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Sizing a central AC unit for a Pima County home starts with what the compressor is actually being asked to carry across the year. Homes in Pima County, AZ run cooling about six months a year, from May through October. A compressor that runs through those months cycles its contactor, its motor windings, and its refrigerant circuit far more than a unit sitting in a milder climate would. Undersizing by even a small margin means the compressor runs longer each cycle to keep up, and that added runtime lands on parts that already have little idle time. A contractor has to run a full load calculation before quoting, because a box swapped in at the same tonnage as the old one may repeat the same mistake.
Existing ductwork is what shapes an installation job here, and much of it was designed around equipment long since gone. Half the homes in Pima County, Arizona were built in 1986 or earlier (2020-2024 ACS 5-year). A contractor sizing a new central AC unit has to determine whether the runs, returns, and connections already in the house will carry what the new system moves, and whether the electrical service will support the load. Those are physical questions with answers that vary house to house, which is why the quote follows the inspection.
What a Central AC System Includes
The indoor air handler sits inside the house, usually in a utility closet, attic, or basement, and it circulates conditioned air through the home. The outdoor condenser unit sits on a pad beside the house and holds the compressor and condenser coil. These two units are what a contractor installs as the core of the system.
A refrigerant line set runs between the indoor and outdoor units, carrying refrigerant back and forth through insulated copper tubing. The thermostat mounts on an interior wall and gives the homeowner control over when the system runs and at what temperature setting.
The drawing here shows a typical central AC layout, and a licensed contractor determines exactly what applies to this house.
Get matched in Pima CountyPima County, by the numbers
405 severe weather events were recorded in Pima County, Arizona between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.Half the homes in Pima County, Arizona were built in 1986 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesPima County, Arizona holds 479,939 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 65.2% of the occupied homes in Pima County, Arizona (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesRules & Standards for Central AC Installation in Pima County, Arizona9 sourced rules and standards
What the installation actually looks like
Split-system central air conditioners rated below 45,000 Btu/h manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Split-system central air conditioners rated at or above 45,000 Btu/h manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Split-system central air conditioners manufactured between January 1, 2015 and December 31, 2022 had to meet 13 SEER, the metric that preceded SEER2.
Single-package central air conditioners manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Space-constrained central air conditioners manufactured on or after January 1, 2023 must meet a federal minimum of 11.7 SEER2.
Federal efficiency standards for split-system central air conditioners and heat pumps are set on each certified combination of outdoor unit and indoor coil rather than on the outdoor unit alone.
Residential and light commercial air conditioning and heat pump systems assembled in the field, including mini-splits and unitary systems, may not be installed on or after January 1, 2025 using a refrigerant with a global warming potential above 700.
A field-assembled system whose specified components were all manufactured or imported before January 1, 2025 carries no installation compliance date under the refrigerant restrictions and may still be installed.
Licensing and Legal Requirements in Pima County, Arizona
Arizona requires a contractor licence in good standing: it is unlawful to engage in the business of contracting, to bid, or to act or hold yourself out as a contractor without one.
Severe Weather Events in Pima County
Weather conditions drive how hard cooling equipment works and how often it runs. A system sized and installed for what Pima County actually sees will hold up far better than one built for an average that does not exist here.
405 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.