Central Air Conditioners If air conditioners have been installed in properly size and professionally would be performed efficiency for years and with only annually minor routine maintenance they could last longer.if you buy modern energy efficient one with inappropriate installation it could perform almost as poor as older inefficient model.when you are installing a new air conditioner be sure: -Allow appropriate space in front and back of plenum to make a way to access evaporator coil to clean or repair it. -Make sure proper duct air circulation, don't block return or supply registers. -All ducts going through open space like attic and garage must be insulated. -Place condensing unit where noise do not bother you and your neighbour. -Out door units must have enough space all around to circulate air. -Each condensing unit has certain refrigerant volume if more or less would be damaged soon.