A typical service call includes checking the capacitor, contactor, and fan motor, cleaning or inspecting the outdoor coil, measuring refrigerant pressures, and testing airflow and the condensate drain. Refrigerant work requires the proper federal certification and, on larger systems, a Massachusetts refrigeration license, so it isn't a homeowner job.
If you're replacing a system, Carver's Building Department lists major appliances among jobs needing an electrical permit, and ductwork changes may need a sheet metal permit. Applications go in on paper, and the wiring inspector works Monday, Wednesday, and Friday.
In a mobile home park, a new condenser pad or line set is outdoor work, and the town advises checking whether the park association must approve it first.