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Sizing a central AC system for this county starts with an honest count of what the compressor is actually asked to do each year. Homes in Harrison County, MO run cooling about three months a year, from June through August. The compressor, the condenser fan, and the contactor all sit idle through a long stretch of the calendar, and that idle time does not protect them. Faults that develop during the off-season go unfound until June, and a unit that is undersized shows its weakness exactly when outdoor temperatures peak and the system has no reserve left to hide behind.
Ductwork laid for equipment that no longer exists in these houses is often what decides how an installation job goes. Half the homes in Harrison County, Missouri were built in 1966 or earlier (2020-2024 ACS 5-year). When the ducts were designed around a system that has since been replaced, the routing, the sizing, and the return-air paths may not carry what a current central AC unit needs. A contractor installing new equipment here opens those runs and measures what they actually deliver, because a duct layout that looks complete from the outside can still starve a new system of airflow. The electrical service gets the same look, since the panel that served the original equipment may not match the draw of a modern unit.
What a Central AC System Includes
The outdoor unit sits on a concrete pad beside the house and holds the compressor and condenser coil. Inside, the air handler or furnace cabinet stands in a utility space, basement, or closet and carries the evaporator coil, which is the piece that pulls heat from the air moving through it. Together these two units form the refrigerant circuit at the heart of a central system.
A copper refrigerant line set runs between the two units, connecting the indoor and outdoor sides and carrying refrigerant in both directions. A thermostat mounts on an interior wall and serves as the control point for the whole system, telling it when to run and when to stop.
The drawing shows the typical layout of these pieces, and a licensed contractor determines exactly how they come together in your home.
Get matched in Harrison CountyHarrison County, Missouri, by the numbers
88 severe weather events were recorded in Harrison County, Missouri 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 Harrison County, Missouri were built in 1966 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesHarrison County, Missouri holds 4,008 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 71.4% of the occupied homes in Harrison County, Missouri (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesCodes & Standards Governing Central AC Installation in Harrison County, Missouri8 sourced rules and standards
What happens once a contractor shows up
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.
Severe Weather Events in Harrison County
Weather puts a cumulative load on central AC equipment, and that load is shaped by local conditions. What hits Harrison County shapes what the equipment here has to handle, which is why installation decisions are a local question.
88 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.