Hi everybody...
I don't know why they don't just go back to using NH3 ammonia gas as a refrigerant. If memory serves me correct, ammonia is one of the best refrigerants known because of it's high heat absorbsion ability. Yes, I know it's poisonous, but there are ways to work around that.
I still think that the expiration of Dupont's patents on the old Freon played a factor in it being banned.
Daniel
If you've ever messed with anhydrous ammonia, you'd understand...
"Poisonous" isn't really the word... the stuff is, being a pressurized liquid, prone to boiling off instantly into clouds of white vapor when the pressure is removed from it, absorbing heat and thus "refrigerating" whatever it touches in the process (which can frostbite you if you're sprayed with the liquid itself, much like propane or butane.) The clouds of gas are noxious, in that if you breathe them in, or the vapors get into your eyes, they are hygroscopic, meaning "water seeking" and thus dissolve instantly in the moisture in your eyes and mucous membranes, like inside your nose, throat, and lungs. This is roughly analgous to inhaling liquid household floor-mopping ammonia (aqueous ammonia). In short, it's like you snorted a bottle of household ammonia and you start drowning in the stuff... no good at all!
My Dad was very nearly gassed by anhydrous ammonia, which is commonly used as an agricultural nitrogen fertilizer, when I was a kid. After that, despite anhydrous being cheaper, he switched to the more expensive but much safer to handle aqueous ammonia, which is ammonia already dissolved in water as a carrier, and thus is not a pressurized liquid that boils in open air, and isn't stored in a pressure tank. Worst that could happen to you with that stuff was getting it in an open cut, where it'd burn like fire, or having it splash you on your skin, tongue, or eyes, where it behaved similar to household cleaning ammonia-- IOW a strong detergent, tasted terrible, and burned in the eyes until it was washed away by eye flushing, and might dry your skin out.
While folks have used propane or butane to as a cheap replacement for R-12, it's certainly NOT a recommended practice... (though an often necessary one, since R-12 substitutes were non-existant or heavily regulated as well). Refrigerants are supposed to be formulated to be non-toxic (at least at the "normal" levels one would expect if an accident punctured the coils and caused an "instantaneous" release of all the refrigerant in the particular system that was punctured, whether automotive or appliance), and it's supposed to be non-flammable, or not support combustion. Ammonia and propane/butane of course don't meet these requirements (though ammonia is a severe irritant and not massively, instantly "toxic" per-se, though it is in large enough concentrations). Honestly, I'd be less afraid of propane as a refrigerant than ammonia, especially in a vehicle-type system... a couple pounds of propane, even vented suddenly by a punctured coil, would basically have to vent and mix with air directly in the presence of an ignition source to ignite... and if the mixture is off, meaning not enough oxygen, or too diluted by mixing with too much air, the stuff won't ignite at all, and even if it does, it would burn off very quickly. Ammonia, on the other hand, would be an inhalation hazard until the wind finally carried it away. In a stationary air conditioning or refrigeration system, I wouldn't want either one...
I've handled propane and butane, as it used to be a very popular (and cheap) alternative (in the 1950's) to gasoline power in farm tractors, before the 'diesel revolution' in the late 60's took hold and basically ALL farm equipment became diesel powered in the early 70's... We had a propane-powered Golden Jubilee Ford when I was a kid, and a propane powered Farmall M several years ago. One day I was filling it from the bulk propane tank, and when I disconnected the fill valve, the automatic poppet valve on the tractor tank, which is supposed to snap shut when the bulk tank hose fitting is unscrewed, stuck... liquid propane started squirting out, and rapidly boiling off into vapor, and soon the parts were thoroughly frosted over, their latent heat being siphoned off by the boiling propane. I tried screwing the valve back on, but couldn't get it to reseal... soon it was too bitterly cold to work with in bare hands, so I went and got my heavy leather welding gloves and used them, but they would soak up liquid propane which would boil off and soon they were freezing up too... I finally managed to get the fill hose unscrewed, and the poppet valve continued to dribble liquid propane, which boiled off into a cloud of vapors that then drifted across the field from our house toward the highway, some 150 yards away, and I was worrying that someone might toss a lit cigarette out a car window and have a gas explosion that would backdraft along the fumes to the tractor and tank, as the vapor cloud drifted on the breeze across the field. I got a 2x4 board and started smacking the sides of the tank filler fitting (the steel fitting welded to the tank into which the brass poppet filler valve was screwed) and it FINALLY snapped shut and seated, shutting off the flow of liquid propane, and the vapors rapidly dispersed... problem solved. My Dad told me later that yeah, sometimes that happens, and yeah, that's how you fix it...
Later! OL JR