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.
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 roof, 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.
Pull liquid from the cylinder. It's a blend, so drawing vapour changes the mix.
Cylinder threads are left hand, double ring on the knurl. System side stays right hand.
A2L rated tools and recovery tank. No ignition sources anywhere near the work.
New equipment only. Never a retrofit, never mixed with another refrigerant.
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.
Lifetime coverage, insurance backed
The system is covered. So is your labor.
One shop per territory carries the Noble lifetime warranty. On a covered failure we confirm the serial, book the work, and you get paid. The homeowner pays nothing.
Is your shop the one in your territory? It takes a phone call to find out, and only one shop per area ever gets it.