Exam Cheat Sheet · Quick Reference
Oklahoma HVACR Contractor, Limited
Oklahoma · PSI Services Contractor
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
80
Passing score
70%
Exam time
210 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Oklahoma State Portion 80 questions
Electrical Knowledge and Controls
15 Q · 19%
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 Gas
12 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 Systems
15 Q · 19%
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 Systems
20 Q · 25%
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 Systems
15 Q · 19%
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
Safety
3 Q · 4%
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
A pictorial diagram shows all connections plus the approximate physical location of devices in the unit (and often wire colors), while a ladder diagram shows the order of component operation as horizontal rungs between two vertical power lines, with devices near the top energized first.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 18 - Electrical Troubleshooting Fundamentals, Page 369 (Section 18.2.2) (20th ed.: Chapter 16, Section 16.1.1)Motor startervsContactor
A motor starter is like a contactor but adds built-in overload protection to prevent motors from burning out or overheating; both use electromagnetic coils and both can be rebuilt.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 341 ("Contactors and Motor Starters") (20th ed.: Chapter 16, Section 16.3.5 — Contactors and Motor Starters)Weight-operated current relayvsRotary-solenoid current relay
A weight-operated current relay must be mounted level, whereas a current relay using a rotary solenoid can be mounted in any position.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 338 ("Current Relays") (20th ed.: Chapter 16, Section 16.3.5 — Current Relays)Solid-state relay (SSR)vsElectromagnetic relay
An SSR switches circuits with electronic components (transistors, SCRs, triacs) and has no physical movement of mechanical parts, unlike a mechanically switched electromagnetic relay; SSRs are typically used to start single-phase motors.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 345 ("Solid-State Relays") (20th ed.: Chapter 16, Section 16.3.5 — Solid-State Relays)Hard lockoutvsSoft lockout
A hard lockout shuts the furnace down for an unspecified time after a failed trial for ignition and requires a service call or power interruption to reset, while a soft lockout automatically retries after a waiting period.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 33 - Gas-Fired Heating Systems, Page 770 (20th ed.: Page 1129)Building-related illness (BRI)vsSick building syndrome (SBS)
BRI is a specifically diagnosable illness caused by airborne agents whose symptoms do not disappear when the occupant leaves the building, while SBS has no specific cause or identifiable illness and its symptoms disappear once occupants leave.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 29 - Air Quality, Page 647 (20th ed.: Page 730)K-value (thermal conductivity)vsC-value (thermal conductance)
K-value is based on a standardized one-inch thickness (Btu·in/hr·ft²·°F), while C-value is based on the material's actual measured thickness.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 32 - Heating and Cooling Loads, Page 717 (20th ed.: Page 986)ACR tubing sizingvsCopper water tubing sizing
ACR tubing is designated by its actual outside diameter, while copper water tubing nominal size equals the outside diameter minus 1/8″.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 5 - Working with Tubing and Piping, Page 71 (Section 5.1.1) (20th ed.: Chapter 8, Section 8.1.1)Subcooling charging methodvsSuperheat charging method
The subcooling method is used to check charge on systems with thermostatic expansion valves, while the superheat method is used on systems with fixed-orifice metering devices such as capillary tubes.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 12 - Working with Refrigerants, Page 221 (20th ed.: Page 236)Fusible link high-temperature cutoffvsBimetal disc high-temperature cutoff
A fusible link cannot be reset once it opens and must be replaced entirely (after investigating the cause of overheating), whereas a bimetal disc can be reset.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 35 - Electric Heating Systems, Page 845 (Section 35.5) (20th ed.: Pages 1208-1209)Range adjustment (low-pressure motor control)vsDifferential adjustment (low-pressure motor control)
Turning the range screw clockwise raises both cut-in and cut-out an equal amount without changing the differential, while the differential screw turned clockwise raises only the cut-out pressure and leaves the cut-in unchanged.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 333 (Section 17.4.4) (20th ed.: Chapter 16, Section 16.3.4 — Low-Pressure Motor Controls)Liquid line connection for recoveryvsDischarge service valve connection for recovery
Recovering at the liquid line captures refrigerant already in subcooled liquid form, which speeds recovery, while the discharge service valve holds superheated high-pressure vapor, making recovery slower and less efficient.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 50 - Servicing Commercial Systems, Page 1233 (20th ed.: Page 1500)Duct leakage tested before air handler installedvsDuct leakage tested with air handler installed
Per the IECC, maximum leakage is 3 cfm per 100 ft² of conditioned space when tested before the air handler is installed, versus 4 cfm per 100 ft² when tested with it installed.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 31 - Ventilation System Service, Page 703 (Section 31.1.5) (20th ed.: Page 793)ACCA Manual DvsACCA Manual J / Manual S
Per IMC 2024 Section 603.2, Manual D is an accepted duct sizing method for ducts within a single dwelling unit, while Manual J is for load calculations and Manual S is for equipment selection (neither sizes ducts).
IMC 2024 Section 603.2Key Terms
Velocity pressure Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 28 - Air Movement and Measurement, Page 630 (20th ed.: Page 710)
The difference between total air pressure and static air pressure, such that total pressure equals static pressure plus velocity pressure; a pitot tube's inner tube reads total pressure and its side-holed outer tube reads static pressure.
Distributor Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 45 - Commercial Metering Devices and Valves, Page 1088 (Section 45.1.4) (20th ed.: Pages 490-491)
A device at the metering device outlet that splits refrigerant into several shorter parallel evaporator circuits, reducing pressure drop and giving more consistent coil temperature.
Draft Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 34 - Oil-Fired Heating Systems, Page 796 (20th ed.: Page 1155)
The movement of flue gas, measured with a draft gauge in inches of water column, indicating how quickly flue gases pass through the heat exchanger.
K-value (thermal conductivity) Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 32 - Heating and Cooling Loads, Page 717 (20th ed.: Page 986)
The amount of heat that will pass through one square foot of a material one inch thick, in one hour, with a 1°F temperature difference between sides (Btu·in/hr·ft²·°F).
Zeotropic blend / fractionation Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 12 - Working with Refrigerants, Page 243 (20th ed.: Page 259)
A 400-series refrigerant blend (such as R-410A) whose components vaporize at different temperatures, so it must always be liquid charged; vapor charging causes fractionation, with the lowest boiling point component entering the system first.
PTC relay Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 346 (Section 17.5) (20th ed.: Chapter 16, Section 16.3.5 — Positive Temperature Coefficient Relays)
A positive temperature coefficient thermistor relay wired in parallel with the run capacitor that has a low resistance of 3 Ω to 12 Ω when cool (so start current takes that path) and rises to 10 kΩ–20 kΩ when heated, forcing current through the run capacitor.
Potential relay Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 339 ("Potential Relays") (20th ed.: Chapter 16, Section 16.3.5 — Potential Relays)
A starting relay that actuates on the counter electromotive force (cemf) induced in the start winding; at the pickup voltage (about three-fourths of rated speed) its coil energizes and opens the normally closed contacts to drop out the start capacitor.
Current relay terminals L, M, S Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 339 (Section 17.4.5) (20th ed.: Chapter 16, Section 16.3.5 — Current Relays)
On a current relay, L is line voltage, M is the main (run) winding, and S is the start winding; a normally open contact lies between L and S and the relay coil between L and M.
High-pressure motor control Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 334 ("High-Pressure Motor Controls") (20th ed.: Chapter 16, Section 16.3.4 — High-Pressure Motor Controls)
A safety control usually set to cut out at 20% above normal head pressure to protect the compressor from high pressure and temperature and the motor from overheating and overloading.
Multipurpose fuse Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 347 (Section 17.5.1) (20th ed.: Chapter 16, Section 16.4.1)
A fuse combining fast-acting and time-delay characteristics: it will not blow on small short-duration overloads such as motor starting but blows immediately on overloads over 500% of its maximum current rating.
Current-limiting fuse Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 347 (Section 17.5.1) (20th ed.: Chapter 16, Section 16.4.1)
A fuse using temperature-sensitive resistors that open when current exceeds the limit and the fuse heats up, then close again when cooled, preventing motor current from exceeding rated locked rotor amperage.
Impedance Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 354 (Section 17.6.1) (20th ed.: Section 16.5.2 (DDC System Components — Controlled Devices, Lockout Relay))
The opposition to the flow of alternating current in an ac circuit; a lockout relay is a high-impedance relay whose coil prevents enough current from reaching the compressor relay coil to energize it when a safety control has opened.
Overload (circuit) Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 14 - Electrical Power, Page 283 (Section 14.3.3) (20th ed.: Section 13.3.3 (Overload))
A condition in which too much current flows through a circuit, caused by an incorrect power supply, equipment failure, too many loads connected in parallel, or electromechanical equipment operating under strained conditions.
Sequencer Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 35 - Electric Heating Systems, Page 834 (20th ed.: Pages 1196 and 1205)
A device in an electric furnace that opens and closes contacts on a time delay (typically about 30 seconds apart) to energize heating elements one at a time and minimize initial current draw.
Crankcase heater Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 43 - Commercial Compressors, Page 1045 (Section 43.1) (20th ed.: Page 467)
An electric heating element on or in a compressor that keeps it warm during the Off cycle so refrigerant does not condense in the crankcase, preventing liquid slugging or a flooded start.
Overfiring Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 34 - Oil-Fired Heating Systems, Page 795 (Section 34.3.2) (20th ed.: Page 1154)
A condition in which a heating system creates too much heat, often from installing a higher-capacity burner nozzle than the original, so excess heat escapes up the flue and stack temperature rises.
Category IV furnace Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 33 - Gas-Fired Heating Systems, Page 776 (20th ed.: Page 1134)
A positive-pressure venting, condensing furnace whose flue gas temperature is below 140°F (60°C) — under its dew point — using a secondary heat exchanger and PVC vent piping.
cfm50 / duct leakage test pressure Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 31 - Ventilation System Service, Page 702 (20th ed.: Page 791)
cfm50 is the airflow through a blower door fan with indoor pressure held at −50 Pa WRT outdoors (used to compute ACH50); by contrast a duct leakage test seals registers and pressurizes ducts to +25 Pa WRT the conditioned space, giving cfm25.
Refrigerant quality Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 51 - Understanding Heat Loads and System Thermodynamics, Page 1273 (20th ed.: Page 1372)
On a pressure-enthalpy diagram, the portion of refrigerant mass that is vapor — a 10% quality means 10% vapor and 90% liquid.
Panned joist space Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 30 - Air Distribution, Page 672 (20th ed.: Page 755)
A basement return-air branch duct construction method using the joists and floorboards as three sides of the duct.
Formulas to Know
Ohm's law (resistance and current)
R = E ÷ I and I = E ÷ R; e.g., 240 V ÷ 10 A = 24 Ω, and 24 V ÷ 8 Ω = 3 A (in a series circuit the same current flows through every load)Watt's law (single-phase power)
P = I × E; e.g., 20 A × 120 V = 2400 W; 15 A × 240 V = 3600 W; 8 A × 240 V = 1920 WControl differential
Differential = difference between cut-out and cut-in (always subtract the lower value from the higher): heating = cut-out − cut-in (e.g., 74°F − 68°F = 6°F); cooling = cut-in − cut-out (e.g., 25°F − 15°F = 10°F)Subcooling
Subcooling = condensing (saturation) temperature at operating pressure − actual measured liquid temperature; e.g., 212°F − 190°F = 22°FDuct air velocity from velocity pressure (pitot tube)
V = 4005 × √Pv (Pv in inches of water); e.g., 4005 × √0.25 = 4005 × 0.5 ≈ 2003 ft/minAir changes per hour
ACH = (airflow in cfm × 60 min) ÷ room volume in cubic feetBtu/hr to kilowatts for electric heat sizing
kW = Btu/hr ÷ 3,413; e.g., 50,000 ÷ 3,413 = 14.65 kWCoefficient of performance from a pressure-enthalpy diagram
COP = refrigeration effect ÷ heat of compression = (compressor inlet h − evaporator inlet h) ÷ (compressor outlet h − compressor inlet h); e.g., (179 − 116) ÷ (198 − 179) = 63 ÷ 19 = 3.32:1Total equivalent length and duct friction loss
Total equivalent length = sum of straight segments + elbow equivalent lengths (e.g., 28 + 22 + 15 + 2×25 = 115 ft); Friction loss = (total equivalent length ÷ 100) × friction rate = (115/100) × 0.10 = 0.115 in. WCMinimum circuit ampacity (MCA)
MCA = 1.25 × largest motor FLA/RLA + sum of other loads; e.g., 1.25 × 24.0 A + 2.1 A = 32.1 A (do not apply the 125% factor to both loads)