Louisiana Heat, Air Conditioning, Ventilation, Duct Work and Refrigeration

Key Concepts

Ohm's law and Watt's law. E = I × R; R = E ÷ I; I = E ÷ R (Chapter 12, Section 12.1.3). With voltage constant, current and resistance are inversely related — lowering resistance increases current (Chapter 12, Section 12.1.3). Power: P = I × E (Chapter 13, Section 13.1). Resistance from watts and volts: R = E² ÷ P (Ohm's Law reference, Pages 1–2, 21).

Series circuits. Only one path for current, so the same current flows through every load; if any one device opens, the entire circuit is broken (Chapter 12, Section 12.4.2). Total resistance is the sum of individual resistances (Series Circuits reference, Pages 3–4). Total voltage drop equals the sum of the individual drops, which equals the total applied voltage (Chapter 12, Section 12.4.5).

Louisiana Heat, Air Conditioning, Ventilation, Duct Work and Refrigeration — 7 questions, 14% of exam

Key Concepts

Tubing sizing and identification - ACR tubing size is designated by the actual outside diameter; copper water tubing nominal size equals the OD minus 1/8″ (Modern Refrigeration and Air Conditioning, Ch. 8, Sec. 8.1.1). - ACR tubing is charged and sealed with gaseous nitrogen to keep the tubing clean and dry until used (Page 138). - Soft ACR tubing hardened by oxidation or repeated bending and hammering is work hardened; it may crack at stress points when flared and is softened by annealing (Sec. 8.1.1). - Hard-drawn ACR tubing is hard and stiff, so it needs few clamps or supports, particularly in larger diameters; it should not be bent, so flared connections cannot be used, and joints must be brazed, not soldered — solder is used only on water lines (Page 139). - Stainless steel tubing Type 304 (food processing, ice cream manufacturing, milk handling, specialized cooling coils) is connected to fittings by flaring or brazing (Page…

Key Concepts

Compression cycle dividers. The compressor and the metering device are the two dividers between the low side and the high side. The compressor draws low-pressure vapor from the evaporator and compresses it into the high side on the discharge end; the metering device separates high from low at the other end. (Pages 91–93)

Metering devices and receivers. Capillary tube systems do not use liquid receivers. Liquid receivers are usually found on larger HVACR systems with a significant charge that use low-side float or expansion valve metering devices. (Page 96) A capillary tube must be replaced with one of the same length and inside diameter; charge is critical, and overcharging or undercharging causes poor performance. (Chapter 20)

Piston-type metering orifices. High-side pressure seats the fluted piston so it meters like a normal orifice; when flow reverses, pressure lifts the piston off its seat and refrigerant flows through the flutes around the outside plus the center bore, greatly increasing flow. Heat pumps often use two: one meters in cooling and free-flows in heating, the…

Key Concepts

Clean Air Act / Section 608 - Section 608 of the Clean Air Act prohibits venting refrigerant to the atmosphere; refrigerant must be recovered and recycled, and technicians must evacuate HVACR equipment to established vacuum levels when opening it for service (Page 225). - Fines are assessed up to $37,500 per day (Page 170; the 22nd edition prints $45,000 — the penalty is adjusted for inflation yearly) for noncompliance. Violations include venting CFC, HCFC, and HFC refrigerants, failure to recover to required evacuation levels, falsifying records, working without Section 608 certification, using recovery equipment that is not EPA approved, and disposing of equipment without recovering refrigerant (Pages 170–171). - Exception: the EPA allows release of small amounts during recovery, repair, purging, and charging; purging gauge manifold hoses is not a violation (Page 216). A refrigerant-nitrogen mixture used as a trace gas for leak detection may be vented before repair (Page 1400). - Leak repair rule: repairs required within 30 days if the system contains more than 50 lb and the annual leak…

Key Concepts

Combustion and flame appearance - A proper flame has a blue inner core surrounded by light blue. A yellow flame tip indicates insufficient primary air and incomplete combustion — unburned carbon particles produce the yellow color. Orange at the outer edges is from dust particles drawn in with the primary air and is not a sign of lacking primary air. Too much primary air makes the flame noisy and causes it to jump above the burner. (Modern Refrigeration and Air Conditioning, Page 1118) - Natural gas flammability limits: lower 4.0%, upper 14.0%. Ignition temperature of natural gas is 1100°F–1200°F; LP gas 920°F–1020°F. (MRAC, Pages 1115–1118)

Flue gas analysis (MRAC, Page 1120, Figure 41-8) - Ultimate CO₂: natural gas ≈ 11.9%; LP gas ≈ 13.9%. Accounting for excess air dilution, target CO₂ is 7.6% for natural gas and 8.9% for LP gas. - O₂ should be 6–9%, ideally 7.5% for both fuels, condensing or noncondensing. - CO: ANSI maximum is 400 ppm; many manufacturers flag anything over 50 ppm. - Low CO₂ +…

Key Concepts

Appliance categories and venting type - A Category IV gas furnace is a positive-pressure venting, condensing furnace. Flue gas temperature is less than 140°F (60°C), lower than its dew point, so some flue gas condenses. These are high-efficiency furnaces with secondary heat exchangers and PVC vent piping (Modern Refrigeration and Air Conditioning, p. 1134). - A Category I furnace is a negative-pressure venting, noncondensing furnace; flue gas temperature is at least 140°F (60°C), higher than its dew point (Modern Refrigeration and Air Conditioning, p. 1134). - Design, sizing and installation of vents for Category II, III and IV appliances follow the appliance manufacturer's instructions (IFGC 501.14; also 503.6.10.3). - Low-heat appliance (residential appliance): products of combustion at the point of entrance to the flue under normal operating conditions have a temperature of 1,000°F (538°C) or less (IMC Chapter 2, Appliance Type).

Louisiana HACVDR Journeyman

Key Concepts

Pressure classification and sealing - When the designer specifies no pressure class, the 1 in. wg (250 Pa) class is the basis of compliance, except variable volume duct upstream of VAV boxes, which defaults to 2 in. wg (500 Pa) (SMACNA HVAC-DCS S1.4, p. 1.1). - Seal Class A = all transverse joints, longitudinal seams and duct wall penetrations, applying at 4 in. wg (1000 Pa) and up; Class B (transverse joints + longitudinal seams) at 3 in. wg; Class C (transverse joints only) at 2 in. wg (Table 1-1, p. 1.11). - A seam joins two longitudinally oriented edges of duct surface between two joints; helical (spiral) lock seams are exempt from sealant requirements; all other duct wall connections are joints (S1.9d). Sealing applies in both positive and negative pressure modes (S1.9f).

Key Concepts

Design conditions. The Manual J "bulls eye" for heating is 70°F dry-bulb indoors; 75°F dry-bulb is the cooling design temperature, not heating (Manual J, Section 3, Page 3-6). ASHRAE publishes three ODT values per locality: 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 (Modern Refrigeration and Air Conditioning, Page 991). HTD = indoor design temperature − outdoor design temperature (Manual J, Section 4, Page 4-2). Use the actual HTD for all heating load calculations (Manual J, Section 3, Rounding Rules).

Material values. K-value (thermal conductivity) = heat through one square foot, one inch thick, in one hour, at 1°F difference; units Btu·in/hr·ft²·°F. C-value uses the material's actual measured thickness instead (MRAC, Page 986). U-value is like C-value but adds an adjustment for boundary air films, assuming a 15 mph wind outside and a 15 fps draft inside, making U-values slightly more accurate for real-world conditions (MRAC, Pages…