Sacramento's climate calls for twice-a-year HVAC service. Spring service — ideally March or April — catches AC issues before the first triple-digit heat wave, when every technician in the region is already booked. Fall service — September or October — catches furnace issues before the first significant cold snap, when a furnace that's sat idle all summer fires up for the first time.
A proper AC tune-up covers capacitor testing, contactor inspection, refrigerant-charge verification, condenser-coil cleaning, blower-motor amperage, temperature split across the evaporator, and thermostat calibration. A furnace tune-up covers igniter or pilot assembly, flame-sensor cleaning, gas-valve pressure, burner inspection, heat-exchanger visual inspection, blower amperage, and combustion analysis.
Most failures during a Sacramento heat wave trace back to items that would have been caught during a spring tune-up — marginal capacitors, dirty condensers, low refrigerant charge. The $150 to $250 you spend on twice-a-year service pays back many times over in avoided emergency calls and extended equipment life. A well-maintained heat-pump or central-AC system routinely lasts 18 to 22 years in this climate; a neglected one fails at 10 to 12.
Filters are a separate conversation: change at least every 90 days during cooling season, every 60 days if you have pets, every 30 days during significant wildfire-smoke events.