What Actually Happens on A/C Installation Day
A walkthrough of a proper residential changeout, hour by hour — including the steps that separate a good install from a fast one.
A standard residential air conditioning changeout takes six to eight hours. The sequence is protecting the home, recovering refrigerant and removing old equipment, setting the new outdoor unit and indoor coil, brazing and evacuating the line set to 500 microns, charging, then commissioning — measuring static pressure, temperature split, superheat, and subcooling to verify performance.
Before the truck arrives
A good installation starts before install day. The load calculation is done, the equipment is confirmed in stock, the permit is pulled where required, and the scope is in writing — including any duct work, electrical changes, or pad and disconnect replacement.
On your end: clear a path from the driveway to the indoor unit, move vehicles, secure pets in a room that will not be disturbed, and plan for the system to be off most of the day. In summer that matters; in March it does not.
The sequence
- Protection and setup. Floor coverings from the entry to the equipment, drop cloths, and a staging area outside.
- Refrigerant recovery. The old refrigerant is recovered into a tank for proper disposal. Venting it is illegal and, for what it is worth, a reasonable signal about the rest of a company's practices.
- Old equipment out. Outdoor unit disconnected and removed, indoor coil or air handler pulled.
- Line set evaluation. Existing copper is inspected, and if it is being reused it is flushed. On some installs, particularly a refrigerant change, it is replaced.
- New equipment set. New pad, level, correct clearances. Indoor coil fitted and sealed to the plenum.
- Brazing. Connections brazed with nitrogen flowing through the line to prevent internal oxidation — a step that is skipped constantly and causes problems years later.
- Evacuation. Vacuum pulled to 500 microns or below and held, to remove moisture and non-condensables. This takes real time and is the step most often shortchanged.
- Charging. Refrigerant weighed in per the manufacturer specification, then verified by superheat or subcooling.
- Electrical. New disconnect, whip, and correct breaker sizing verified.
- Condensate. Drain and float switch installed and tested.
- Startup and commissioning. The part that separates installations.
Why evacuation matters more than it sounds
Air and moisture inside a refrigerant circuit cause real damage. Moisture reacts with refrigerant oil to form acids that attack windings and metal surfaces from the inside. Non-condensable gases raise head pressure and reduce capacity.
A proper evacuation pulls the system down to 500 microns or lower and confirms it holds — which proves both that the moisture is gone and that the system has no leaks.
It takes time, sometimes an hour or more, and there is no way to see afterward whether it was done. That is precisely why it gets skipped on rushed installations. Ask what micron level was reached and whether a decay test was performed. A good installer will tell you the number without hesitating.
Commissioning: what should be measured
- Static pressure across the air handler, confirming the ductwork can handle the equipment
- Return and supply air temperatures, and the resulting temperature split
- Superheat or subcooling, confirming the charge is correct for the actual conditions
- Amp draw on the compressor and both motors, compared against nameplate
- Airflow verification, ideally room by room
- Condensate drainage and float switch operation
- Thermostat configured for the actual equipment type and staging
The walkthrough at the end
Before the crew leaves, you should be shown where the filter goes and what size it is, how to operate the thermostat, where the outdoor disconnect and the indoor service switch are, and what the maintenance schedule looks like.
You should also receive the model and serial numbers, the warranty registration confirmation or a commitment to send it, the permit documentation if applicable, and the commissioning readings.
If anything is not working the way it should, say so that day. The crew is there, the equipment is fresh, and problems found on install day are vastly easier to resolve than problems found in July.
Red flags during the install
Refrigerant released to atmosphere rather than recovered. A vacuum pump running for only a few minutes. No nitrogen bottle present during brazing. Charge added "by feel" rather than weighed and verified. No instruments used at startup. A crew leaving without giving you any numbers.
None of those guarantee a bad outcome, and a busy day can look chaotic. But collectively they describe an installation optimized for speed rather than longevity, and in this climate the difference shows up in four or five years.
Frequently asked
How long does it take to install a new air conditioner?
Six to eight hours for a straightforward changeout in the same location using existing ductwork. Adding a new line set, relocating equipment, or performing significant duct work can extend it into a second day.
What is evacuation and why does it matter?
Pulling a deep vacuum on the refrigerant circuit — to 500 microns or below — to remove air and moisture before charging. Moisture reacts with refrigerant oil to form acids that damage the system from the inside. It takes time, cannot be verified afterward, and is the step most often shortchanged.
What should I ask for after an HVAC installation?
The commissioning readings in writing — static pressure, temperature split, superheat or subcooling, and amp draws — plus model and serial numbers, warranty registration confirmation, and permit documentation. Those readings are also the baseline for every future service visit.