Commissioning means proving that an installed system works as designed. Pre-commissioning is everything you check before the compressor runs for the first time. Think of it like checking oil, water and tyres before a long drive on the highway.

Problems found now cost a few minutes. The same problems found after start-up can cost a compressor. A dry pump, a closed valve or a reversed phase can cause damage within minutes.

Work in four groups: mechanical, water side, refrigerant side and electrical. Tick each item only after you have seen it yourself, not because someone told you.

Commissioning checklist

Mechanical

• Unit sits level on a firm base or frame, with anti-vibration pads fitted.
• Air clearances around the coil and fan match the installation manual.
• No air short-circuit: discharge air cannot return to the coil inlet.
• Condensate and defrost drain is free and slopes away from the unit.
• All transport brackets and packing inside the unit are removed.

Water side

• Piping is flushed clean before connecting to the heat pump.
• Strainer is fitted on the inlet to the heat pump and its mesh is clean.
• All isolation valves on the heat pump circuit are open.
• Air vents are fitted at high points and the system is fully vented.
• Closed system: cold fill pressure is set (typical 1.5–2.0 bar) and the expansion vessel pre-charge is checked.
• Water side pressure test passed (typical 1.5 × working pressure, held with no drop).
• Water quality is checked: hardness and TDS recorded; softener or treatment fitted where water is hard.
• Circulating pump turns freely and rotates in the correct direction.
• Flow switch is fitted in the correct direction and wired.
• Pipes and fittings outdoors are insulated and UV protected.

Refrigerant side

• Monoblock: standing pressure on the gauges is present (unit not empty).
• Split: nitrogen pressure test passed, vacuum below 500 micron (typical), charge as per manual.
• No oil stains at brazed joints, valves or flare nuts.
• Service valves are fully open (split units) and caps refitted.

Electrical

• Supply voltage at the unit terminals is within ±10% of nameplate (typical).
• Three-phase: voltage imbalance between phases is below 2% (typical).
• Phase sequence is correct (phase rotation meter or controller check).
• Cable size, MCB/MCCB rating and RCCB match the manual.
• Earth is connected and earth continuity is checked.
• Insulation resistance of compressor windings to earth is above 1 MΩ (500 V tester, typical minimum).
• All terminal screws are tightened, including inside the control panel.
• Crankcase heater has been energised for the time stated in the manual (typical 12–24 hours).

Remember

• Never start a heat pump with closed water valves or an unvented circuit.
• Wrong phase sequence can damage a scroll compressor within minutes.
• Measure insulation resistance before first power-up, not after a fault.
• Record every reading; the checklist becomes part of the handover file.