A common time to book one is February through April, before the first sustained stretch of very hot days exposes marginal components at once.
Tune-up versus maintenance
The terms overlap, and providers may use them differently. In practice, a tune-up often emphasizes testing and adjustment for the coming season — charge, airflow, electrical values, thermostat behavior — while a fuller maintenance visit may add deeper cleaning of coils, blower wheel and drain components. Both matter; if you can only schedule one thing before summer, a tune-up is a reasonable choice.
Measurements commonly taken during a tune-up
- Supply and return air temperature split across the evaporator coil
- Suction and liquid line pressures with superheat and subcooling calculations
- Total external static pressure to detect duct and filter restriction
- Capacitor capacitance versus nameplate rating
- Compressor, condenser fan and blower amp draw under load
- Line voltage and low-voltage control readings
- Condensate flow and safety switch function
- Thermostat cycle rate, differential and calibration
Adjustments that may follow the measurements
Readings outside spec may be corrected where practical: blower speed taps set to deliver proper airflow per ton, charge corrected when superheat and subcooling indicate a genuine imbalance, loose electrical connections tightened, drain lines flushed and treated, and thermostat settings adjusted with humidity control in mind as well as temperature.
Where a component tests marginal — a capacitor reading below nameplate, a contactor with visible pitting — you should receive a clear recommendation and an estimated cost so you can decide before summer rather than face a surprise later.