New Jersey Master HVACR Contractor Exam

Key Concepts

Ohm's Law and the power wheel. Ohm's Law relates voltage (E, volts), current (I, amperes), and resistance (R, ohms): E = I × R, I = E ÷ R, R = E ÷ I. Power in watts is added through the chart formulas P = E × I, P = E² ÷ R, and P = I² × R (Ugly's Electrical References, 2023 ed., Ohm's Law, Page 1). Modern Refrigeration and Air Conditioning (22nd ed.) calls P = I × E Watt's law (Section 14.1.1, Page 273) and states Ohm's law resistance as R = E ÷ I (Section 13.1.3, Page 256).

Series circuits — three rules (Ugly's, Series Circuits, Page 3): - Rule 1: Total current equals the current in any other part of the circuit — I_T = I₁ = I₂ = I₃. - Rule 2: Total voltage equals the sum of the voltage drops — E_T = E₁ + E₂ + E₃. - Rule 3: Total resistance equals the sum of the resistances — R_T = R₁ + R₂…

Key Concepts

Tubing identification and materials (Modern Refrigeration and Air Conditioning, 22nd ed., Ch. 5) - ACR tubing size is designated by the actual outside diameter; copper water tubing nominal size = OD minus 1/8″ (p. 71, Sec. 5.1.1). - Copper tubing comes in Type K (heavy wall) and Type L (medium wall); Type L is the commonly used type (Sec. 5.1.1). - Steel pipe is not generally used to circulate refrigerant; the major exception is ammonia refrigeration systems, because ammonia may chemically react with copper tubing (p. 74, Sec. 5.2.3). - Plastic pipe maximum service temperatures: ABS 180°F (82°C) (span –40°F to 180°F), PVC safe range –100°F to 175°F, CPVC 210°F (99°C); CPVC is rated for 100 psi (700 kPa) water pressure at 180°F (82°C) (p. 73, Sec. 5.2.2).

Key Concepts

Compression cycle dividers. The compressor divides the low side from the high side on the discharge end; the metering device is the other divider at the opposite end of the cycle (Ch. 8, p. 128).

Liquid line. All systems should have a liquid line filter-drier installed to keep moisture, dirt, and metal out of the metering device — install a new one whenever the system is opened to replace a component such as a TXV or capillary tube (Section 8.3.3, p. 130; Ch. 20). Some flash gas is acceptable, but excessive flash gas in the liquid line reduces evaporator efficiency and can damage an expansion valve (Section 8.3.2, p. 130).

Compressors. Scroll: vapor pockets shrink toward the center and discharge through the center port (Section 9.1.2, p. 141). Scroll capacity is modulated by a bypass port partway between the outer edge and the center of the fixed scroll, a variable-speed motor, or briefly separating the scrolls — not by cylinder unloaders (Section 9.1.2, p. 141). Reciprocating compressors with cylinder unloaders usually unload…

Refrigerants and Refrigeration (8 questions, 16%)

Key Concepts

Cylinders and cylinder safety - Recovery cylinders are identified by gray paint on the lower portion and yellow paint on the upper portion (Ch. 11, p. 189, Section 11.1.3). - A refillable refrigerant cylinder should be filled no more than 80% — liquid expands as temperature rises and can rupture an overfilled cylinder (Ch. 2, p. 21, "Refrigerant Cylinder Safety"). - DOT: cylinders that have contained a corrosive refrigerant must be inspected and recertified every five years; cylinders containing noncorrosive refrigerants every ten years (Ch. 11, p. 188). - Tare weight = the weight of the cylinder when empty, stamped on the cylinder; the digital scale subtracts it from total weight (Ch. 11, p. 215).

Key Concepts

Combustion chemistry and air requirements - Natural gas requires 10 ft³ of air per 1 ft³ of gas for complete combustion; about 15 ft³ of air per cubic foot of gas is supplied to give 50% excess air (Modern Refrigeration and Air Conditioning 22nd ed., Ch. 33, p. 758). - LP gas requires 24 ft³ of air to burn 1 ft³ of gas; about 35 ft³ provides 50% excess air (p. 758–761 text). - Lower-efficiency furnaces take in 20%–50% excess air; higher-efficiency furnaces use as little as 10% (p. 758).

Combustion analysis targets - Ultimate CO₂ is approximately 11.9% for natural gas and 13.9% for LP gas, but after excess-air dilution the flue-gas CO₂ should be closer to 7.6% (natural gas) and 8.9% (LP gas) (p. 759). - Flue-gas O₂ should be 6%–9%, ideally 7.5%, for both fuels, condensing or noncondensing (p. 759). - ANSI maximum CO in furnace flue gas is 400 ppm; many manufacturers treat more than 50 ppm as a problem (p. 759). - Low CO₂ + high O₂…

New Jersey Master HVACR Contractor Exam — 5 questions (10%)

Key Concepts

Combustion air (IFGC Chapter 3) - Where all combustion air is provided by a mechanical air supply system, air shall be supplied from the outdoors at a rate not less than 0.35 cfm per 1,000 Btu/h of total input rating of all appliances in the space (IFGC 304.9, Page 3-6). - Each appliance served shall be interlocked with the mechanical air supply system to prevent main burner operation when the air supply system is not operating (IFGC 304.9.2). - Indoor combustion air, standard method: minimum required volume is 50 cubic feet per 1,000 Btu/h of appliance input rating (IFGC 304.5.1). - Combustion air intake openings on the building exterior shall have their lowest side not less than 12 inches vertically above adjoining finished ground level (IFGC 304.11, Item 8). - Louvers/grilles of unknown design: assume wood louvers 25-percent free area, metal louvers and grilles 75-percent free area; screens not smaller than 1/4-inch mesh (IFGC 304.10). - IMC 701.2: **Manual dampers shall not…

Key Concepts

Airflow and leakage testing - An air handler flowmeter is placed in the air stream of an air handler to measure the total airflow of a central system; these are typically sized to fit over a large return grille or in the space normally occupied by the system's air filter (Modern Refrigeration and Air Conditioning, 22nd ed., Ch. 31, p. 701). - Duct leakage test: after all registers and grilles are sealed, the ducts are pressurized to +25 Pa WRT the conditioned space; the airflow needed to maintain that pressure is cfm25 (Ch. 31, p. 703). - Per the IECC, maximum duct leakage is 4 cfm per 100 ft² of conditioned space when ducts are pressurized to 25 Pa, and 3 cfm per 100 ft² if the ductwork is tested before the air handler is installed (Ch. 31, Section 31.1.5, p. 703). - Duct testing is not required when the air handler and ductwork are contained within the building envelope (Code Alert, p. 703). - cfm50 is the measured airflow through a…

NJ Master HVACR Contractor Exam — 5 questions (10%)

Key Concepts

Design conditions - Manual J indoor design "bulls eye": 70°F db for heating (Section 3, Page 3-6) and 75°F db at 50% RH for cooling (Sections 3-6, 3-7). - HTD = indoor heating db − 99% outdoor value; CTD = 1% outdoor value − indoor cooling db (Section 6-3, Worksheet A). - Heating outdoor db values are the ASHRAE 99 percent values — outdoor temp is colder than design about 1% of cold-month hours, roughly 85 to 90 hours per year (Section 18-1). - Textbook ASHRAE ODT selection: 99.6% for residences and small, poorly insulated office buildings; 99% for well-constructed, well-insulated buildings with a standard number of windows; 97.5% for large buildings with considerable thermal capacity and small total window area (Ch. 32, p. 722). IDT generally 70°F or 72°F; unheated spaces are assumed halfway between IDT and ODT.