The substance used in refrigeration to remove heat from an area and carry it away. It generally boils in atmosphere at a much lower temperature then water and has certain properties.

• Non-toxic
• Not explosive
• Picks up heat easily
• Volatile at working temperature

Different refrigerants are used depending on the application. Freezers generally use R22 whilst ordinary refrigerator cabinets use 134A, R12 or one of its replacements.

Historical refrigerants include ammonia and sulpher dioxide and R12. Ammonia was dropped due to its anti-social effect (it stinks) and explosive properties. R12 was used up until recently and still exists in older refrigeration systems. It use was stopped due its ozone depletion potential, in fact it's the benchmark against which all other substances are compared. Other substances that have been used as refrigerants include diluted anti-freeze, brine, some acids and carbon dioxide.

R12 and its colleague R22 where developed in the USA prior to World War II but did not reach the likes of the UK until after the war. R22 is still used today but R12 has been replaced by a slew of substance with similar properties which are still ozone depleters although to a lesser degree than R12.

Matter exists in three states: solid, liquid, gas.

When a solid melts into a liquid or a liquid evaporates into a gas, it is able to absorb huge quantities of heat. Put a pot of water on a burner. Its temperature gradually climbs to 212°F (or, more eloquently, 100°C) and it starts to boil. Out of the dancing bubbles comees vapor: evaporated water. Hold your hand over the pot. You'll be wrapping it in ice if you hold it too close. The vapor carries tremendous heat into the air above the pot. So much so that the temperature of the boiling water will not climb above 212°. Such is the potential for heat absorption in changed states of matter.

Every liquid has a boiling point. As you know, water starts to bubble up at 212°F. Nitrogen's boiling point is much lower. Remember it in Terminator 2.

Yes, I know this is about refrigerant. Actually it's about the refrigerant coursing through the air conditioning system of your car.

I know. Hold on.

Under pressure, boiling points rise. Our air is packed into our atmosphere densely enough to result in a pressure of some 14 pounds per square inch. We have ways to manipulate pressure — compressors, our own cheeks when we drink out of straws. Empty an aerosol can in one prolonged spray and feel the chill on the can afterwards, like ice: this is the relationship between pressure, temperature, and the absorption of warmth by changes of matter.

Cars are beautiful.

I'm not talking about the outside of a car. I see a '67 Mustang, I see a car with a shapely body, but no beauty. I don't start drooling until you pop the hood.

A car's air conditioning system works by the manipulation and circulation of refrigerant. Heat gets into the cab from several different places — the sun outside, the engine, heat captured by the earth radiating up.

Historically, most automobiles have used refrigerants R10 and R134a. R10 is a hydrofluorocarbon, so we don't use it anymore. All cars manufactured since 1992 use R134a.

A series of (un)unfortunate events

Air conditioning systems are equipped with compressors. Again, boiling points rise under pressure. In the case of a refrigerant in an automobile, it's compressed so that its boiling point rises from about -11°F¹ to 50° or 60°. Because compression also increases the temperature of the substance itself, the refrigerant is a very hot gas when it leaves the compressor.

From the compressor it moves to the condenser, a series of tubes and fins with enough surface area to absorb the heat. Warmth is rapidly transferred to the outside air while the refrigerant is able to condense to a liquid, thanks to the higher boiling point created by the pressure of the compressor.

Next the refrigerant builds up behind an expansion valve; as it passes through, its pressure drops significantly, bringing its boiling point down. As it enters the evaporator, it is just about to start boiling.

In the evaporator, heat is transferred from the passenger cab to the refrigerant. The higher temperatures cause the refrigerant to evaporate, absorbing huge quantities of heat. Warmth is drawn out from the inside of the car and the refrigerant, now a liquid at fairly low temperature, returns to the compressor.

¹With a boiling point at atmospheric pressure of -11°F, you could boil refrigerant in a household freezer.

Schwaller, Anthony E. "Total Automotive Technology, Fourth Edition." Thomson/Delmar, Clifton Park.

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Re*frig"er*ant (r?*fr?j"?r-ant), a. [L. refrigerans, p. pr. of refrigerare: cf. F. r'efrig'erant. See Refrigerate.]

Cooling; allaying heat or fever.

Bacon.

© Webster 1913.

Re*frig"er*ant, n.

That which makes to be cool or cold; specifically, a medicine or an application for allaying fever, or the symptoms of fever; -- used also figuratively.

Blair.

© Webster 1913.