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A contractor called out to repair a central AC unit in Rock County has to work through two different questions before any part gets quoted or replaced. 149 severe weather events were recorded in Rock County, Wisconsin between 2015 and 2024. At that rate, wear from repeated severe weather events is a real factor in what a compressor, capacitor, or contactor looks like when opened up, and a contractor who skips that reading risks misidentifying the failure. Age and maintenance history still matter. So does knowing how much of the damage was driven by load the system absorbed from the outside rather than by ordinary mechanical decline inside it.
Ductwork and wiring in a house this old were put in long before the system now running in it, but for repair work, that gap is not where the job stalls. Half the homes in Rock County, Wisconsin were built in 1970 or earlier (2020-2024 ACS 5-year). A system installed into stock that old has been drawing on a parts supply that narrows every year. When a compressor or control board fails, the question a contractor answers before anything else is whether the replacement part still exists as a stocked item or has to be sourced as obsolete. That answer determines whether the repair is a day's work or a decision about replacement.
The Parts of a Central AC a Contractor Checks First
The outdoor condenser unit sits outside the house, usually on a concrete pad at ground level, and it is where heat from inside the house gets released. The indoor air handler or furnace-mounted evaporator coil sits inside, most often in a basement, closet, or utility space, and it is where that heat gets picked up. Both are early stops when a contractor is tracing a problem.
The refrigerant lines run between those two units, and the expansion valve controls how refrigerant moves through the evaporator coil. The thermostat on the wall and the electrical components inside each cabinet, including capacitors and contactors, round out what a contractor works through when the system is not cooling the way it should.
The drawing shows the general layout of a central AC system, and a licensed contractor determines which components apply and what condition they are in for your specific house.
Find a contractor in Rock CountyRock County by the numbers
149 severe weather events were recorded in Rock County, Wisconsin 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 Rock County, Wisconsin were built in 1970 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesRock County, Wisconsin holds 71,109 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 71.2% of the occupied homes in Rock County, Wisconsin (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesCodes & Standards Behind Central AC Repair in Rock County, Wisconsin10 sourced rules and standards
What Happens When the Contractor Arrives
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.
What Rock County and Wisconsin Require for HVAC Repair
A Wisconsin business that employs a certified HVAC qualifier is a certified HVAC business, and no city or county may require it to hold a local certification or licence on top of that.
Wisconsin requires a state HVAC contractor registration: no person or business may install or service heating, ventilating or air conditioning equipment, or offer to, without one.
Severe Weather Events in Rock County, Year by Year
Extreme weather puts mechanical stress on AC equipment: hard runs during heat, power fluctuations from storms, and pressure swings that wear components faster than steady conditions would. How much of that load a system carries depends on what the local climate actually delivers, which is why the record for Rock County belongs on a page about keeping that equipment running.
149 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.