A tune-up should leave you with numbers, not a sticker. Here is the list our technicians work from, in the order they do it.
Cooling side
- Refrigerant charge by superheat and subcooling, written on the report
- Capacitor microfarads against the label (the single most common summer failure)
- Contactor pitting, compressor and fan amp draw
- Condenser coil washed, fins straightened
- Condensate drain cleared and treated, overflow switch tested
- Supply/return temperature split
- Static pressure across the filter and the coil
Heating side
- Combustion analysis: CO, O2, stack temperature
- Heat exchanger inspection with a camera
- Gas pressure at the manifold
- Igniter and flame sensor resistance
- Blower wheel cleanliness and motor amps
- Flue and condensate path
The two things cheap tune-ups skip
The combustion test and the charge measurement. Both take fifteen minutes and both need instruments that cost real money. If a visit does not produce those readings, it was a filter change with a handshake.