A central air replacement runs in a fixed order, and the handoffs between steps are where most gaps show up. Walk the order once before the work starts so you know what each step should leave behind. Plan the job in the weeks before cooling weather, so a slow start does not leave you without cooling when the first warm stretch arrives.
Before the crew arrives
Confirm the model, the matched indoor coil, and whether a duct check is in the scope. Clear the path from the driveway or entry to the outdoor pad and the indoor unit. Mark where the disconnect and the thermostat wire run. Ask who will pull any required permit and who will meet the inspector.
Removal and setting
The old outdoor unit comes out, and refrigerant is recovered from it before the lines are disconnected. Ask who handles that step and confirm it is done under the rules that apply where you live. The new outdoor unit is set on the pad, the lines are run and sealed, and the electrical connections are made.
Controls and charge
The thermostat wiring is checked against the new unit's requirements. The system is charged with refrigerant to the manufacturer's specification. Ask the installer to show you the charge reading and the airflow check, rather than only confirming that they were done.
The handoff
Before the crew leaves, run a full cooling cycle. Check that the air at the supply registers feels cool, that the indoor unit drains properly, and that the outdoor unit runs level and quietly. Ask for the model and serial record, the startup sheet, and the written scope as finished. Keep those papers together in one place.
The first real cooling day
Run the system through its first warm stretch and note how long it runs, whether the rooms reach the set point, and whether anything seems unusual. Call the installer with specific observations rather than a general complaint. For planning, the central air conditioner service life and when to plan page explains how the install year turns into a planning date.