Field reference

The numbers you actually
use on the job.

Charging targets, what the split is telling you, A2L handling, and the two electrical checks that settle a no-cool call. Print the card, laminate it, put it on the visor.

Download the card
Free, and no form. Two sides, 4 by 6 inches, print ready.

Which method goes with which metering device

Charge to the metric the device actually controls. The nameplate wins over anything on this page.

TXV or EEV
Charge to subcooling
Target 8–12°F, aim for 10. Then sanity check superheat: it should land 8–15°F.
Fixed orifice
Charge to superheat
Off the target superheat chart: indoor wet bulb plus outdoor dry bulb. Never one fixed number.

Read it off the right column

The two definitions people mix up on a hot job site, written out in full.

Superheat = suction line temp minus sat temp at suction pressure. Read the vapour (dew) column.
Subcooling = sat temp at liquid pressure minus liquid line temp. Read the liquid (bubble) column.

Air

Airflow first. A charge chased on a system starved for air is a charge you'll be chasing again next week.

400
CFM per ton
350 to 425
16–22°F
Supply to return
at 75°F, 50% RH
−1°F
Per +10% RH
above 50%

What the split is telling you

One number you already have on the gauge, and what it means, without calling anybody.

under
14°F
Low charge, too much airflow, or a tired compressor. Check charge before you touch the blower.
16–22°F
Where it should be at 75°F and 50% RH. Slide it down about 1°F for every 10% of humidity above that.
over
24°F
Restricted air. Filter, then the coil, then the return, then the blower. In that order.

The math

Three formulas that cover most of what gets worked out in a truck.

CFM × 1.08 × ΔTSensible BTU/h
BTU/h ÷ (1.08 × ΔT)CFM
BTU/h ÷ 12,000Tons

R-454B, what is actually different

It's an A2L blend. Four handling rules and three numbers worth knowing.

A2L
ASHRAE 34
class
466
GWP
78%
Lower GWP than
R-410A

Electrical

The two checks that settle a no-cool call fastest.

Run capacitor passes at ±6%
A 40 µF cap is good anywhere from 37.6 to 42.4. Outside that, replace it. Read it with the power off and the cap discharged.
Voltage unbalance
Biggest deviation from the average, divided by the average. Per NEMA MG-1.
1%derate starts
2%run at 95%
5%run at 76%
5%+don't run it

Evacuation

The step that gets skipped, and the one that actually proves the job.

Pull below 500 microns. Then isolate the pump and watch it: holding under 1,000 microns for 10 minutes is what proves the system is dry and tight. Hitting 500 with the pump still running proves nothing.

Ranges from ACCA Manual T and manufacturer service data. A2L class per ASHRAE 34, leak detection per UL 60335-2-40, unbalance per NEMA MG-1, evacuation per ANSI/ACCA 5 QI. The nameplate and the maker's chart always win.