Q: I want my old air conditioner to run as efficiently as possible. If my cooling costs are still too high, I may replace it. What can I do to tune it up myself?
A: It is wise to make sure your existing central air conditioner runs as efficiently as possible to reduce your electric bills. Because actual cooling costs depend on weather conditions, they vary significantly, making accurate comparisons difficult.
The easiest way to determine the savings from installing a new air conditioner is to compare the seasonal energy efficiency ratio of your existing model to that of a new model. You can be pretty sure your existing unit is not operating more efficiently than when it was new, so savings will be on the conservative side.
Installing a more efficient model offers additional savings. Electric utilities must provide enough electricity generation capacity to meet peak demand. If peak electricity demand can be decreased by homes running newer, higher-efficiency air conditioners, fewer power plants will have to be built. The enormous cost of building a power plant is a factor in rates.
You can do some things yourself to keep your air conditioner running efficiently. This does not preclude having regular professional service calls. Technicians have special equipment and pressure gauges to check internal components of the system, which is impossible for homeowners to do on their own.
It helps to understand how an air conditioner works. It operates on a delicate balance of air flow rates over the indoor and outdoor coils and proper pressures of the refrigerant. The compressor makes the refrigerant very hot. The hot liquid is hotter than the outdoor air, so it loses heat to the air through the condenser coils.
The cooler refrigerant then goes through an evaporator, which makes it very cold. This is similar to how your skin cools off when perspiration evaporates. The cold refrigerant flows through the indoor coil. The blower moves indoor air over the cold coils, which cools your house air. At the same time, water condenses on the cold coils so the indoor air is both cooled and dehumidified.
Getting adequate air flow through the outdoor condenser coils is important for efficiency so refrigerant will be colder when it gets indoors. Make sure weeds and shrubs do not grow too close to the outdoor unit and impede air flow. Don’t rest rakes or other items against the unit, which also may block air flow.
Switch off the circuit breaker to the unit and remove the outdoor cabinet. Clean out debris that has accumulated inside it, which may block the coils. You don’t have to make it spotless. If fins are bent over in spots, try to straighten them enough so more air gets through.
It is important that all of the screws holding the cabinet sections together are tight when you reinstall the cabinet. Even if it is clean, and you do not remove the cabinet, check all of the screws. If they are loose, leaks will draw air in gaps instead of through the coils as designed.
Just as the proper amount of air flow is important through the outdoor coils, it is also important through the indoor coils. With the circuit breaker still switched off, remove the side cover on the indoor unit to expose the evaporator coils and the blower. When you reinstall the cover, make sure to tighten the screws.
A lot of dirt can accumulate on the indoor coils because the coils get damp when the air conditioner is running and dirt sticks to them. The dirt blocks air flow and insulates the coils from the air. Wipe the coils and use the brush attachment on your vacuum cleaner to clean them and the blower as well as possible.
Although you often hear the blower filter should be changed regularly, most people don’t do it. At the beginning of the cooling season, change the filter whether you think it is dirty or not. A dirty filter increases air flow resistance, which reduces efficiency. Check the joints in the ducts for any air leaks. Seal them with aluminum tape or black Gorilla duct tape.