Oklahoma - REFRIGERATION CONTRACTOR

Key Concepts

Ohm's Law & Basic Principles - Voltage (V) = electrical pressure (EMF); measured in volts - Current (I) = electron flow; measured in amperes - Resistance (R) = opposition to flow; measured in ohms - Ohm's Law: V = I × R (rearrange as needed: I = V/R, R = V/I) - 1 ampere = 1 coulomb per second (6.24 × 10¹⁸ electrons/second)

Circuit Types - Series: Same current flows through all components; total resistance = R1 + R2 + R3; one break stops all current - Parallel: Same voltage across all branches; total resistance decreases as branches are added (1/Rt = 1/R1 + 1/R2...); one break doesn't stop other branches - Series-Parallel: Combination; solve by reducing parallel branches first, then treat as series

Power Calculations (Watt's Law) - True Power (watts): W = V × I × PF - Apparent Power (VA): VA = V × I (no power factor applied) - Power Factor (PF) = True Power (W) ÷ Apparent Power (VA); expressed as decimal (e.g., 0.85) - Single-phase power: W = V × I × PF - Three-phase power: W = V × I × 1.732 × PF (1.732 = √3)

Single-Phase vs. Three-Phase Systems - Single-phase: 120V or 240V; used for smaller equipment - Three-phase: 208V, 240V, or 480V; used for larger commercial refrigeration systems; more efficient, smoother motor operation

Key Concepts

Refrigerant Classification (ASHRAE 34) Refrigerants are classified by chemical family and safety group. Know these families cold: - CFC (Chlorofluorocarbons): R-11, R-12 — high ODP, high GWP; fully phased out - HCFC (Hydrochlorofluorocarbons): R-22, R-123 — lower ODP than CFCs; phased down under Montreal Protocol; new production banned in the U.S. as of 2020 - HFC (Hydrofluorocarbons): R-134a, R-410A, R-404A — zero ODP, high GWP; currently being phased down under AIM Act - HFO (Hydrofluoroolefins): R-1234yf, R-1234ze — zero ODP, very low GWP; newer replacements - HC (Hydrocarbons): R-290 (propane), R-600a (isobutane) — zero ODP, low GWP, but flammable - Inorganic: R-717 (ammonia), R-744 (CO₂), R-718 (water) — designated by 700-series numbers

ASHRAE 34 Safety Groups: Two-part designation — toxicity (A=lower, B=higher) and flammability (1=no flame, 2L=low flammability, 2=flammable, 3=highly flammable). Example: R-410A = A1 (low toxicity, nonflammable); R-290 = A3 (low toxicity, highly flammable).

IMC Section 1103.1: Refrigerants must be classified per ASHRAE 34 as listed in Table 1103.1. Refrigerants not in Table 1103.1 require approval before use.

Key Concepts

ACR Copper Tubing Types

• Soft-drawn (annealed) copper is used where bending is required; comes in coils; easier to work with in tight spaces.
• Hard-drawn copper is used for straight runs; comes in straight lengths; cannot be bent without annealing.
• Type L is the standard for most refrigerant piping (medium wall thickness). Type K has the heaviest wall and is used where extra strength or underground installation is required.
• ACR tubing is sold by OD (outside diameter); water/plumbing copper is sold by nominal (ID) size — do not confuse the two.
• ACR tubing is dehydrated, sealed, and charged with dry nitrogen at the factory to keep it clean and moisture-free.

Tubing Cutting and Bending

• Always use a tubing cutter for copper — produces a clean, square cut. Hacksaws leave burrs that contaminate the system; if used, deburring is mandatory.
• Ream and deburr every cut end before fitting to prevent restriction and copper shavings in the system.
• Bending springs (internal or external) prevent kinking in soft-drawn tubing for small diameters.
• Lever (mechanical) benders are used for larger diameters or harder tubing; provide consistent, accurate bends.

Refrigeration Equipment and Components (25% of Exam)

Key Concepts

Compressor Drive Configurations

• Open-drive compressors: External motor drives compressor via shaft seal; shaft seal is the critical weak point — must seal across full pressure range; used in large commercial/industrial applications
• Hermetic compressors: Motor and compressor sealed in one welded housing; no shaft seal; cannot be field-serviced internally
• Semi-hermetic compressors: Bolted housing — motor and compressor integrated but accessible for field repair; common in commercial refrigeration

Compressor Types

• Reciprocating: Piston/cylinder; uses suction and discharge valves; clearance space affects efficiency; direct-drive or belt-driven; best for small-to-medium loads with variable capacity via unloaders
• Rotary: Rotating vane or stationary blade; low-clearance volume; used in small refrigeration and A/C
• Scroll: Orbiting and fixed spiral scrolls; no suction/discharge valves; quiet, efficient; cannot run in reverse — refrigerant flows inward toward center
• Screw: Twin helical rotors (male/female); continuous compression; high efficiency at part load with slide valve unloading; common in large commercial systems
• Centrifugal: Impeller accelerates refrigerant; uses centrifugal force; suited for high-tonnage, low-pressure-ratio applications (chillers); susceptible to surge at low load

Oklahoma Refrigeration Contractor Exam | 10 Questions | 12% of Exam

Key Concepts

The Refrigeration Cycle — Four Phases - Compression: Low-pressure superheated vapor enters the compressor; exits as high-pressure, high-temperature superheated vapor. Work is added to the refrigerant here. - Condensing: High-pressure vapor rejects heat to the ambient and condenses to a liquid. Subcooling begins at the end of this phase. - Metering: High-pressure liquid passes through the metering device (TXV, fixed orifice, cap tube), dropping to low pressure and partially flashing to vapor. - Evaporation: Low-pressure refrigerant absorbs heat from the conditioned space, boiling to a vapor. Superheat develops at the end of this phase.

Pressure-Enthalpy (P-H) Diagram - The x-axis is enthalpy (Btu/lb); the y-axis is absolute pressure (psia). - The refrigeration effect is the horizontal distance across the evaporator on the diagram. - Compression work is the enthalpy difference across the compressor. - A shifted saturation curve (wider cycle) = more efficient system; a compressed cycle = system problems (low capacity, high compression ratio). - Use P-H diagrams to diagnose: low suction pressure shifts the evaporator line down; high discharge pressure shifts the condenser line up.

Key Concepts

Personal Protective Equipment (PPE) — 29 CFR 1926.20(f)

Each failure to provide PPE to an individual employee is a separate OSHA violation. The employer must provide PPE to each covered employee — not just make it available. For refrigeration work: safety glasses, chemical-resistant gloves, and face shields when handling refrigerants; hearing protection in high-noise environments.

Lockout/Tagout (LOTO)

Before servicing electrical or mechanical systems, all energy sources must be isolated and de-energized. LOTO requires: (1) notify affected employees, (2) identify all energy sources, (3) apply locks/tags to each isolation point, (4) verify zero energy state before work begins. Tags alone are not sufficient when a lockout device is feasible.

Fire Protection — 29 CFR 1926.24

The employer is responsible for developing and maintaining a fire protection and prevention program throughout all phases of construction, repair, alteration, or demolition. Portable fire extinguisher classes: - Class A – Ordinary combustibles (wood, paper) - Class B – Flammable/combustible liquids and gases - Class C – Energized electrical equipment - Class D – Combustible metals - Class K – Cooking oils (commercial kitchens)

For refrigeration worksites, a Class B:C extinguisher is typically required near flammable refrigerants and electrical panels.