Evacuation & Charging

Pull a deep vacuum, confirm a decay test, weigh in the charge, then verify superheat/subcool.

Approx. 120 min

Before you start

•Line set and all joints have already passed a pressure/leak test — never pull a vacuum to find leaks.
•Vacuum pump oil is fresh and the micron gauge is at the system (not at the pump), with core removal tools for speed.
•Nameplate charge / metering-device type and the target superheat or subcool window are known.

Tools & materials

2-stage vacuum pump (fresh oil) · Micron (vacuum) gauge · Large-bore hoses + core removal tools · Accurate charging scale + refrigerant · Digital manifold + pipe clamp temp probes

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Evacuate

Pull the system into a deep vacuum
Connect with large-bore hoses on both sides (remove the cores) and run the pump down. A deep vacuum boils off moisture and non-condensables; restrictive hoses make this take forever.
Target: Pull below 500 microns
Isolate and run a decay (rise) test
Valve off the pump and watch the micron gauge. A vacuum that rises and stabilizes low usually means residual moisture; one that climbs without leveling means a leak.
Target: Holds below 500 microns with <500 micron rise in 1 minute (rise then stabilizes = dry; keeps rising = leak)
⚠ Don't use the system compressor to pull a vacuum, and never start a compressor under vacuum — it can arc/short the windings.

Charge

Weigh in the nameplate charge
Break the vacuum into the high side with liquid (off the scale) to the nameplate charge, adjusting for line-set length per the maker's table. Weighing in is the most accurate starting point.
Target: Nameplate factory charge + maker's per-foot adjustment for line set over the base length
⚠ Charge liquid into the HIGH side only. Liquid into the suction port can slug and damage the compressor.

Verify the charge

Verify by the right method for the metering device
On a fixed-orifice/piston system use the superheat method; on a TXV/EEV system use the subcooling method. Let the system run and stabilize before trusting readings.
Target: TXV → subcool to nameplate (often ~8–12°F); piston → target superheat off a charging chart
Confirm operating readings and split
With the charge dialed in, confirm suction/head pressures, compressor amps vs RLA, and the indoor temperature split are all in range before you leave.
Target: Supply/return ΔT ~16–22°F; amps ≤ nameplate RLA; superheat/subcool in window