was as old as the van - 5.5 years. It was the AES Dometic. I called Dometic over the safety of the rest of the food ie does the ammonia have a residual, and he sounded genuinely surprised that the fridge had blown up to be honest. 

Its now finally replaced and I'm just restocking to hit the road again. I'm unsure if they still have this....I'm assuming yes, as it's how they work...ie 'gas conversion'.

I was also robbed in this period.....so I'll take all the prayers I can get, that when I hit the road tomorrow, I don't get T boned by a roadtrain....

NeilandRaine wrote:

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Just an aside, 3 way fridges only freeze to minus 12,

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Sorry but this story is just so much "old wife's tale". (read that as bullsh!t).

The quantity of ammonia in an absorption (3way) fridge is so very small.
The human nose can detect the smell of ammonia as small as a 5 parts per million. To us humans it has a VERY strong smell. Strong ammonia smells are used to wake faint victims.
If your fridge is leaking slowly the smell seems to linger for a long period. Even in instances where the leak is large and the escape is very quick, in no way would it pose a threat to your health unless you stuck your nostrils right up to a hole in the pipework and at the exact moment you pierced the pipe you inhaled all the expelled gases or stuck your eye in front of the expelling gases.

Liquid ammonia expands to 850 times it volume under 1 atmosphere pressure.
The amount of pure liquefied ammonia in a 90 litre 3way fridge is approx. quarter of a litre (250ml). On release this expands to 213 litres. An amount of gas equal to only approx. 2.5 times the interior size of your fridge.
Anhydrous (no water) Ammonia gas has a tremendous affinity for water and reacts immediately with humidity in the air and becomes hydrous ammonia which is heavier than air and will remain close to the ground. The Ammonia in your fridge is already hydrous. Ammonia leaking from your fridge will remain mostly at floor level and disperse out your van door safety vents.
If released all at once in a 16 foot van it would result in approx. 1 inches (25mm) of hydrous ammonia gas on the floor of your van and yes it will have you coughing and spluttering but within a few minutes would have poured out the safety vents in the van door.
A slow leak in your fridge over a few hours may result in an extended strong smell of ammonia but the concentrations are tiny and within a couple of hours your fridge's pressurised system would have equalised and no longer be leaking.

Your first pee in the morning smells strong because of ammonia. On a cold morning a standing man will inhale more ammonia from his pee than you would get from your average slow leaking fridge. Ammonia based fertiliser known as Urea, gets its name from Urine.
In US conducted safety tests, some individuals exposed to 50 parts per million (ppm) over 10 minutes have experienced mild respiratory irritation, but it takes 500 ppm over 30 minutes to alter your respiratory rate, 1700ppm to induce coughing, and 6000ppm over 2 hours can produce burning in the eyes, nose and mouth and produce progressive cyanosis (lack of oxygenated blood) and eventually death.
The maximum recommended safe exposure is 50ppm over an 8 hour period.

Ammonia is used in a myriad of household products that we use every day with no detrimental effects (unless you misuse the product such as prolonged sniffing of detergents such as Domestos or Handy-Andy).

For those that have ever wondered how an absorption fridge works I'll try and explain their operation in layman's terms. Purists please excuse my over-simplification.

During manufacture the system is first reduced to an almost complete vacuum and then the system is filled with mostly pressurised hydrogen and water and a quite small amount of pure liquid ammonia.
The hydrogen pressure is set to the point where ammonia boils, based on the maximum ambient temperature the fridge must operate in. Ammonia normally boils from liquid to a gas at minus 33 degrees Celsius.
For a 'tropical' rated fridge, at plus 35 degrees Celsius (maximum ambient temp), the dew point of ammonia (the point where it changes form from a liquid to a gas or back to a liquid) is at a pressure of approx. 200psi or around 14 atmospheres of pressure.
The electric heating element (12V or 230V) or the gas pilot flame, is located at the bottom of the pipework and heats the 3 ingredients to a temperature greater than the 35 Celsius ambient (the dew point of the ammonia) and it changes to a gas, bubbles out of the water, up the pipe work and increases the system pressure.
As the hot gas passes over the pipework at the top that looks like a radiator (condenser) it cools (condenses) back to a liquid and the pressure drops.
Just like you have experienced on the outside of your gas bottles when they run low, when the pressure drops it gets cold.
The colder liquid ammonia flows downward it passes through pipework inside the fridge and absorbs heat from inside the fridge as it goes (this is why it is called an absorption fridge).
Cold doesn't radiate coldness, heat radiates heat, cold absorbs heat.
It then re-mixes further down the pipework with the water and flows back to the heating area and the cycle repeats.