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Earth Sense: Useful to know system information to care for AC
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Home air conditioners tend to fail during the hottest time of the year, just when they are needed the most. Repairs are a job for trained technicians because some parts are highly pressurized and others carry high electric currents. But it’s useful to know how the system operates and what some of the language means.

There are two main units: the condenser, found outside the building, and the evaporator, which lives in a closet, basement or attic space.

The whole system is charged with a refrigerant gas called R-22. Its price has gone way up since Freon was discontinued for environmental reasons. Typically, a 5-pound charge installed by service companies will cost between $300 and $500.

We cannot produce “cold” in physics. We can only take heat and transfer it out of the house. To do so, we bring a very cold substance (the R-22) inside, run the room air through it and then put it outside.

This is what the evaporator does. Carrying this room heat outside into the condenser, the R-22 now gets compressed by a pump. This makes it build up even more heat, which is removed by a fan. 

Hold your hand over the top of the condenser to feel hot air blowing out. Traveling back to the evaporator in the house, the R-22 now expands strongly, which makes it very cold. The house fan circulates room air through the cold coils, and then pushes it out the vents.

This is where you feel the refreshing cool breeze. To get the air back into the evaporator for more cooling, an air return draws it in and routes it through a return duct. Larger homes have several returns.

The crucial job for homeowners is to replace the air filter, found in the door of the air return, before it gets clogged with dirt. A stopped-up filter overloads the unit and causes ice to form on the evaporator coils. This, in turn, blocks airflow, and only a trickle of cool air comes out of the vent. In time, expensive parts can get overloaded, overheat and fail.

Another good way of ensuring long system life is to not overwork the unit. A room temperature of 78 degrees is adequate for 90-degree days. Running the air conditioning continuously with a very cold setting can wear it out before its time.

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