AZ HVAC cheat sheet

A.R.S. § 32-1151 requires a contractor's license issued by the Registrar of Contractors (ROC) to bid or contract for work totaling $1,000 or more in labor and materials.

License classifications pair a scope letter with a trade number: R = residential, C = commercial, L = dual; the air conditioning and refrigeration trade number is 39, so R-39, C-39, and L-39 are the HVAC licenses.

A written complaint must be filed with the ROC within two years after the act or omission that caused the alleged damage.

A.R.S. § 12-552 imposes an eight-year statute of repose on latent construction defects, running from the date of substantial completion.

Residential contractors must maintain a surety bond and pay into the Residential Contractors' Recovery Fund; bond or fund problems are grounds for license suspension.

The license number must appear on all advertising, bids, contracts, and permits issued to the contractor.

A home solicitation sale (contract signed at the buyer's residence) carries a three-business-day right of cancellation.

Unlicensed contracting is a class 1 misdemeanor on a first offense and may be elevated to a class 6 felony on a subsequent offense.

One ton of refrigeration = 12,000 Btu/h = 200 Btu/min, roughly the heat absorbed by melting one ton of ice in 24 hours.

Saturation temperature is the boiling/condensing temperature for a given pressure; superheat = actual vapor temperature minus saturation temperature at the same pressure.

Subcooling = saturation temperature at condensing pressure minus liquid-line temperature, measured at the condenser outlet.

Sensible load: Q = 1.08 × CFM × ΔT. Latent load: Q = 0.68 × CFM × Δgrains. Total load: Q = 4.5 × CFM × Δh.

The four required components of any vapor-compression circuit are compressor, condenser, metering device, and evaporator.

Metering devices: fixed orifice/piston (charge-critical, superheat varies with load), TXV (modulates to hold constant superheat), and electronic expansion valve (EEV, controlled by a stepper motor).

R-410A is a near-azeotropic 50/50 blend of R-32 and R-125 with zero ozone-depletion potential; typical pressures are about 118 psig at 40°F evaporating and 317 psig at 100°F condensing.

Latent heat of vaporization of water is about 1,070 Btu/lb at 32°F and about 970 Btu/lb at 212°F; condensate removal therefore drives a large share of the latent load.

AFUE is the seasonal efficiency of fuel-fired heating equipment: about 80% for atmospheric non-condensing furnaces and 90%+ for condensing units.

A condensing furnace adds a secondary heat exchanger that condenses flue-gas water vapor, produces acidic condensate requiring a trap and neutralizer, and vents in PVC.

Heat pump balance point is the outdoor temperature where compressor capacity equals building heat loss; below that point supplemental heat must make up the difference.

Defrost is initiated by coil temperature, time, or demand controls and is terminated by coil temperature or pressure; the auxiliary heat is energized during defrost to temper supply air.

Gas manifold pressure is typically 3.5 in. w.c. for natural gas and 10-11 in. w.c. for propane, verified with a manometer.

Nameplate temperature rise must bracket the measured supply-minus-return temperature difference; a rise above the range signals low airflow.

Nominal airflow is 400 CFM per ton; 350 CFM per ton is used where greater latent removal is wanted in humid climates.

Direct evaporative coolers lower dry-bulb temperature by adding moisture and are effective in low-humidity Arizona climates; effectiveness is typically 70-85%.

Ohm's law: V = I × R. Power: P = V × I = I² × R. Any two known values determine the third.

Branch-circuit conductors, disconnects, and controllers must be sized at not less than 125% of the motor's nameplate full-load current.

Running overload protection is separate from branch short-circuit protection and is sized from the nameplate or the manufacturer's published data.

An equipment disconnecting means must be installed within sight of the equipment and generally within 50 feet.

Low-voltage control wiring is Class 2: R to W energizes heat, R to Y energizes cooling, R to G energizes the indoor fan, and C is the common.

A PSC motor has a run capacitor in the start winding and no centrifugal switch; an ECM is a brushless DC motor that maintains programmed airflow as static pressure changes.

Start and run capacitors are rated in microfarads, usually with a tolerance of ±6% to ±10%; a bulged or leaking case means replacement.

GFCI protection is required for receptacles in garages, basements, outdoors, and within 6 feet of a sink.

Equal friction duct sizing holds pressure drop constant, commonly 0.1 in. w.c. per 100 feet of effective length, along the longest run.

External static pressure is the sum of supply and return static measured at the air handler; most residential units are rated at 0.5 in. w.c. total.

Typical velocities: supply trunk 700-900 fpm, branch ducts 400-600 fpm, return grille face 300-500 fpm.

Flex duct must be fully extended and supported; each bend should have a centerline radius of at least one duct diameter, and sag greatly increases resistance.

ACCA Manual D sizes the duct system; Manual T selects and locates registers, grilles, and diffusers.

Nominal airflow is 400 CFM per ton of cooling capacity, and room-by-room airflows should come from the Manual J room loads.

Duct joints should be sealed with mastic or listed tape; leaks in attic ducts in Arizona add both sensible and latent load to the equipment.

Return air must be ducted from each pressure-balanced zone; a single central return can starve rooms with closed doors.

Copper-to-copper joints are brazed with 5% silver-phosphorus filler (silfos) without flux; brass, steel, or dissimilar joints require flux and higher-silver filler such as 15%.

A low flow of dry nitrogen (about 2-3 CFM) is passed through the tubing during brazing to displace oxygen and prevent internal copper oxide scale.

ACR copper is cleaned, purged, and capped at the factory; refrigeration-grade tubing should be used instead of plumbing-grade copper.

Evacuation standard for a new system is 500 microns or lower, held with the pump isolated to confirm the vacuum does not rise.

Triple evacuation uses nitrogen breaks between pulls to remove moisture from the system.

Suction-line oil traps are installed at the base and top of long vertical risers, roughly every 15-20 feet of rise, to return oil to the compressor.

Suction lines are insulated with closed-cell insulation of at least 3/4-inch wall to prevent condensation and capacity loss.

Flare fittings must be made with refrigerant-rated tools and torqued to the manufacturer's specification with a torque wrench, not by feel.

ACCA Manual J calculates room-by-room loads, Manual S selects the equipment, Manual D sizes the ducts, and Manual T selects the air-distribution devices.

Total load = sensible load + latent load; equipment is selected on total capacity, and the equipment sensible heat ratio must match the calculated SHR.

SHR = sensible load ÷ total load; an oversized unit with a high SHR leaves the space humid because runtime is too short to remove moisture.

Design temperatures come from ASHRAE or Manual J tables; summer design dry-bulb values above 100°F apply across most of Arizona.

Infiltration is estimated from construction tightness, blower-door ACH50, or Manual J default values rather than guesswork.

Air density falls with altitude; at 5,000 feet the density correction factor is about 0.83, and gas heating input is derated roughly 4% per 1,000 feet above sea level.

Duct gain and loss must be added when ducts run through attics, which is standard practice in Arizona and can add significant load.

The "one ton per 500 square feet" shortcut is not a load calculation and routinely produces oversized equipment.

EPA Section 608 certification is required to purchase refrigerant and service appliances: Type I small appliances, Type II high pressure, Type III low pressure, or Universal.

A refrigerant recovery cylinder must never be filled above 80% of its water capacity; the fill is controlled by weight on a scale.

Liquid refrigerant contacting skin causes frostbite; PPE includes goggles or a face shield, gloves, and long sleeves, and refrigerant vapor displaces oxygen in enclosed spaces.

OSHA fall protection is triggered at 6 feet in construction and 4 feet in general industry, using guardrails, personal fall arrest, or nets.

Ladder setup uses the 4:1 rule (1 foot out per 4 feet of height) and the ladder must extend 3 feet above the landing surface.

Lockout/tagout requires the disconnect to be opened, locked, tagged, and the circuit verified dead with a meter before work begins.

Nitrogen cylinders require a pressure regulator; full cylinder pressure (about 2,200 psi) will rupture refrigerant tubing if applied directly.

Heat illness prevention in Arizona heat uses water, rest, shade, and gradual acclimatization, with work/rest cycles adjusted to temperature.

Gross margin % = (price − cost) ÷ price × 100; markup % = (price − cost) ÷ cost × 100. A 25% margin equals a 33.3% markup.

Break-even volume = fixed overhead ÷ gross margin ratio; labor should be priced using a burdened rate (wage × a burden factor of roughly 1.25-1.45).

An Arizona preliminary 20-day notice must be given within 20 days of first furnishing labor or materials to preserve mechanics' lien rights on a project.

Only a written, signed change order modifies contract scope, price, or schedule; unbilled extra work is generally uncollectible.

Retainage of 5-10% is commonly withheld until substantial or final completion and must be tracked in the project budget.

Cash flow depends on progress billing schedules, material deposits, and the timing of supplier and subcontractor payments.