Upgrading Existing Air Conditioners
The compressor units of most air conditioners have an average lifetime of only 10 to 12 years. By carefully following proper maintenance procedures, a quality model may hold up 20 years, but don’t expect the kind of lifetime you get with boilers and furnaces.
Operation and Maintenance
Using natural or forced ventilation at night, while keeping the house closed up tight during hot days, is less expensive than operating your air conditioner (see “Reducing the Need for Air Conditioning,” above). Use air conditioning only when ventilation is inadequate. Don’t cool unoccupied rooms, but don’t shut off too many registers with a central system either, or the increased system pressure may harm the compressor. If your room air conditioner has an outside air option, use it sparingly. It is far more economical to recirculate and cool the indoor air than to cool the hot outdoor air to comfortable temperatures. Always keep all doors and windows closed when operating an air conditioner. Do not operate a whole-house fan or window fans while using the air conditioner.
You will probably be comfortable with the thermostat set at about 78°F, but ceiling fans can increase your comfort range. You will save 3–5% on air conditioning costs for each degree that you raise the thermostat. You can also increase comfort at warmer temperatures by reducing humidity; use a bathroom exhaust fan when you shower, run your dishwasher during the cooler evening or early morning hours, don’t dry firewood in your basement, and don’t vent your clothes dryer inside. And don’t forget to set the temperature back (to a warmer temperature) when you leave the house. Rather than relying on your memory and manually resetting the thermostat, consider installing a programmable thermostat. (See the programmable thermostat section in heating/maintenance.)
Air conditioners and heat pumps need regular maintenance in order to perform at peak efficiency. Clean the air filters on room air conditioners monthly. They should never be allowed to get dirty enough to impede airflow, as this could cause damage to the unit. The condenser should be cleaned by a professional every other year, or even yearly in dusty locations.
Central air conditioning units should be inspected, cleaned, and tuned by a professional once every two to three years. This will extend the life of the unit and reduce electricity consumption. Check with your service technician about the proper maintenance schedule for your unit.
During service of your unit, its refrigerant may need recharging. It is important that it is charged correctly. A pre-2006 system that is 20% undercharged can operate at 20% lower efficiency, and field studies show that the majority of older central air conditioners are undercharged enough to affect performance somewhat. However, an overcharged system not only reduces operating efficiency, it can cause damage to the unit and reduce the lifetime of the system. Also, because refrigerants damage the ozone layer, federal law requires that the refrigerant be recovered and recycled.
The service technician should also measure airflow over the indoor coil. Recent studies show that inadequate airflow is a common problem, and average airflow rates tend to degrade over time due to poor maintenance. Correction of airflow rates can improve efficiency by 5–10%.
Even if an air conditioner or heat pump is installed and maintained with adequate airflow and the appropriate level of refrigerant, the unit will not operate efficiently if the duct system is in poor condition. Duct sealing can reduce cooling energy use by 10–15%. (See “Modifications by Heating Service Technicians” in Heating for more on duct sealing.) Power to a central unit should be shut off when the cooling season ends; otherwise the heating elements in the unit could consume energy all winter long. Flip the circuit breaker to turn it off if the unit doesn’t have a separate switch. Turn the power back on at least one day before starting up the unit in order to prevent damage to the compressor.