HVAC Excellence Master HP cheat sheet

Sensible heat equation: Q = 1.08 × CFM × ΔT (BTU/h, standard air); latent form Q = 0.68 × CFM × Δgrains, and total Q = 4.5 × CFM × Δh.

Standard air density is 0.075 lb/ft³ at 70 °F sea level; at 5,000 ft use roughly 0.062 lb/ft³ and derate airflow-based capacity about 17 percent.

Superheat = actual suction line temp − saturated suction temp at the same pressure; target 8–12 °F at the evaporator outlet for a fixed-orifice system.

Subcooling = saturated condensing temp − liquid line temp; target 8–12 °F on TXV systems, measured at the condenser outlet.

Pressure–temperature relationship is refrigerant-specific: R-410A at 118 psig ≈ 40 °F; R-32 at 101 psig ≈ 40 °F; R-134a at 35 psig ≈ 40 °F.

1 psi = 2.31 ft of water column head; 1 ton of refrigeration = 12,000 BTU/h = 200 BTU/min.

Airflow check: CFM ≈ 400 per nominal ton; a 3-ton system should move roughly 1,200 CFM, verified by temperature rise or static pressure.

Recovery vs recycling: recovery removes refrigerant to a container; recycling cleans it for reuse in the same equipment; reclaim restores to ARI 700 purity.

SEER2 uses the same M1 blower static (0.5 in. w.c.) but higher external static; HSPF2 uses a 5 °F colder outdoor bin, so HSPF2 values run about 15 percent below HSPF.

Duct leakage in the 2021 IECC is limited to 4 CFM per 100 ft² of conditioned floor area at 25 Pa for new homes; older homes commonly test 15–30 percent.

A 10 percent refrigerant undercharge can reduce capacity roughly 5–10 percent and raise compressor discharge temperature; check superheat before adding charge.

Condenser subcooling falls and suction superheat rises when the system is undercharged; the opposite pattern suggests overcharge or a restricted liquid line.

Airflow below 350 CFM/ton lowers sensible capacity and can freeze the coil; airflow above 450 CFM/ton reduces latent removal and raises blower watts.

Energy factor benchmarks: a properly tuned 3-ton split system should hold 18–22 °F temperature split across the coil at 400 CFM/ton and 80 °F return.

Compressor isentropic efficiency typically 65–75 percent; a worn compressor shows higher current draw per ton and lower head pressure than the performance curve predicts.

Economizer high-limit setpoints in ASHRAE 90.1 are 65–75 °F for differential dry-bulb control; verify changeover with a calibrated reference thermometer.

Section 608 certification is required to buy or handle ozone-depleting refrigerants; EPA 608 Type I covers small appliances, Type II high-pressure, Type III low-pressure, Type IV all.

R-410A is an A1 refrigerant (no flame propagation, low toxicity); R-32 is A2L (lower flammability) and requires ignition-source controls and leak detection per ASHRAE 15.

A2L charge limits: for a residential system, the maximum charge is based on the lower flammability limit and room volume; typical limits for R-32 are around 26 lb in a 300 ft³ room per ASHRAE 15.

Venting refrigerant to the atmosphere is prohibited; recovered refrigerant must be recycled, reclaimed, or destroyed, and cylinders must be DOT-approved and never overfilled beyond 80 percent.

Leak repair requirements: for appliances with 5 or more lb charge, leaks must be repaired within 30 days of discovery; for comfort cooling with 50+ lb charge, EPA requires repair within 30 days and verification within 10 days.

R-22 phase-out: production and import ended January 1, 2020; reclaimed R-22 remains legal for servicing existing equipment but is not permitted in new equipment.

GWP values: R-410A ≈ 2,088; R-32 ≈ 675; R-454B ≈ 466; R-134a ≈ 1,430; R-1234yf < 1. The AIM Act targets an 85 percent HFC reduction by 2036.

Personal protective equipment for A2L and high-pressure work includes safety glasses, gloves rated for the refrigerant, and a calibrated leak detector; never use open flame to detect leaks.

Ohm's law: V = I × R; power P = V × I × PF. A 240 V single-phase compressor drawing 12 A at 0.9 PF consumes about 2,592 W.

Locked rotor amps (LRA) is typically 5–6 times running load amps (RLA); a compressor tripping on overload with LRA current indicates a seized or shorted winding.

Capacitor check: measure microfarads with a meter rated for the value; a run capacitor more than 10 percent below nameplate should be replaced.

Start relay and potential relay: measure resistance across the start winding; a reading of infinity or zero indicates an open or shorted winding.

Thermostat wiring: R to W calls heat, R to Y calls cool, R to G calls fan; a blown low-voltage fuse often follows a shorted contactor coil or miswired thermostat.

Superheat and subcooling are the primary diagnostic readings; static pressure across the coil confirms airflow, and amp draw confirms mechanical load.

Sequence of operation for a gas furnace: call for heat → inducer proves via pressure switch → igniter energizes → gas valve opens → flame sensor proves → blower delays on.

Use a clamp meter and a true-RMS multimeter; verify 24 V control voltage at the transformer secondary before condemning a control board.