Oklahoma HVACR Journeyman Unlimited

15 questions · 21% of the exam

Key Concepts

Circuit diagrams - A pictorial diagram shows all connections among a circuit's devices and the approximate physical location of devices in a unit; it may also give the colors of wires running to and from devices (Ch. 16, Sec. 16.1.1). - A ladder diagram has two vertical lines that are the power supply and horizontal lines (rungs) containing the various controls and loads. Each rung is an individual circuit that has a load and may also contain switches, relays, or control devices. Each line is usually numbered to keep everything organized (Ch. 16, Sec. 16.1.2). - Ladder diagrams reflect the order of component operation: devices near the top are energized and started before devices further down (Ch. 16, Sec. 16.1.2).

Ohm's law, Watt's law, circuits - E = I × R; R = E ÷ I; I = E ÷ R (Ch. 12, Sec. 12.1.3). With voltage constant, current and resistance are inversely related — lowering resistance increases current. - A watt is the power produced when one ampere flows due to a potential difference of one volt (Ch. 13, p. 273 (22nd ed.; 292 in the 20th)). P = I × E (Ch. 13, Sec. 13.1). - Series circuit: single path; the same current flows through all loads, and if any device opens the whole circuit stops conducting (Ch. 12, Sec. 12.4.2).…

Key Concepts

Scope & materials - The IFGC covers natural gas piping with an operating pressure of 125 psig or less (IFGC 2024, 101.2.3; 2018 ed. 101.2.2). - Cast-iron pipe shall not be used (403.3.1; 2018 ed. 403.4.1). Wrought-iron, stainless steel and aluminum-alloy are permitted under conditions. - Brazing alloys for nonferrous pipe/tubing shall not contain more than 0.05-percent phosphorus (403.9.1). - Plastic pipe: outdoors underground only, not over 100 psig for natural gas or 30 psig for LP-gas (404.17.1).

Installation - Burial depth 12 inches minimum (404.12); 8 inches for individual lines to outdoor lights, grills and appliances where approved and not subject to damage (404.12.1). - Conduit beneath a building with one end outdoors extends not less than 4 inches outside the building, vented above grade (404.14.1). Conduit with both ends indoors extends 2 inches beyond where the pipe emerges from the floor (404.8.2). - Shield plates: steel, not less than 0.0575 inch (No. 16 gage), where piping is less than 1½ inches from the framing face (404.7.3). - Support spacing, Table 415.1: ½ in. = 6 ft; ¾ in. or 1 in. = 8 ft; 1¼ in. or larger horizontal = 10 ft.

Key Concepts

Duct system types - Perimeter loop system — used with downflow furnaces in homes without basements; ductwork laid in the concrete slab, branch ducts connect to a perimeter duct, diffusers at intervals along the floor (MRAC p. 672 (22nd ed.; 755 in the 20th)). - Radial duct system — individual branch ducts run directly from the central plenum to each supply outlet, no trunk line (MRAC p. 672 (22nd ed.; 755 in the 20th), Figure 29-11). - SDHV (small duct, high-velocity) — small-diameter (typically 2-inch round) flexible ducts delivering air at high velocity to compact outlets; supply air to the inside perimeter, return air from the center of the building (MRAC p. 666 (22nd ed.; 748 in the 20th), Figure 29-3).

Duct construction & code (IMC 2024, Chapter 6) - Crimp joints for round/oval metal ducts: lapped not less than 1 inch, male end extending into the adjoining duct in the direction of airflow — §603.4.2. - Nonmetallic ducts: Class 0 or Class 1 material, comply with UL 181; air temperature shall not exceed 250°F (121°C) — §603.5. - Gypsum board ducts: return air only, air temperature not exceeding 125°F (52°C), surface temperature above airstream dew point, not with evaporative cooling — §603.5.1. - Flexible air ducts are not limited in length (§603.6.1.1); flexible air connectors are limited to 14 feet (§603.6.2.1). - Duct classification: positive or negative **0.5, 1.0,…

Key Concepts

Cycle and pressure divisions - The compressor and the metering device are the two dividers between the low side and the high side; the compressor divides them at the discharge end (MRAC pp. 126–128 (22nd ed.; 91–93 in the 20th)). - Refrigerant quality of 10% means 10% vapor, 90% liquid (p. 1273 (22nd ed.; 1372 in the 20th)).

Metering devices - Capillary tube systems do not use liquid receivers; receivers are found on larger systems using low-side float or expansion valve metering (p. 96). - With a static (fanless) condenser, the capillary tube must be about 10% longer than with a fan-cooled condenser (Ch. 20, p. 144 (22nd ed.; 473 in the 20th)). When a cap tube is replaced, also install a new liquid line filter-drier (Ch. 20, p. 146 (22nd ed.; 475 in the 20th)). - All systems should have a liquid line filter-drier installed (Sec. 6.4.4, p. 123) — required after TXV or component replacement. - A piston-type metering orifice lifts off its seat on flow reversal; refrigerant flows through the flutes around the outside of the piston plus the center bore (p. 146 (22nd ed.; 476 in the 20th)). - A distributor splits flow into parallel circuits, reducing evaporator pressure drop and evening out coil temperature (pp. 1088–1089 (22nd ed.; 490–491 in the 20th)). - Charge checking: subcooling for TXV systems (p. 221 (22nd ed.; 236 in…

Oklahoma HVACR Journeyman Unlimited

Key Concepts

Electric heating - 1 kW of electric resistance heat = 3,413 Btu/hr (Modern Refrigeration and Air Conditioning, p. 832 (22nd ed.; 1194 in the 20th)). - A sequencer closes and opens contacts on a time delay, energizing heating elements in sequence (typically about 30 seconds apart) to minimize initial current draw and prevent disturbances such as flickering lights (pp. 834 (22nd ed.; 1196 in the 20th), 1205). A sequencer whose contacts fail to close leaves its element de-energized, causing low heat output (pp. 841–844 (22nd ed.; 1205–1206 in the 20th)). - Line-voltage thermostats are used primarily for electric baseboard resistance heaters, wire directly to the heater with no step-down transformer, and typically operate at 120 Vac or 240 Vac (p. 952). A double-pole switch opens both legs of a 240 V circuit and is safer than a single-pole (p. 846 (22nd ed.; 1210 in the 20th)). - Electric duct furnaces shall comply with UL 1996 (IMC 2024, Section 911.1).

Oklahoma HVACR Journeyman Unlimited · 3 questions (4% of exam)

Key Concepts

OSHA and safety certifications - The national law covering workplace safety is the Occupational Safety and Health Act (OSHA). It covers both equipment safety requirements and the personal safety of the technician (Section 2.1 Safety and the Government). - Companies must report to OSHA every fatality or permanently disabling injury, or any accident involving three or more hospitalized injuries (Section 2.1). - The OSHA 10-hour class is intended for entry-level workers; the 30-hour class is designed for workers with some safety responsibility (Section 2.4.8 Safety Certifications). - The four most common hazards in the trades: falls, electrical accidents, "caught-between" accidents, and "struck-by" accidents (Chapter 2 Introduction).

Fire hazards and extinguishers - Fire classes by material consumed: Class A — ordinary combustibles (wood, paper, textiles), requires cooling-quenching; Class B — flammable liquids (grease, gasoline, oils, paints), requires blanketing/smothering; Class C — electrical equipment (motors, switches), requires a nonconducting agent; Class D — combustible metals (magnesium, lithium), requires blanketing/smothering (Section 2.2.2 Fire Hazards, Figure 2-5). - Never use water on an electrical (Class C) fire due to the high risk of electrical shock — use only a Class C–rated extinguisher (Section 2.2.2, Safety Note).

• The average fire extinguisher contains only ten seconds of extinguishing power (Section 2.2.2).