Maintenance is preventive, not magic
Routine care can catch wear, airflow issues, drainage concerns, and other developing problems, but it cannot guarantee that equipment will never fail.
Homeowner tasks
Keep accessible filters on an appropriate replacement schedule, keep vents and outdoor equipment areas unobstructed, and pay attention to changes in sound, cycling, or comfort.
Professional maintenance
A professional visit can inspect operation, electrical components, safety controls, drainage, temperature performance, and other system-specific items that are not appropriate DIY tasks.
Safety note: If you smell gas, see smoke or fire, suspect carbon monoxide, or believe there is an immediate safety danger, leave the area as appropriate and contact the relevant emergency or utility service. Do not treat an active safety emergency as a routine HVAC appointment.