A service is maintenance and a performance check in one visit. Before anything is opened, the technician runs the system and measures the air going in against the air coming out, which gives a number to compare once the work is done.
Indoor unit: filters washed and dried, coil inspected and its front face cleaned, barrel fan checked, drain tray and line flushed until water runs freely, and the remote settings checked, because a unit stuck on dry or fan mode looks exactly like a faulty one. Outdoor unit: debris cleared from the coil fins, fan and clearance checked. A condenser boxed in by a hedge breathes its own hot air on a 38-degree day. Electrical and refrigerant: connections, isolator, capacitor and fan motors checked, and refrigerant pressures checked by a licensed refrigeration technician when the symptoms call for it. Odd pressures point to a leak or an airflow problem long before the cooling stops. Our guide to what a split system service includes has each step in detail.