Air-Conditioning System

Air-Conditioning System photos: P 28-P 37

Air-Conditioning systems are no different than any other aspect of home inspections. Due to the rapidly changing technology, you have to keep on top of the updated equipment and techniques that are being used in new construction. Find a knowledgeable contractor in your area and buy him lunch occasionally to learn about any developments in his industry.

I'll try to walk you through the basic concept of how an air-conditioning system works. If it seems too technical, don't worry. You only need to know how to decide if the A/C system is operating properly at the time of the inspection. I'm including the inner workings of an air-conditioning system because I believe it's a great help. By knowing this information, you'll earn the respect of the client and any third parties if they ever ask you how the system operates and cools the air.

  1. The basic components of an air-conditioning system are the compressor, condenser coil, receiver, expansion device and evaporator coil. Some newer units don't have an expansion device.

  2. The evaporator coil s what cools and removes excess moisture from the air. It looks similar to the radiator of a car. This is the part that's located inside the house in what's sometimes called the air handler. The air is cooled by using a "refrigerant" which cycles between the different system components.

  3. Freon 12 and Freon 22 are the refrigerants used in most gas compression refrigeration systems for residential use. Freon 12 has a boiling point of below -20 degrees Fahrenheit at atmospheric pressure. Freon 22 has a boiling point of below -40 degrees Fahrenheit at atmospheric pressure.

  4. The A/C cycle starts with the refrigerant (Freon) contained initially in the receiver. The receiver is usually located in the lower section of the condenser. While inside the condenser, the Freon is cooled by the outside air being blown over the coils. The compressor acts as a pump and forces the Freon under high pressure through the liquid line to the expansion device.

  5. The flow of Freon into the evaporator coil is regulated by the expansion device. As the high-pressure liquid Freon is forced through the expansion device, it expands into a larger volume in the evaporator. As it expands, the pressure and temperature are reduced. Due to the low boiling temperature of Freon, it boils when under this low pressure until it becomes a vapor. During this change of state, the Freon absorbs heat from the warm interior house air which is flowing across the outside of the evaporator.

  6. The Freon vapor is pumped out of the evaporator through the suction line to the compressor after it has absorbed the heat from the interior house air. The compressor then compresses the Freon vapor, increasing its temperature and pressure and forces it along to the condenser.

  7. The hot Freon vapor is cooled at the condenser unit by lower temperature air being blown over the condenser coils. This absorbs some of the heat in the Freon. As a result, the Freon temperature decreases until the Freon is cooled to its saturation condition. When the Freon reaches its saturation condition, it will cause the vapor to condense into a liquid. The liquid, still under high pressure, flows to the expansion device and completes the air-conditioning cycle.

  8. Cold is never created during the air-conditioning cycle. Instead, heat is merely transferred from one place to another. When the Freon passes through the evaporator, it absorbs heat from the room air which cools it. When the higher temperature Freon passes through the condenser, it gives up its heat to the air being blown over it.

An air-conditioning system is a closed system, and theoretically, there should never be a need for additional Freon. However, the various fittings on the connecting pipes can loosen or develop small cracks. Any loose connections or cracks can allow some Freon gas to escape. If the air-conditioning system cannot hold a Freon charge for at least one season, then the leaks in the pipes or fittings should be located and corrected.

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