If your air conditioner is installed correctly, or if major installation problems are found and fixed, it will perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models.

Be sure that your contractor performs the following procedures when installing a new central air conditioning system:

• allows adequate indoor space for the installation, maintenance, and repair of the new system, and installs an access door in the furnace or duct to provide a way to clean the evaporator coil.
• uses a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA) Manual D.
• ensures there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner.
• installs duct work within the conditioned space, not in the attic, wherever possible.
• seals all ducts with duct mastic and heavily insulates attic ducts.
• locates the condensing unit where its noise will not keep you or your neighbors awake at night, if possible.
• places the condensing unit in a shady spot, if possible, which can reduce your air conditioning costs by 1% to 2%.
• verifies that the newly installed air conditioner has the exact refrigerant charge and air flow rate specified by the manufacturer.
• locates the thermostat away from heat sources, such as windows, or supply registers.

If you are replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit. (The air conditioner's efficiency will likely not improve if the existing evaporator coil is left in place; in fact, the old coil could cause the new compressor to fail prematurely.)

If you install a new room air conditioner, try to:

• locate the air conditioner in a window or wall area near the center of the room and on the shadiest side of the house.
• minimize air leakage by fitting the room air conditioner snugly into its opening and sealing gaps with a foam weatherstripping material.

Paying attention to your air conditioning system saves you money and reduces environmental pollution. Notice whether your existing system is running properly, and maintain it regularly. Or, if you need to purchase a new air conditioner, be sure it is sized and installed correctly and has a good EER or SEER rating.