The AC installation process for a full central air replacement usually takes 8 to 14 hours, while swapping only the outdoor unit takes 4 to 8 hours, according to Carrier. On installation day, the crew removes the old equipment, sets the new outdoor unit and indoor coil, connects the refrigerant lines and wiring, pulls a vacuum, charges the system and then tests it before handing it over.
Below, we walk through each step of the AC installation process, explain what a good crew checks before leaving and show how you can prepare. Information checked on November 4, 2026.
How long the AC installation process takes
| Job | Typical time | Source |
|---|---|---|
| Outdoor unit only | 4–8 hours | Carrier (Oct. 27, 2026) |
| Full split system (outdoor and indoor units) | 8–14 hours | Carrier (Oct. 27, 2026) |
| New HVAC system with existing ducts | 1–2 days | HomeGuide (Aug. 27, 2025) |
| New HVAC system with new ductwork | 3–5 days | HomeGuide (Aug. 27, 2025) |
Before installation day
- Sizing: first, make sure the contractor sized the system from your home’s actual characteristics, not a rule of thumb, as ENERGY STAR recommends.
- Permit: most municipalities require a permit for AC replacement, Fixr says, and HomeGuide notes that contractors typically include permit fees in the estimate.
- Matched equipment: also confirm the refrigerant type and that the indoor coil matches the outdoor unit.
- Line set: ask whether the existing refrigerant lines will be reused. North Carolina’s fire marshal guidance says they may stay if they meet the manufacturer’s requirements.
- Access: finally, clear a path to the outdoor unit, the attic or closet and the electrical panel.
AC installation process: step by step
- Shutoff and refrigerant recovery. The crew turns off power and recovers the refrigerant from the old system; Angi notes that contractors handle refrigerant recovery during removal.
- Removal. Next, they disconnect and remove the old outdoor unit and indoor coil.
- Setting the new equipment. The new outdoor unit goes on a level pad or bracket, while the matched indoor coil sits on the furnace or air handler.
- Brazing the lines. Building Science Corporation (BSC) recommends flowing dry nitrogen through the lines while brazing to prevent carbon deposits, and installing a filter-drier in the liquid line.
- Pressure test. Then the crew pressurizes the lines and coil with dry nitrogen, 125 to 150 psi in BSC’s procedure, and checks for leaks.
- Evacuation. After that, a vacuum pump pulls the system down to 300 microns or lower; it should then hold below 700 microns for at least 10 minutes, according to BSC.
- Electrical and drain. Technicians connect the power, the thermostat wiring and the condensate drain line.
- Charging. The technician releases the refrigerant from the condenser, adjusts the charge by weight for the actual line length and then fine-tunes it with superheat or subcooling readings.
- Startup and airflow check. The system runs for at least 15 minutes while the crew checks the temperature drop across the coil and the duct static pressures, BSC says.
- Walk-through. Finally, they clean up, set up the thermostat and explain the warranty and the inspection.
Why the details of the AC installation process matter
Small mistakes can cost real efficiency. For example, BSC estimates that if the refrigerant charge is off by 20%, performance drops about 5% on a system with a thermostatic expansion valve (TXV) and 15% to 20% with a fixed metering device. Similarly, ENERGY STAR says airflow problems can reduce a system’s efficiency by up to 15%.
In addition, newer A2L refrigerant systems may include a refrigerant leak detection system. According to North Carolina’s fire marshal guidance, some manufacturers require the installer to connect it to the furnace fan.
What to check before the crew leaves
- Ask whether they ran a nitrogen pressure test and a vacuum decay test, and what micron reading the system held.
- Confirm that the charge was set by weight and checked with superheat or subcooling.
- Ask for the airflow or static pressure readings.
- Make sure the condensate drain works and the thermostat is set up correctly.
- Also get the model and serial numbers for warranty registration, plus the permit inspection date.
After installation
Afterward, inspect, clean or change the filter once a month and book a check-up every spring, as ENERGY STAR recommends. For more help planning a new system, see our AC replacement cost guide, our guide on what size AC you need and the best time of year to replace your AC.
AC installation FAQ
Do I need to be home during AC installation?
Usually at the start and for the final walk-through, since the crew needs access to the indoor unit and the thermostat. Still, ask your contractor exactly what they need from you.
Does AC installation require a permit?
In most places, yes. Fixr says most municipalities require permits for mechanical changes, including AC replacement, and HomeGuide puts replacement permits at $100 to $250.
Can the old line set be reused?
Sometimes. North Carolina’s fire marshal guidance says existing line sets may remain if they meet the manufacturer’s requirements; otherwise, you’ll need new lines.
Sources and review
Sources: Carrier, air conditioner prices in 2026 (October 27, 2026); HomeGuide, new HVAC system cost (August 27, 2025); HomeGuide, AC replacement cost (July 25, 2025); Building Science Corporation, Info-607: refrigeration system installation and startup procedures (May 10, 2010); ENERGY STAR, HVAC quality installation; ENERGY STAR, maintenance checklist; North Carolina Office of State Fire Marshal, A2L partial replacement interpretation (June 6, 2025); Angi, new furnace and AC cost (2026 data); Fixr, AC installation cost (January 28, 2026). All checked on November 4, 2026.
Written by: HVAC Switch. Last updated: November 4, 2026. Read our editorial policy to learn how we research prices, or contact us if you spot an error.