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

Louisiana HVACR Licensing Exam | 7 Questions | 14% of Exam

Key Concepts

Ohm's Law & Watt's Law relate voltage (E), current (I), resistance (R), and power (P). All 12 formula variations derive from four base relationships. Memorize the wheel: any unknown can be solved with two known values.

Series Circuits have one current path. Current is the same everywhere; voltages and resistances add. Losing one component kills the entire circuit.

Parallel Circuits have multiple current paths. Voltage is the same across every branch; currents add; total resistance is always less than the smallest branch resistor. This is how HVAC loads are wired.

Single-Phase AC Motor Types: - Split-Phase (Resistance Start): Start winding has higher resistance/lower inductance. Disconnected at ~75% speed via centrifugal switch. Low starting torque; used in fans and small loads. - CSIR (Capacitor Start, Induction Run): Start capacitor + centrifugal switch. Higher starting torque than split-phase. Capacitor is in circuit only during startup. - CSCR (Capacitor Start, Capacitor Run): Uses both a start capacitor (electrolytic) and a run capacitor…

Louisiana HVAC/R Licensing Exam | 7 Questions | 14% of Exam

Key Concepts

Refrigerant Piping Materials & Installation

• ACR tubing (Air Conditioning & Refrigeration) is Type L or Type K copper, sold sealed and dehydrated. Type L is standard for refrigerant piping; Type K is used for underground or high-pressure applications.
• Refrigerant piping must be supported at regular intervals: ½" tubing every 5 ft, up to 1⅜" every 8 ft, larger sizes every 10 ft.
• No galvanized steel in refrigerant systems — refrigerant oil reacts with zinc. Use copper or steel rated for refrigerant service.
• Suction lines must be pitched toward the compressor (minimum ⅛" per 10 ft) to ensure oil return.

Tubing Joining Techniques

• Brazing (above 1000°F) is required for most refrigerant joints; soldering (below 840°F) is generally not permitted for refrigerant lines due to pressure and temperature requirements.
• Use nitrogen purge when brazing refrigerant lines to prevent copper oxide scale formation inside tubing.
• Flared connections: Use only on annealed copper; 45°…

Louisiana HVAC/R Licensing Exam — 8 Questions (16% of Exam)

Key Concepts

Compression Refrigeration Cycle

The cycle has four stages — memorize the sequence and what happens at each component: 1. Evaporator — Refrigerant absorbs heat and evaporates (low pressure, low temp). This is where cooling occurs. 2. Compressor — Raises refrigerant pressure and temperature; moves refrigerant through the system. 3. Condenser — Refrigerant releases heat to the outside and condenses to liquid (high pressure, high temp). 4. Metering Device — Drops pressure and controls refrigerant flow into the evaporator.

Heat always flows from high temperature to low temperature — the refrigerant is the medium that moves it.

Heat Transfer Principles

• Conduction — Heat transfer through direct contact (e.g., heat through a metal pipe wall).
• Convection — Heat transfer through fluid or air movement (e.g., forced-air furnace).
• Radiation — Heat transfer via electromagnetic waves without a medium (e.g., radiant baseboard heaters).
• Sensible Heat — Changes temperature, measurable with a thermometer.
• Latent Heat — Changes state (solid↔liquid↔gas)…

Key Concepts

Refrigerant Classifications (ASHRAE 34) Refrigerants are grouped by chemical composition: - CFC (chlorofluorocarbons): R-11, R-12 — highest ODP; fully phased out - HCFC (hydrochlorofluorocarbons): R-22 — moderate ODP; production ended 2020; still legal to use/recover - HFC (hydrofluorocarbons): R-410A, R-134a — zero ODP, high GWP; currently dominant - HFO (hydrofluoroolefins): R-1234yf — zero ODP, very low GWP; next-generation - HC (hydrocarbons): R-290 (propane), R-600a (isobutane) — flammable, zero ODP, low GWP - Blends: Zeotropic (R-410A, R-407C) and azeotropic (R-502) mixtures; never mix refrigerants with different ASHRAE 34 designations (IMC §1102.2.1)

Environmental Regulations - ODP (Ozone Depletion Potential): Measured relative to R-11. CFCs highest, HCFCs moderate, HFCs/HFOs = 0 - GWP (Global Warming Potential): Measured relative to CO₂ over 100 years. R-410A GWP ≈ 2,088; R-22 GWP ≈ 1,810; HFOs near zero - Montreal Protocol: International treaty phasing out ozone-depleting substances (CFCs first, then HCFCs) - Clean Air Act Section 608: EPA rule prohibiting venting of CFCs, HCFCs, and HFCs. Requires recovery before servicing, certified technicians, and proper handling

Key Concepts

Gas Piping Materials

• Steel pipe (black or galvanized) is the most common material for natural gas and LP gas inside buildings. Must comply with ASTM A53.
• Copper tubing (Types K or L) is permitted for natural gas but prohibited for LP gas in many jurisdictions — LP gas can contain contaminants that corrode copper.
• CSST (Corrugated Stainless Steel Tubing) is allowed for gas piping but must be bonded/grounded per NFPA 54 to prevent lightning-induced arc damage.
• Polyethylene (PE) pipe is permitted for underground exterior use only — never indoors or above ground.
• Fittings must be compatible with pipe material; cast-iron fittings are not permitted for gas piping.

LP Gas Properties & Storage

• LP gas (propane) is heavier than air (vapor density ~1.5) — leaks settle low and accumulate in basements and low points. Natural gas is lighter than air and rises.
• LP gas has a BTU content of approximately 2,500 BTU/ft³ vs. natural gas at ~1,000 BTU/ft³.
• Storage tanks must be located…

Key Concepts

Appliance Venting Categories (I–IV) - Category I: Non-positive vent pressure, flue gas temp high enough to avoid condensation. Vented with Type B vent (double-wall aluminum/galvanized). Most common residential gas appliances. - Category II: Non-positive pressure, condensing. Requires corrosion-resistant vent material. - Category III: Positive vent pressure, non-condensing. Requires sealed, gas-tight vent. - Category IV: Positive pressure, condensing. Requires sealed, corrosion-resistant vent (usually PVC or CPVC for high-efficiency equipment).

Vent Types - Type B: Gas appliances, Category I only. Double-wall, listed for gas. - Type BW: Wall furnaces specifically. - Type L: Oil-fired appliances and some gas appliances. Higher temperature rating than Type B. - Pellet vent: Solid-fuel pellet appliances only. Positive pressure rated.

Combustion Air (IMC Chapter 7) - Solid-fuel appliances: follow manufacturer's instructions (IMC §701.1). - Oil-fired appliances: follow NFPA 31 (IMC §701.1). - Gas-fired appliances: follow the International Fuel Gas Code (IFGC) — NOT covered in IMC Chapter 7. - Direct-vent and fireplace appliances are exempt from IMC Chapter 7 combustion air provisions. - Dampered openings: Must be interlocked with…

Key Concepts

Rectangular Duct Construction (SMACNA Standards)

• Wall gauge and reinforcement are determined by pressure classification (static pressure rating) and duct dimension. Higher pressure = heavier gauge + closer reinforcement spacing.
• Pressure classes: ½", 1", 2", 3", 4", 6", 10" w.g. — each class sets minimum sheet metal thickness and transverse joint/intermediate reinforcement requirements.
• Galvanized steel is standard; stainless or aluminum used in corrosive environments.

Round, Oval & Flexible Duct

• Round ducts are stronger per gauge than rectangular; oval duct follows round duct standards based on major/minor axis.
• Flexible duct: maximum 5-foot unsupported length; must be fully extended (no compression). Joints must be secured with mechanical fasteners + tape + mastic or UL 181B-listed closure.
• Flexible duct connections require a drawband or clamp and sealant — tape alone is not acceptable for flexible duct connections to rigid.

Key Concepts

Design Conditions (HTD / CTD) - Indoor Design Temperature (IDT): Typically 70°F heating, 75°F cooling (Manual J defaults) - Outdoor Design Temperature (ODT): Pulled from Manual J Table 1A for the specific location (e.g., New Orleans winter design ~29°F, summer ~93°F DB / 78°F WB) - Heating Temperature Difference (HTD): HTD = IDT − ODT (heating) - Cooling Temperature Difference (CTD): CTD = ODT − IDT (cooling) - Grains Difference: Difference in moisture content (grains/lb) between outdoor and indoor air — drives the latent cooling load calculation

Heat Transfer Multiplier (HTM) - HTM combines the U-value and design temperature difference into a single multiplier (Btuh/ft²) - Heat Loss HTM = U-value × HTD - Heat Gain HTM = U-value × CTD (or CLTD for opaque panels) - Applied to surface area: Q = HTM × Area