Page 1 of 151
STAR HVAC Mastery Exam–ACTUAL QUESTIONS
AND ANSWERS LATEST UPDATE THIS YEAR
STAR HVACR Mastery certification is an ANSI-accredited, closed-book exam administered by NITC.
Candidates must have at least five years of experience (or completion of a recognized apprenticeship)
and must answer at least 158 of 199 questions correctly (≈82%) to pass . Recertification is required
every five years via a 50-question open-book exam .
Summarized Exam Coverage (Point Form)
Mechanical Principles (Refrigeration & Thermodynamics)
• First Law of Thermodynamics: Energy cannot be created or destroyed—only transferred or
converted (conservation of energy) .
• Second Law: Heat flows naturally from warmer to cooler bodies; entropy increases.
• Sensible Heat: Heat that changes temperature without changing phase (e.g., warming air) .
• Latent Heat: Heat absorbed or released during a phase change (e.g., evaporation, condensation)
without temperature change .
• Refrigeration Cycle Components: Compressor (raises pressure/temperature), condenser (rejects
heat), expansion device (drops pressure), evaporator (absorbs heat) .
• Pressure-Temperature Relationship: Saturation curves on P-T charts and P-H diagrams show the
boiling/condensing point at a given pressure .
• Superheat: Vapor temperature above saturation temperature at evaporator outlet—ensures no
liquid enters compressor .
• Subcooling: Liquid temperature below saturation temperature at condenser outlet—increases
system capacity .
• Gas Laws: Boyle’s Law (P₁V₁ = P₂V₂ at constant T), Charles’s Law (V₁/T₁ = V₂/T₂ at constant P),
Dalton’s Law (total pressure = sum of partial pressures).
• Compressor Types: Scroll, reciprocating, rotary, screw, centrifugal.
• Refrigerant Properties: Ozone Depletion Potential (ODP), Global Warming Potential (GWP),
saturation curves, oil return compatibility.
Electrical Principles
• Ohm’s Law: V = I × R, I = V / R, R = V / I .
• Power Formula: P = V × I (watts), S = V × I (VA for apparent power) .
• Series Circuits: Voltage divides, current is constant, total resistance = sum of resistances .
• Parallel Circuits: Voltage constant across branches, current divides, total resistance = R/n (for
equal resistors) .
• Series-Parallel Networks: Total resistance always greater than the smallest resistor .
• Three-Phase Systems: Phase voltage (line to neutral) vs. line voltage (line to line) in wye vs.
delta configurations .
• Motors: PSC (Permanent Split Capacitor), ECM (Electronically Commutated Motor),
shaded-pole, three-phase.
• Start Capacitor: Provides phase shift for starting torque .
• Thermal Overload Relay: Protects motor from overheating by opening circuit when
current/temperature exceeds limit .
• Transformers: Step-down (e.g., 120V to 24V control circuit) .
• Phase Imbalance: Voltage imbalance >2% reduces motor efficiency and causes overheating .
Controls & Instrumentation
, Page 2 of 151
• TXV (Thermostatic Expansion Valve): Regulates refrigerant flow to maintain set superheat .
• DDC (Direct Digital Control): Sensors provide real-time data to controllers; BACnet is common
protocol .
• PID Controller: Combines proportional (present error), integral (past error), and derivative
(future trend) to determine output .
• Sensors: Thermocouples (voltage from dissimilar metals), thermistors (resistance), pressure
transducers.
• Psychrometer: Measures wet-bulb and dry-bulb temperatures to determine humidity .
• Manometer: Measures pressure (e.g., static pressure in ducts, refrigerant pressure) .
• Halogen/Electronic Leak Detector: Detects refrigerant leaks .
• Ultrasonic Leak Detector: Best for small, low-pressure refrigerant leaks .
• Micron Gauge: Measures deep vacuum during system evacuation .
• Sight Glass: Observes refrigerant condition (bubbles indicate low charge or non-condensables).
Air Conditioning & Refrigeration
• Standard Airflow: 400 CFM per ton of cooling .
• Vapor-Compression Cycle: Compressor → Condenser → Expansion Valve → Evaporator →
Return to Compressor.
• Charging Methods: Weighing cylinder before/after charging is most accurate .
• Evacuation: Removes air and moisture; target <500 microns (deep vacuum ≤100 microns for
commercial) .
• Filter-Drier: Removes moisture and contaminants; contains desiccant .
• Condenser Types: Air-cooled, water-cooled, evaporative.
• Evaporator Types: Dry expansion, flooded, fin-and-tube.
• Head Pressure: High-side pressure; affected by condenser cleanliness and airflow .
• Suction Pressure: Low-side pressure; affected by evaporator load, TXV operation, and charge.
• Subcooling Measurement: Liquid line temperature minus saturation temperature at condenser
outlet.
• Superheat Measurement: Suction line temperature minus saturation temperature at
evaporator outlet.
• Overcharge Symptoms: High head pressure, high discharge temperature, low cooling capacity .
• Undercharge Symptoms: Low suction pressure, low head pressure, low superheat (or high
superheat depending on system), bubbles in sight glass.
Heating Systems
• AFUE (Annual Fuel Utilization Efficiency): Measures furnace/boiler efficiency over a heating
season .
• Furnace Sequence: Ignition → Combustion → Fan → Safety lockout .
• Flame Sensor: Detects flame presence; shuts off gas if flame is absent .
• High-Limit Switch: Shuts off furnace at unsafe temperatures (overheating protection) .
• Expansion Tank (Boiler): Compensates for water volume changes due to temperature
fluctuations .
• Safety Valve (Boiler): Releases pressure when system exceeds preset limit .
• Induced-Draft Fan: Uses venturi effect to draw flue gases through furnace .
• Heat Pump: Provides both heating and cooling via reversing valve that switches refrigerant
flow .
Ventilation, Ductwork & Psychrometrics
• Psychrometric Chart: Relates dry-bulb, wet-bulb, dew point, relative humidity, enthalpy, and
specific humidity.
, Page 3 of 151
• Specific Humidity (Mixing Ratio): Mass of water vapor per mass of dry air (grains per pound) .
• Dew Point Temperature: Temperature at which water vapor condenses at constant pressure .
• Relative Humidity: Ratio of current water vapor to maximum possible at given temperature .
• Sensible Heat Ratio (SHR): Sensible load ÷ Total load; indicates proportion of load met by
sensible cooling .
• Air-Side Economizer: Uses outdoor air for free cooling when conditions permit .
• Static Pressure: Resistance to airflow caused by duct friction and fittings; measured
perpendicular to flow .
• Velocity Pressure: Kinetic energy of moving air (½ ρ V²) .
• VAV (Variable Air Volume) Box: Modulates airflow to meet zone temperature setpoints .
• MERV Rating: Minimum Efficiency Reporting Value; higher MERV = finer filtration (MERV 13
captures 0.3-1 μm particles) .
• Plenum: Air distribution box connected to ductwork .
Applied Mathematics & Blueprint Reading
• Temperature Conversion: °C = (°F – 32) × 5/9; °F = (°C × 9/5) + 32 .
• Absolute Pressure: P_abs = P_gauge + P_atm (14.7 psi at sea level) .
• Fan Laws: Airflow ∝ Speed; Pressure ∝ Speed²; Power ∝ Speed³.
• Voltage Drop: Directly proportional to conductor length .
• Resistor Networks: Series: R_total = R₁ + R₂ + … ; Parallel: 1/R_total = 1/R₁ + 1/R₂ + … .
• Power Calculation: Apparent power (VA) = V × I .
• Refrigerant Mass Flow: Measured in pounds per hour (lb/h) .
• Thermodynamic Work: Work = Force × Distance; Power = Work ÷ Time.
Lifting, Rigging & Safety
• Lockout/Tagout (LOTO): Prevents accidental energization during maintenance .
• SWL (Safe Working Load): Crane capacity must be at least 1.5× the actual weight for overhead
lifts .
• Pressure Relief Valve: Required on all HVACR refrigerant recovery equipment to prevent
over-pressurization .
• NEC Requirements: Dedicated motor overload protection; minimum grounding electrode
conductor size for 100-amp service is 8 AWG copper .
• Refrigerant Safety: A2L (mildly flammable) require ventilation and elimination of ignition
sources during recovery .
• EPA Section 608: Type III classification applies to high-pressure refrigerants (R-410A) .
Environmental Regulations & Refrigerants
• Ozone Depleting Substances (ODS): R-22 (HCFC) has ODP >0 and is being phased out .
• HFCs (e.g., R-410A, R-134a, R-404A): ODP = 0 but high GWP; subject to phase-down .
• Natural Refrigerants: R-717 (ammonia) is a natural refrigerant with zero ODP and zero GWP .
• CO₂ (R-744) as Secondary Fluid: Zero ODP and low GWP; used in supermarket cascade systems .
• Recovery, Recycle, Reclaim: EPA-mandated processes to prevent refrigerant release to
atmosphere.
250 Scenario-Based MCQs with Rationales
Domain 1: Mechanical Principles & Thermodynamics (1-40)
, Page 4 of 151
1. Which law of thermodynamics states that energy cannot be created or destroyed, only transferred
or converted?
A. Zeroth Law
B. First Law
C. Second Law
D. Third Law
Answer: B
Rationale: The First Law of Thermodynamics is the conservation of energy principle, indicating that total
energy in an isolated system remains constant; this is the foundation for energy balance calculations in
HVACR systems .
2. During a refrigeration cycle, which component is responsible for raising the refrigerant’s pressure
and temperature before it enters the condenser?
A. Evaporator
B. Condenser
STAR HVAC Mastery Exam–ACTUAL QUESTIONS
AND ANSWERS LATEST UPDATE THIS YEAR
STAR HVACR Mastery certification is an ANSI-accredited, closed-book exam administered by NITC.
Candidates must have at least five years of experience (or completion of a recognized apprenticeship)
and must answer at least 158 of 199 questions correctly (≈82%) to pass . Recertification is required
every five years via a 50-question open-book exam .
Summarized Exam Coverage (Point Form)
Mechanical Principles (Refrigeration & Thermodynamics)
• First Law of Thermodynamics: Energy cannot be created or destroyed—only transferred or
converted (conservation of energy) .
• Second Law: Heat flows naturally from warmer to cooler bodies; entropy increases.
• Sensible Heat: Heat that changes temperature without changing phase (e.g., warming air) .
• Latent Heat: Heat absorbed or released during a phase change (e.g., evaporation, condensation)
without temperature change .
• Refrigeration Cycle Components: Compressor (raises pressure/temperature), condenser (rejects
heat), expansion device (drops pressure), evaporator (absorbs heat) .
• Pressure-Temperature Relationship: Saturation curves on P-T charts and P-H diagrams show the
boiling/condensing point at a given pressure .
• Superheat: Vapor temperature above saturation temperature at evaporator outlet—ensures no
liquid enters compressor .
• Subcooling: Liquid temperature below saturation temperature at condenser outlet—increases
system capacity .
• Gas Laws: Boyle’s Law (P₁V₁ = P₂V₂ at constant T), Charles’s Law (V₁/T₁ = V₂/T₂ at constant P),
Dalton’s Law (total pressure = sum of partial pressures).
• Compressor Types: Scroll, reciprocating, rotary, screw, centrifugal.
• Refrigerant Properties: Ozone Depletion Potential (ODP), Global Warming Potential (GWP),
saturation curves, oil return compatibility.
Electrical Principles
• Ohm’s Law: V = I × R, I = V / R, R = V / I .
• Power Formula: P = V × I (watts), S = V × I (VA for apparent power) .
• Series Circuits: Voltage divides, current is constant, total resistance = sum of resistances .
• Parallel Circuits: Voltage constant across branches, current divides, total resistance = R/n (for
equal resistors) .
• Series-Parallel Networks: Total resistance always greater than the smallest resistor .
• Three-Phase Systems: Phase voltage (line to neutral) vs. line voltage (line to line) in wye vs.
delta configurations .
• Motors: PSC (Permanent Split Capacitor), ECM (Electronically Commutated Motor),
shaded-pole, three-phase.
• Start Capacitor: Provides phase shift for starting torque .
• Thermal Overload Relay: Protects motor from overheating by opening circuit when
current/temperature exceeds limit .
• Transformers: Step-down (e.g., 120V to 24V control circuit) .
• Phase Imbalance: Voltage imbalance >2% reduces motor efficiency and causes overheating .
Controls & Instrumentation
, Page 2 of 151
• TXV (Thermostatic Expansion Valve): Regulates refrigerant flow to maintain set superheat .
• DDC (Direct Digital Control): Sensors provide real-time data to controllers; BACnet is common
protocol .
• PID Controller: Combines proportional (present error), integral (past error), and derivative
(future trend) to determine output .
• Sensors: Thermocouples (voltage from dissimilar metals), thermistors (resistance), pressure
transducers.
• Psychrometer: Measures wet-bulb and dry-bulb temperatures to determine humidity .
• Manometer: Measures pressure (e.g., static pressure in ducts, refrigerant pressure) .
• Halogen/Electronic Leak Detector: Detects refrigerant leaks .
• Ultrasonic Leak Detector: Best for small, low-pressure refrigerant leaks .
• Micron Gauge: Measures deep vacuum during system evacuation .
• Sight Glass: Observes refrigerant condition (bubbles indicate low charge or non-condensables).
Air Conditioning & Refrigeration
• Standard Airflow: 400 CFM per ton of cooling .
• Vapor-Compression Cycle: Compressor → Condenser → Expansion Valve → Evaporator →
Return to Compressor.
• Charging Methods: Weighing cylinder before/after charging is most accurate .
• Evacuation: Removes air and moisture; target <500 microns (deep vacuum ≤100 microns for
commercial) .
• Filter-Drier: Removes moisture and contaminants; contains desiccant .
• Condenser Types: Air-cooled, water-cooled, evaporative.
• Evaporator Types: Dry expansion, flooded, fin-and-tube.
• Head Pressure: High-side pressure; affected by condenser cleanliness and airflow .
• Suction Pressure: Low-side pressure; affected by evaporator load, TXV operation, and charge.
• Subcooling Measurement: Liquid line temperature minus saturation temperature at condenser
outlet.
• Superheat Measurement: Suction line temperature minus saturation temperature at
evaporator outlet.
• Overcharge Symptoms: High head pressure, high discharge temperature, low cooling capacity .
• Undercharge Symptoms: Low suction pressure, low head pressure, low superheat (or high
superheat depending on system), bubbles in sight glass.
Heating Systems
• AFUE (Annual Fuel Utilization Efficiency): Measures furnace/boiler efficiency over a heating
season .
• Furnace Sequence: Ignition → Combustion → Fan → Safety lockout .
• Flame Sensor: Detects flame presence; shuts off gas if flame is absent .
• High-Limit Switch: Shuts off furnace at unsafe temperatures (overheating protection) .
• Expansion Tank (Boiler): Compensates for water volume changes due to temperature
fluctuations .
• Safety Valve (Boiler): Releases pressure when system exceeds preset limit .
• Induced-Draft Fan: Uses venturi effect to draw flue gases through furnace .
• Heat Pump: Provides both heating and cooling via reversing valve that switches refrigerant
flow .
Ventilation, Ductwork & Psychrometrics
• Psychrometric Chart: Relates dry-bulb, wet-bulb, dew point, relative humidity, enthalpy, and
specific humidity.
, Page 3 of 151
• Specific Humidity (Mixing Ratio): Mass of water vapor per mass of dry air (grains per pound) .
• Dew Point Temperature: Temperature at which water vapor condenses at constant pressure .
• Relative Humidity: Ratio of current water vapor to maximum possible at given temperature .
• Sensible Heat Ratio (SHR): Sensible load ÷ Total load; indicates proportion of load met by
sensible cooling .
• Air-Side Economizer: Uses outdoor air for free cooling when conditions permit .
• Static Pressure: Resistance to airflow caused by duct friction and fittings; measured
perpendicular to flow .
• Velocity Pressure: Kinetic energy of moving air (½ ρ V²) .
• VAV (Variable Air Volume) Box: Modulates airflow to meet zone temperature setpoints .
• MERV Rating: Minimum Efficiency Reporting Value; higher MERV = finer filtration (MERV 13
captures 0.3-1 μm particles) .
• Plenum: Air distribution box connected to ductwork .
Applied Mathematics & Blueprint Reading
• Temperature Conversion: °C = (°F – 32) × 5/9; °F = (°C × 9/5) + 32 .
• Absolute Pressure: P_abs = P_gauge + P_atm (14.7 psi at sea level) .
• Fan Laws: Airflow ∝ Speed; Pressure ∝ Speed²; Power ∝ Speed³.
• Voltage Drop: Directly proportional to conductor length .
• Resistor Networks: Series: R_total = R₁ + R₂ + … ; Parallel: 1/R_total = 1/R₁ + 1/R₂ + … .
• Power Calculation: Apparent power (VA) = V × I .
• Refrigerant Mass Flow: Measured in pounds per hour (lb/h) .
• Thermodynamic Work: Work = Force × Distance; Power = Work ÷ Time.
Lifting, Rigging & Safety
• Lockout/Tagout (LOTO): Prevents accidental energization during maintenance .
• SWL (Safe Working Load): Crane capacity must be at least 1.5× the actual weight for overhead
lifts .
• Pressure Relief Valve: Required on all HVACR refrigerant recovery equipment to prevent
over-pressurization .
• NEC Requirements: Dedicated motor overload protection; minimum grounding electrode
conductor size for 100-amp service is 8 AWG copper .
• Refrigerant Safety: A2L (mildly flammable) require ventilation and elimination of ignition
sources during recovery .
• EPA Section 608: Type III classification applies to high-pressure refrigerants (R-410A) .
Environmental Regulations & Refrigerants
• Ozone Depleting Substances (ODS): R-22 (HCFC) has ODP >0 and is being phased out .
• HFCs (e.g., R-410A, R-134a, R-404A): ODP = 0 but high GWP; subject to phase-down .
• Natural Refrigerants: R-717 (ammonia) is a natural refrigerant with zero ODP and zero GWP .
• CO₂ (R-744) as Secondary Fluid: Zero ODP and low GWP; used in supermarket cascade systems .
• Recovery, Recycle, Reclaim: EPA-mandated processes to prevent refrigerant release to
atmosphere.
250 Scenario-Based MCQs with Rationales
Domain 1: Mechanical Principles & Thermodynamics (1-40)
, Page 4 of 151
1. Which law of thermodynamics states that energy cannot be created or destroyed, only transferred
or converted?
A. Zeroth Law
B. First Law
C. Second Law
D. Third Law
Answer: B
Rationale: The First Law of Thermodynamics is the conservation of energy principle, indicating that total
energy in an isolated system remains constant; this is the foundation for energy balance calculations in
HVACR systems .
2. During a refrigeration cycle, which component is responsible for raising the refrigerant’s pressure
and temperature before it enters the condenser?
A. Evaporator
B. Condenser
