The cost of replacing an air conditioning (AC) unit varies depending on several factors such as the type of system, its size, energy efficiency, and installation complexity. On average, replacing a central air conditioning system ranges from $3,500 to $7,500, including installation. Smaller units, like ductless mini-split systems, typically cost between $2,000 and $5,000, while portable and window units are more affordable, ranging from $150 to $800. Additional costs may include labor fees, ductwork repairs, permits, and thermostat upgrades, which can further impact the overall price. High-efficiency units may have a higher upfront cost but provide long-term energy savings.