Evacuation means removing air and water vapour from the refrigerant circuit with a vacuum pump. Water boils at very low pressure, so a deep vacuum makes moisture boil off and get pumped away. A micron gauge measures vacuum in microns of mercury (1 micron ≈ 0.133 Pa). The manifold's compound gauge is not accurate enough for this.

Evacuation steps

1. Remove Schrader cores with a core tool and use short, large-bore hoses for speed.
2. Connect the micron gauge as far from the pump as possible, ideally at the system.
3. Run a two-stage vacuum pump with fresh oil.
4. Pull down to the target. A common field target is 500 microns or lower (typical; follow the manual).
5. Isolate the pump and do a decay test, typically 10–15 minutes.
6. If the gauge rises and levels off below about 1,000 microns, the system is dry and tight. If it keeps rising steadily, there is a leak. If it rises and stops high, moisture remains: evacuate further.

Charging

• Charge by weight on a digital scale. Do not charge "by pressure" or "by feel of the suction line".
• Many split units are pre-charged for a set pipe length. Add extra charge per metre beyond it, as the manual states.
• Blends such as R410A and R407C must be charged as liquid. R32 is a single refrigerant, but liquid charging is still the normal practice.
• R32 and R290 are flammable (A2L and A3 safety classes). Use tools rated for them, remove ignition sources, and ventilate. R290 needs specific training.
• Record the charge on the unit label and in the commissioning sheet.

Worked example — additional charge

A split unit in Kolkata is pre-charged for 7.5 m of pipe. The actual pipe run is 15 m. The manual says add 20 g per metre (example value) for the liquid line size used.

1. Extra length: 15 − 7.5 = 7.5 m.
2. Extra charge: 7.5 × 20 = 150 g.
3. Weigh in 150 g as liquid, slowly, through the suction service port with the unit running (or as the manual says).

Remember

• Use a micron gauge; pressure test first, then vacuum.
• Target and decay test tell you dry, wet or leaking.
• Charge by weight; blends as liquid.
• Treat R32 and R290 as flammable: right tools, no sparks.