Start-Up, Commissioning, and Performance Verification
This domain tests pre-start checks, commissioning measurements, and performance verification. Expect questions on evacuation, charging, airflow, temperature split, electrical readings, auxiliary heat, defrost testing, and documentation.
Core rules and concepts
- Before start-up, verify torque on electrical lugs, correct breaker and disconnect, control wiring, valve positions, condensate drainage, and that the crankcase heater has been energized as required.
- Leak test and evacuate before charging. Confirm the vacuum holds and that the system is charged by weight or by the manufacturer’s subcooling/superheat method.
- Verify airflow before final charge adjustment. Measure TESP, filter condition, blower speed, and cfm.
- Performance checks include return and supply temperature split, suction and liquid pressures, superheat, subcooling, compressor amp draw, voltage, and outdoor fan operation.
- Test auxiliary heat, emergency heat, defrost initiation and termination, and low-ambient lockout controls.
- Record all readings on a commissioning report.
Worked example
A 3-ton system has a return-air temperature of 75°F and a supply-air temperature of 95°F, so ΔT = 20°F. At 1,200 cfm the sensible capacity is approximately 1.08 × 1,200 × 20 = 25,920 Btu/h. If the expanded rating at these conditions is 30,000 Btu/h sensible, the measured performance is low. Check airflow, charge, and duct losses before condemning the equipment. A low ΔT can mean high airflow or low charge; a high ΔT can mean low airflow.
Traps that cost marks
Adjusting charge before verifying airflow; using air temperature split as the only charging method; skipping the defrost test; failing to verify auxiliary and emergency heat; and leaving no commissioning record.