Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.
Total questions
60
Passing score
70%
Exam time
180 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Oklahoma State Portion
60 questions
Electrical Knowledge and Controls15 Q · 25%
Circuit diagrams: pictorial and ladder diagramsOhm's law and Watt's law calculationsSingle-phase and three-phase AC motors: types, starting methods, and capacitorsMotor starting relays: current, potential, solid-state, and PTC relaysPressure and temperature motor controls: cut-in, cut-out, range, and differential adjustmentMotor protection devices: fuses, circuit breakers, and bimetal/thermistor overload protectionElectrical test equipment: voltmeters, ammeters, ohmmeters, and multimetersTroubleshooting hermetic compressor motors: winding resistance, shorts, and groundsControl transformers and 24-volt control circuits
Natural Gas9 Q · 15%
Gas piping materials, fittings, and allowable pipe types (steel, copper, CSST, PE)Gas piping sizing methods and capacity tables (longest length, branch length, hybrid pressure)Gas piping pressure requirements, testing, and leak checksCombustion air requirements for gas-fired appliances (indoor, outdoor, and combination methods)Venting system types and selection by appliance category (Type B, single-wall, direct-vent, Categories I-IV)Chimney and vent sizing for Category I appliances (draft hood and fan-assisted)Vent connector installation requirements, clearances, and termination locationsGas furnace combustion principles, ignition systems, and safety controls
Air Distribution Systems10 Q · 17%
Duct types, construction materials, and system configurations (radial, extended plenum, reducing trunk, perimeter loop, SDHV)Duct sizing procedures and ACCA Manual D requirementsRegisters, diffusers, and grilles — selection, placement, and airflow characteristicsDampers — types (butterfly, multiple-blade, split, fire, smoke), installation, and automatic controlsDuct insulation, sealing methods, and vapor retarder requirements (IMC Chapter 6)Airflow measurement tools and techniques (flow hoods, manometers, pitot tubes, blower door testing, duct blaster testing)Ventilation requirements — air changes per hour, fresh air intake, positive/negative pressure, and IMC Chapter 4 outdoor airflow ratesDuct system service — balancing, noise troubleshooting, cleaning procedures, and air filter maintenance
Refrigeration and Air Conditioning Systems13 Q · 22%
Compression refrigeration cycle components and operationRefrigerant classification, properties, and environmental regulations (EPA/Clean Air Act)Refrigerant handling equipment: cylinders, gauge manifolds, service valves, and leak detectionRefrigerant recovery, recycling, reclaiming, evacuation, and charging proceduresMetering devices: capillary tubes, TXVs, AXVs, EEVs, and fixed-orifice typesCompressor types, configurations, and safety protection componentsHeat exchangers: evaporator and condenser types, defrost methods, and head pressure controlRefrigerant flow components: filter-driers, sight glasses, check valves, solenoid valves, and pressure-regulating valves
Heating Systems10 Q · 17%
Gas-fired heating systems: burners, ignition systems, and combustion controlsOil-fired heating systems: burner components, fuel delivery, and combustion efficiency testingHydronic heating system components: boilers, circulating pumps, expansion tanks, and terminal unitsHeat pump operation: reversing valves, metering devices, and heating/cooling modesElectric resistance heating systems: furnaces, duct heaters, baseboard units, and radiant heatHydronic system designs: series loop, one-pipe, two-pipe, zoned, and radiant systemsBoiler safety controls and code requirements: pressure relief valves, low-water cutoffs, and IMC Chapter 10 provisionsForced-air furnace types and efficiency ratings: upflow, downflow, condensing vs. noncondensing, and AFUE
Safety3 Q · 5%
Electrical hazards and lockout/tagout (LOTO) proceduresFire hazards and fire extinguisher use (P.A.S.S.)Refrigerant cylinder safety and pressure hazardsPersonal protective equipment (PPE) selection and useHazard Communication Standard (HCS), GHS labeling, and safety data sheets (SDS)Breathing hazards and respiratory protectionLadder, scaffolding, and fall protection safetyConfined space safety and safe work practices
Key Distinctions
Pictorial Wiring DiagramvsLadder Diagram
Pictorial diagrams show the approximate physical location of devices and may include wire colors, while ladder diagrams show the order of component operation using horizontal rungs between two vertical power lines.
Chapter 16, Section 16.3.5 — Positive Temperature Coefficient Relays
PTC Relay (cool state)vsPTC Relay (heated state)
When cool, a PTC thermistor has low resistance (3–12 Ω) directing current through itself rather than the run capacitor; once heated to its set point, resistance rises dramatically (10–20 kΩ), forcing current through the run capacitor instead.
Chapter 16, Section 16.3.5 — Positive Temperature Coefficient Relays
Solid-State Relay (SSR)vsElectromagnetic Relay
SSRs use electronic components (transistors, SCRs, or triacs) with no moving mechanical parts to switch circuits, whereas electromagnetic relays use mechanical contacts that physically move to open or close a circuit.
Chapter 16, Section 16.3.5 — Solid-State Relays
Potential RelayvsCurrent Relay
A potential relay actuates based on the counter-EMF (voltage) generated in the start winding as the motor approaches rated speed, while a current relay actuates based on the change in run-winding current draw as the motor accelerates.
Chapter 16, Section 16.3.5 — Potential Relays
Building-Related Illness (BRI)vsSick Building Syndrome (SBS)
BRI is a specifically diagnosable illness caused by airborne agents whose symptoms persist even after the occupant leaves the building, whereas SBS has no specific identifiable cause and symptoms disappear when occupants leave.
Modern Refrigeration and Air Conditioning, Page 730
K-value measures heat flow through a standardized one-inch-thick sample of material per square foot per hour per 1°F difference, while C-value describes thermal conductance based on the material's actual measured thickness.
Modern Refrigeration and Air Conditioning, Page 986
In-Line AmmetervsClamp-On Ammeter
An in-line ammeter is connected in series with the load and requires correct DC polarity (black negative, red positive), while a clamp-on ammeter clamps around a single wire and measures current via magnetic field induction without breaking the circuit.
Chapter 17, Section 17.1.3 — In-Line Ammeters
Range Adjustment (Low-Pressure Motor Control)vsDifferential Adjustment (Low-Pressure Motor Control)
Turning the range screw clockwise raises both cut-in and cut-out pressures equally without changing the differential, while turning the differential screw clockwise raises only the cut-out pressure, narrowing the operating band.
Chapter 16, Section 16.3.4 — Low-Pressure Motor Controls
Series CircuitvsParallel Circuit
In a series circuit there is a single current path so opening any one device (switch, fuse, or load) breaks the entire circuit, whereas in a parallel circuit each load has its own path and other loads continue operating if one path opens.
Chapter 12, Section 12.4.2
Hot-Surface Ignition (HSI) System — Glow CoilvsHot-Surface Ignition (HSI) System — Flame Rod
The glow coil is used solely for ignition and cannot sense flame, while the flame rod performs flame sensing via flame rectification and signals the control module to keep the gas valve open.
Modern Refrigeration and Air Conditioning, Pages 1126-1128 (Sections 41.5.4 and 41.6.1)
Multipurpose FusevsCurrent-Limiting Fuse
A multipurpose fuse combines time-delay and fast-acting characteristics—tolerating brief high starting currents but opening immediately above 500% overload—while a current-limiting fuse uses a temperature-sensitive resistor that opens on overcurrent and then resets (closes) after cooling.
Chapter 16, Section 16.4.1
Duct Leakage Test (before air handler installed)vsDuct Leakage Test (with air handler installed)
When tested before the air handler is installed, maximum permitted leakage is 3 cfm per 100 ft² of conditioned space; when tested with the air handler installed, the maximum rises to 4 cfm per 100 ft².
Modern Refrigeration and Air Conditioning, Page 793
Key Terms
cfm50 Modern Refrigeration and Air Conditioning, Page 791
The measured airflow through a blower door fan when indoor pressure is held at −50 Pa with respect to outdoors, used to calculate ACH50 (air changes per hour at that pressure difference).
cfm25 (Duct Leakage Test) Modern Refrigeration and Air Conditioning, Page 792
The airflow required to maintain ductwork at +25 Pa with respect to the conditioned space during a duct leakage test, per IECC standards.
Velocity Pressure Modern Refrigeration and Air Conditioning, Page 710
The difference between total air pressure and static air pressure as measured by a pitot tube; total pressure equals static pressure plus velocity pressure.
The voltage induced in a motor's start winding as the motor approaches rated speed; used by a potential relay to determine when to drop the start capacitor out of the circuit.
Flame Rectification Modern Refrigeration and Air Conditioning, Pages 1126-1128 (Sections 41.5.4 and 41.6.1)
The electronic process by which a flame rod senses a burner flame and sends a microamp signal back to the ignition control module to confirm the flame is present and keep the gas valve open.
Draft (Combustion) Modern Refrigeration and Air Conditioning, Page 1155
The movement of flue gas through a heat exchanger, measured in inches of water column (in. WC) by a draft gauge; draft indicates how quickly combustion gases pass through and how much heat is transferred versus escaping through the flue.
Thermal Conductivity (K-Value) Modern Refrigeration and Air Conditioning, Page 986
A measure of how much heat passes through one square foot of material one inch thick in one hour with a 1°F temperature difference between the two sides, expressed in Btu·in/hr·ft²·°F.
A respirator that provides supplemental oxygen and must be used when ambient oxygen levels fall below 19.5% or when contaminants cannot be adequately filtered.
Perimeter Loop Duct System Modern Refrigeration and Air Conditioning, Page 755
A duct system used with downflow furnaces in homes without basements where ductwork is embedded in a concrete slab with branch ducts connecting to a perimeter loop duct and floor diffusers.
Radial Duct System Modern Refrigeration and Air Conditioning, Page 755
A duct system in which individual branch ducts run directly from the central plenum to each supply outlet with no trunk line.
Small Duct, High-Velocity (SDHV) System Modern Refrigeration and Air Conditioning, Page 748
An air distribution system using small-diameter ducts delivering air at high velocity to the building perimeter, with return air originating from the center of the building.
High-Pressure Motor Control Cut-Out Setting Chapter 16, Section 16.3.4 — High-Pressure Motor Controls
A safety control set to cut out the compressor at 20% above normal head pressure to protect the compressor and motor from high pressure and temperature.
A device located inside the compressor on or in the motor windings that opens the circuit when excessive current or heat bends the bimetal disc, then resets automatically when the motor cools.
Panned Joist Space Modern Refrigeration and Air Conditioning, Page 755
A common return-air branch duct construction method in basements where the floor joists and floorboards form three sides of the duct.
Distributor (Refrigerant) Modern Refrigeration and Air Conditioning, Pages 490-491
A device connected to the outlet of a metering device on a large evaporator that splits refrigerant flow into multiple parallel circuits to reduce pressure drop and provide more consistent evaporator temperature.
Formulas to Know
Ohm's Law — ResistanceR = E ÷ I (Resistance [Ω] = Voltage [V] ÷ Current [A])
Ohm's Law — CurrentI = E ÷ R (Current [A] = Voltage [V] ÷ Resistance [Ω])
Ohm's Law — VoltageE = I × R (Voltage [V] = Current [A] × Resistance [Ω])
Watt's Law — Power (single-phase)P = I × E (Power [W] = Current [A] × Voltage [V])
Series Circuit — Total Voltage DropVD_total = VD1 + VD2 + VD3 + … = V_applied
Series Circuit — Current (same through all loads)I = V_total ÷ R_total (single current value flows through every series load)
Control DifferentialDifferential = Cut-Out Value − Cut-In Value
Total Air PressureTotal Pressure = Static Pressure + Velocity Pressure
