Commissioning, testing and handover of systems
Pre-commissioning and pressure testing
Commissioning starts with verification, not valves: check electrical isolation and rotation, controls wiring, sensor placement, insulation continuity, drains and trap heights, and that the system matches the as-fitted drawings. Pressure test with oxygen-free nitrogen through a regulator, never above the manufacturer's stated test pressure, and record the test pressure and duration.
Evacuation and dehydration
Triple evacuation using a good vacuum pump and a micron gauge (not manifold gauges) removes moisture and non-condensables. The standing vacuum test is the real test: isolate the pump and confirm the vacuum holds. A common benchmark is below 500 microns (about 67 Pa), holding with no significant rise over the test period. Then charge by weight, from a calibrated scale, and record the amount.
Performance and handover
Run the system at, or corrected to, design conditions and record: suction and discharge pressures, evaporating and condensing temperatures, superheat, subcooling, currents, air/water flows and temperatures, sound and vibration, and all safety interlocks and alarms proven. Hand over the O&M manuals, as-fitted drawings, commissioning records, refrigerant records and training, and obtain signed acceptance.
Worked example
Suction line temperature measured 8 °C with a saturated evaporating temperature of 2 °C gives 6 K superheat - comfortably within a typical 5–8 K target for a DX system. If superheat were 0 K, suspect floodback or an over-fed/incorrectly set expansion valve before blaming the charge.
Traps
Using manifold gauges for vacuum; failing to prove interlocks; commissioning in weather that does not match design without correcting the readings; charging by guesswork instead of weight.