FieldBench
How To
Charge12 min · 3 steps

Weigh in a new split (any refrigerant)

Nameplate plus liquid-line feet. The charging chart is a trim, not a substitute for the scale.

Before you start

  • Match the cylinder to the nameplate. R-32, R-454B, and R-410A are different jobs.
  • A2L: max charge / mitigation limits still apply on a ‘standard’ 15-foot line set if the indoor is in a small space.
  • Do not start the compressor to ‘pull the charge in’ from a vacuum. Weigh in with the system off, then start.

On the truck

  • Charging scale
  • OEM I/O: factory charge and oz-per-foot adder
  • Core tools, vacuum already passed
  • Thermistors and the Charge screen for SH/SC trim

Steps

  1. 1 Calculate before you open the bottle

    Factory charge on the outdoor plate is for a stated line-set length (often 15 ft — read it). Extra liquid-line feet × the OEM oz/ft. Some brands subtract for a short set. Write the target pounds on the ticket before the valve opens.

    Expect: A target weight, not a feeling.

    If it fails: No adder on the plate → open the I/O or the install book attached to this model in FieldBench.

  2. 2 Weigh in liquid with the system off

    Passed decay. Cores out or tools on. Liquid from the cylinder into the liquid line (restrictor / liquid valve per OEM). Zeotropes (410A, 454B, 407C): liquid only. R-32: OEM path. Watch the scale to the ounce.

    Expect: Target weight in the system. Cylinder closed.

    If it fails: Weight will not move → a closed king valve or a frozen hose. Do not start the compressor to force it.

  3. 3 Run and trim on the device, not on suction pressure

    Cool call, 10+ minutes (longer on 454B). TXV: hit published SC. Piston: published SH from indoor WB + outdoor DB. High SH + low SC is still a starve. High SC + high head is still overcharge or non-condensables. Put the final charged weight on the ticket.

    Expect: SH/SC in the OEM window. Final weight written.

    If it fails: If you added more than a few ounces of trim, you either missed the adder or you have a leak / restriction. Recover and weigh the whole charge — do not keep topping.

Field notes

  • HVACR School: if you do not use a scale every time you add or remove refrigerant, start today.
  • A piston system charged by ‘beer-can cold’ is how you bury a restriction.

Related

Sources

Practice distilled from public HVACR School and AC Service Tech material. OEM I/O and EPA 608 still win.