FieldBench
How To
Charge18 min · 6 steps

Charge an R-32 air conditioner

Weigh it. Stabilize it. Do not treat R-32 like a 410A top-off. A2L rules are the job, not a footnote.

Before you start

  • R-32 is A2L — mildly flammable. No open flame, no screwdriver-spark on a capacitor, no smoking at the unit.
  • R-32 is not a drop-in for R-410A. Do not put it in a 410A chassis. AHRI: do not retrofit across flammability classes.
  • Stay under the OEM maximum charge. Mitigation (sensor / ventilation blower) is part of the charge limit on some pairs.
  • EPA 608: recover. Do not vent. Silver cylinder with a red band is the A2L bottle — confirm the stamp is R-32, not R-454B.

On the truck

  • Charging scale under the cylinder — every time
  • A2L-rated manifold / hoses / leak detector
  • Core-removal tools
  • A2L-rated recovery machine if you have to take gas back out
  • Psychrometer + clamp thermistors (insulated on bare copper)
  • OEM charging chart / nameplate for THIS outdoor

Steps

  1. 1 Read the outdoor nameplate, not your last 410A job

    Confirm refrigerant R-32, factory charge weight, line-set adder, metering device (TXV vs EEV vs piston), and any A2L mitigation note. R-32 uses POE-46. R-410A / R-454B use POE-32. Wrong oil is a compressor call later.

    Expect: Plate says R-32. Cylinder stamp matches. Indoor coil / lines are rated for this pair.

    If it fails: Stop. Wrong gas, a 410A indoor, or a leftover 454B bottle is a recover-and-start-over, not a trim.

  2. 2 Airflow and the coil before any gas moves

    Filter, blower speed / communicating CFM, indoor coil clean, outdoor coil clean, OD fan running the right way. A dirty indoor coil will fake a starve. Ice means thaw first — never charge a frozen coil.

    Expect: Indoor air moving. No ice. Outdoor rejecting heat.

    If it fails: Fix airflow. Charge last.

  3. 3 Leak-check, then evacuate — required on A2L, not optional

    Nitrogen standing test on an opened system, then pull a deep vacuum. Kalos / HVACR School field target on a new system: below 300 microns, decay not above 500 microns in 10 minutes. In-service: 500 microns, decay not above 1000 in 10 minutes. OEM spec wins if it is tighter.

    Expect: Decay holds. Micron gauge is on the system (CRT side port), not on the pump.

    If it fails: Continuous rise is a leak. Sharp rise that flattens is moisture — more pump time or a nitrogen sweep, not more gas.

  4. 4 Weigh in the nameplate + line-set adder with the system off

    Scale under the cylinder. Weigh the factory charge plus the OEM adder for extra liquid-line feet. R-32 is a single-component gas — follow the OEM path (usually liquid into the liquid line through a restrictor, or the published vapor method). Do not ‘guess 6 lb because the last 3-ton was 6 lb.’

    Expect: Scale reads the calculated weight. Cylinder labeled R-32. Cores still out or tools still on.

    If it fails: If you cannot get the published weight in, find the restriction or the leak. Do not start the compressor in a vacuum.

  5. 5 Start, then wait — do not trickle every 30 seconds

    Run in cool. Indoor WB and outdoor DB in the shade. HVACR School: let pressures and line temps stabilize about 10 minutes before you add more. R-454B cousins can wander for much longer (field reports up to an hour) — do not chase a moving SC with more gas.

    Expect: Stable SH and SC vs the OEM chart for this metering device after a real wait.

    If it fails: High SH + low SC = starve / restriction / undercharge. High SC + high head = overcharge or non-condensables. Do not add gas because suction ‘looks low.’

  6. 6 Trim on the chart, then write the weight

    TXV / EEV: subcooling is the charge knob; superheat is valve health. Piston: superheat vs the OEM WB/DB chart. Liquid-only on zeotropes (454B). On R-32, still weigh every ounce you add after the weigh-in. Tag the cylinder and the ticket with job number and pounds.

    Expect: Final charged weight on the ticket. SH/SC in the OEM window. No A2L alarm.

    If it fails: If SC will not settle, recover to the calculated weight and start over. Do not leave an overcharge ‘to be safe.’

Field notes

  • R-32 discharge temperature runs higher than 410A. High head with a clean coil and a correct weight is not automatically ‘add gas.’
  • Total charge changes when mitigation is in play — the I/O for that pair is law.
  • Always use a proper capacitor discharger on A2L equipment. A screwdriver spark is an ignition source.
  • Open the Charge calculator in FieldBench for a PT sanity check. The outdoor charging chart still wins.

Related

Sources

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