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March 21, 2012 - Larry DeHays
COOLANT, REFRIGERANT, WATER, FREON, FANS, WHAT KEEPS US COOL? Various terms are bandied about, refering to car air conditioning and car engine cooling, two things that are very different. First some definitions; There is no such thing as cold. There is only heat, and lack of heat. The engine cooling system and the air conditioning system are heat transfer systems, which make something cooler than it was before by making something else hotter than it was before. Internal combustion temperature in the engine reaches over 1,000 deg F, which is enough to melt aluminum parts, so we have to cool the engine down to a temperature that will not cause damage. Coolant, sometimes called anti-freeze, is the chemical that goes in the radiator, mixed 50/50 with water, to keep the car's engine cool. It is mixed with water because we need the properties of both to get the job done. Water is the better conductor of heat, but it has a boiling point (112 deg F) that is too low to be practical, so coolant is used to raise the boiling point, and then the whole system is pressurized to raise the boiling point even more to about 260 deg F. Why pressurize it? Well, if you're old enough to remember pressure cookers, they work on the principle that water under pressure has a higher boiling point, therefore the food can be cooked at a higher temperature, which means less cooking time, and more tender beef, especially with carrots and potatoes. But I digress, and I'm getting hungry. Other advantages of coolant are that it has a lower freezing point, which is why it is called anti-freeze, which concerns our northern friends more than it does us, and it has a lubricant and rust inhibitors which are lacking in water. Once the heat from the engine has been absorbed into the coolant mixture, it has to be dissipated into the air by running it through a radiator with a water pump, and driving air through the fins of the radiator with a fan. If this seems complicated, it is. Everything involved has to be in good working order to take temperature from over 1000 Deg F. to around 200 deg F. Most modern cars have thermostats set around 190 Deg F., which sets the lower limit. The upper limit is controlled by the amount of air blown through the radiator, usually holding it under 225 deg F. If the fans don't blow hard enough, it will overheat. If the water pump is weak, or the radiator is restricted for water flow or air flow, it will overheat. If the coolant level is low, it will overheat. If the pressure is lowered, or the coolant mix is diluted, the boiling point is lowered. If it overheats to the boiling point, the coolant will boil out, and with no coolant in the engine, the aluminum parts and other things will begin to melt or crack. Bye bye engine.
News flash. None of the above concerns the air conditioning system. It is also a heat removal system, taking heat from the passenger compartment, which can be 130 degrees F, and dissipating it into the air outside. Is it any wonder that the air outside is getting hotter? The chemical used to transfer this heat is called a refrigerant, sometimes called freon, (which it is not). Heat is absorbed from the interior by blowing air through an evaporator under the dash which contains refrigerant, which takes the heat out, pumped by a compressor through the condenser, which is like a radiator, and another fan blows air through the condenser to push the heat out into the atmosphere. If either of these fans quits, it won't cool. If the compressor doesn't pump, it won't cool. If it gets low on refrigerant, it won't cool, if it's internal filters plug up, well you know the drill by now. Lots of things have to work together to keep us cool. Now where's that beef?
By the way, you know the adage "You are what you eat"? Well cows are vegetarians, so they are vegetables, so it's ok to eat them.
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