Oklahoma - HVACR JOURNEYMAN UNLIMITED

Key Concepts

Ohm's Law & Watt's Law - Ohm's Law: V = I × R (Voltage = Current × Resistance) - Watt's Law: P = V × I (Power = Voltage × Current) - Combined: P = I²R and P = V²/R - 1 volt = EMF required to push 1 ampere through 1 ohm of resistance

Circuit Types - Series circuit: Same current flows through all components; total resistance = sum of all resistors (R_T = R1 + R2 + R3); voltage divides across loads - Parallel circuit: Same voltage across all branches; total resistance is less than the smallest branch resistor (1/R_T = 1/R1 + 1/R2 + 1/R3); current divides - Series-parallel: Combination of both; solve by reducing parallel sections first, then treat as series

Wiring Diagrams - Pictorial diagrams show physical component appearance and location — used for installation - Ladder diagrams show electrical control logic in horizontal rungs between two vertical power rails — used for troubleshooting - Contacts shown open = de-energized (normal) state on ladder diagrams

AC Motor Types & Starting Methods - Single-phase motors: PSC (Permanent Split Capacitor), CSIR (Capacitor Start/Induction Run), CSCR (Capacitor Start/Capacitor Run), split-phase - Three-phase motors: Self-starting; no start capacitor needed; used in larger commercial equipment - PSC motors use a run capacitor only; CSIR adds a start capacitor switched out by a relay

Key Concepts

Gas Piping Materials & Fittings

• Approved pipe types: Black steel (Schedule 40), galvanized steel, CSST (Corrugated Stainless Steel Tubing), copper (where not prohibited by gas type), and polyethylene (PE, underground only).
• CSST requires bonding per IFGC and must be installed per manufacturer listing. It is not approved for use as a connector between the piping system and an appliance.
• Polyethylene pipe is approved for underground exterior use only — never inside buildings.
• Copper tubing is prohibited with gases that contain more than 0.3 grains of hydrogen sulfide per 100 standard cubic feet (natural gas is generally acceptable; LP gas composition matters).
• Fittings must be compatible with pipe material; cast iron fittings are not permitted in gas piping systems.

Gas Piping Pressure Requirements, Testing & Leak Checking

• Test pressure: Piping systems must be tested at no less than 1½ times the maximum operating pressure, or 3 psi minimum (whichever is greater), with air, nitrogen, or CO₂ — never with gas.
• Low-pressure systems operate at ½ psi (14" W.C.) or less; medium-pressure systems operate above ½ psi up to 2 psi.
• Leak testing uses soap solution or approved detector — open flame is prohibited for leak detection.
• Test duration: typically 10 minutes minimum for systems under 3 psi; longer for larger systems.

Key Concepts

Duct System Types - Radial: Individual ducts run from central plenum to each outlet — simple, low-friction, good for small systems - Extended plenum: Large trunk duct maintains near-constant static pressure; branches tap off at intervals - Reducing trunk: Trunk decreases in size as airflow is distributed — maintains velocity and static pressure - Perimeter loop: Continuous loop duct around building perimeter; effective in slab-on-grade construction - SDHV (Small Duct High Velocity): 1.5"–3" diameter ducts, 800–1200 FPM velocity, used in retrofit applications

Duct Construction Materials - Sheet metal (galvanized steel/aluminum): Most durable; joined with S-slips, drive cleats, flanged fittings, or TDC/TDF connectors - Fiberglass duct board: R-value built in; cut and folded; joined with foil-faced tape and staples — not for high-velocity systems - Flexible duct: Wire helix with inner liner; limited to 14 ft runs per ACCA Manual D; must be fully extended — no compression or sharp bends - Sealing: All joints must be sealed with mastic or UL 181-listed metal foil tape — standard cloth duct tape is NOT acceptable per IMC

Key Concepts

Compression Refrigeration Cycle

The basic vapor-compression cycle moves heat via four processes: evaporation → compression → condensation → expansion. Refrigerant absorbs heat in the evaporator (low-pressure side), is compressed to high pressure/temperature, rejects heat in the condenser, and is metered back through the expansion device. Low-side pressure = suction side; high-side pressure = discharge side.

Compressor Types

• Reciprocating: Piston-driven; common in residential/light commercial; handles liquid slugging poorly
• Rotary (vane/rolling piston): Compact, low-vibration; common in small room ACs
• Scroll: Two interlocking spirals; highly efficient, quiet; most common in modern residential split systems; no suction/discharge valves
• Screw (helical rotary): Male/female rotors; used in large commercial/industrial; 20–200+ ton range
• Centrifugal (turbo): Dynamic compression via impeller; used in large chillers (200+ tons); sensitive to low-load surging

Metering Devices

• Capillary tube: Fixed restriction; no moving parts; system must be critically charged; used in small sealed systems
• TXV (Thermostatic Expansion Valve): Maintains constant superheat at evaporator outlet; controlled by bulb sensing suction line temperature + pressure
• AXV (Automatic/Constant Pressure Expansion Valve): Maintains constant evaporator pressure regardless of load
• EEV (Electronic Expansion Valve): Microprocessor-controlled; precise superheat management; used in inverter/variable systems
• Fixed orifice (piston): Similar to cap tube concept; must match system charge precisely

Key Concepts

Gas-Fired Heating Systems

• Combustion fundamentals: Natural gas requires approximately 10 cubic feet of air per 1 cubic foot of gas for stoichiometric combustion. Incomplete combustion produces CO; excess air reduces efficiency.
• Gas valves: Combination gas valves integrate pressure regulation, redundant safety shutoff, and flow control. Standing pilot systems use a thermocouple; intermittent ignition systems (IID) use electronic spark ignition with flame rectification proving.
• Burner types: In-shot, upshot, and inshot burners are common in forced-air furnaces. Primary air mixes before combustion; secondary air mixes at the flame.
• Ignition systems: Hot surface ignitors (silicon carbide or silicon nitride) typically operate at 120V. Flame rectification sensors pass a microamp DC signal through the flame to prove ignition — a failed sensor or grounded flame rod causes lockout.

Oil-Fired Heating Systems

• Fuel oil grades: #2 fuel oil is standard for residential/light commercial. Flash point is approximately 100°F minimum; viscosity affects atomization quality.
• Oil burners: Gun-type (pressure atomizing) burners operate at 100–140 PSI nozzle pressure. Nozzle ratings are in GPH and spray angle/pattern (solid, hollow, semi-hollow).
• Combustion efficiency testing: Use a flue gas analyzer to measure CO₂ or O₂ percentage and stack temperature. Calculate stack loss and net efficiency. Ideal CO₂ for #2 oil is 11–13%. Smoke spot testing uses a Bacharach scale of 0 (clear) to 9 (heavy smoke) — target ≤1.
• **Fuel…

Key Concepts

Lockout/Tagout (LOTO)

• Lockout (LO): Physically locking an electrical switch or disconnect in the open (off) position so the circuit cannot be re-energized during service.
• Tagout (TO): Placing a warning tag on a switch or mechanism to alert others that service is in progress — position must not be changed.
• OSHA requires lockout devices when equipment can be locked out. Tagout alone is only permitted when it provides equivalent protection to lockout.
• You must personally shut off and lock out the power source — never rely on others. Assume all circuits are live until you de-energize them yourself.
• The technician performing the work holds the key to the padlock. Tags must include your name and relevant contact information.
• LOTO applies to electrical, hydraulic, pneumatic, mechanical, and thermal systems.

Fire Hazards & Extinguisher Use (P.A.S.S.)

• P.A.S.S. method: Pull the pin, Aim at the base of the fire, Squeeze the handle, Sweep side to side.
• Fire extinguisher classes: A = ordinary combustibles (wood, paper); B = flammable liquids/gases; C = energized electrical equipment; D = combustible metals; K = cooking oils/fats.
• Use a Class C or ABC extinguisher near electrical panels and HVACR equipment.