Air conditioning units from 1- to 4-ton sizes can be purchased at Lowe's, The Home Depot, Amazon.com and local distributors of specific brands, such as Amana, Lennox, Carrier and Trane. The Home Depot and Lowe's offer onsite consultation and installation services, as do most distributors, but Amazon.com does not.
Most air-conditioner units and installation services come with warranties of varying length and coverage. House size, number of windows, quality of insulation and other appliances in use can affect the size of the air conditioner needed to properly cool the home. The energy-efficiency rating of the unit also impacts the cost of operating the system.