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Nevada C-21B Air Conditioning Contractor
Practice Exam 300 Questions with Correct
Answers and Explanations in Italic.
EXAM OVERVIEW
Category Details License Type C-21B Air Conditioning Contractor Governing Body Nevada State Contractors Board (NSCB) Legal Authority NRS 624 (Nevada Revised Statutes) Experience Required 4 years in the trade Exams Required Trade-specific (C-21B) + Business and Law (Contractor Management Survey)
SECTION 1: FUNDAMENTALS OF AIR CONDITIONING
Question 1: Which of the following best describes the primary function of an air conditioning system as defined for a C-21B contractor in Nevada? A) To provide complete building automation B) To regulate indoor temperature and humidity C) To serve as a primary heating source D) To replace mechanical ventilation systems Correct Answer: B) To regulate indoor temperature and humidity Explanation: Under NAC 624.380, the C-21B subclassification specifically covers equipment that uses evaporation, refrigeration, boilers, or combustion for the control of air temperatures, including humidity controls.
Question 2: What is the primary difference between sensible heat and latent heat in HVAC calculations? A) Sensible heat changes temperature, latent heat changes phase B) Sensible heat changes pressure, latent heat changes volume C) Sensible heat is measured in BTU/hr, latent heat in kW D) Sensible heat is only in cooling, latent heat only in heating Correct Answer: A) Sensible heat changes temperature, latent heat changes phase Explanation: Sensible heat results in a temperature change without a phase change, while latent heat involves a phase change (e.g., condensation or evaporation) at constant temperature. Question 3: What is the term for heat that changes the temperature of a substance without changing its physical state? A) Latent heat B) Superheat C) Subcooling D) Sensible heat Correct Answer: D) Sensible heat Explanation: Sensible heat is the energy added or removed that causes a change in temperature. Latent heat causes a phase change (melting, boiling) without a temperature change. Question 4: Which psychrometric property is directly read from the horizontal axis of a psychrometric chart? A) Relative humidity B) Specific humidity
Question 7: Which component is primarily responsible for reducing the pressure of the refrigerant before it enters the evaporator? A) Compressor B) Condenser C) Expansion device D) Receiver Correct Answer: C) Expansion device Explanation: The expansion device (thermal expansion valve, capillary tube, or fixed orifice) creates a pressure drop, allowing the refrigerant to evaporate at low pressure in the evaporator. Question 8: What does an "A1" refrigerant classification signify according to ASHRAE? A) Low toxicity, high flammability B) Low toxicity, non-flammable C) High toxicity, non-flammable D) High toxicity, high flammability Correct Answer: B) Low toxicity, non-flammable Explanation: ASHRAE "A1" denotes refrigerants that are mildly toxic (Class A) and non- flammable (Class 1), such as R-410A. Question 9: Which refrigerant is commonly used in modern residential air conditioning systems? A) R- 22 B) R-410A C) R- 12 D) Ammonia Correct Answer: B) R-410A
Explanation: R-410A is widely used today due to its efficiency and compliance with environmental regulations. R-22 is being phased out due to ozone depletion concerns. Question 10: Which refrigerant has the lowest Global Warming Potential (GWP) among the commonly used HVAC refrigerants? A) R-410A B) R- 22 C) R- 32 D) R-404A Correct Answer: C) R- 32 Explanation: R-32 has a GWP of about 675, significantly lower than R-410A (~2088) and R-404A (~3900). It offers higher efficiency and lower environmental impact.
SECTION 2: REFRIGERATION CYCLE COMPONENTS
Question 11: What is the primary function of the evaporator coil in an air conditioning system? A) To compress refrigerant B) To absorb heat from indoor air C) To expel heat to the outside D) To control refrigerant flow Correct Answer: B) To absorb heat from indoor air Explanation: The evaporator coil contains cold refrigerant that absorbs heat from the warm indoor air blowing over it, cooling the air before it is circulated back into the space. Question 12: Which part of the AC system discharges the absorbed heat to the outdoor environment?
Question 15: Which of the following is the correct sequence for refrigerant flow in a standard vapor-compression cycle? A) Compressor → Condenser → Expansion valve → Evaporator B) Evaporator → Compressor → Condenser → Expansion valve C) Condenser → Compressor → Evaporator → Expansion valve D) Expansion valve → Evaporator → Compressor → Condenser Correct Answer: A) Compressor → Condenser → Expansion valve → Evaporator Explanation: The refrigerant leaves the compressor as high-pressure vapor, condenses in the condenser, expands through the expansion valve, then evaporates in the evaporator. Question 16: The amount of heat a refrigerant absorbs in the evaporator is known as: A) Latent heat of vaporization B) Sensible heat C) Refrigerating effect D) Superheat Correct Answer: C) Refrigerating effect Explanation: The refrigerating effect is the amount of heat absorbed by the refrigerant in the evaporator per unit of refrigerant circulated. Question 17: Which type of compressor is most common in modern residential split systems? A) Screw compressor B) Scroll compressor C) Centrifugal compressor D) Reciprocating compressor Correct Answer: B) Scroll compressor
Explanation: Scroll compressors are reliable, efficient, and have fewer moving parts than reciprocating types. They have become the industry standard for residential HVAC applications. Question 18: The superheat of a refrigeration system is defined as: A) The temperature of the refrigerant leaving the condenser B) The difference between the actual temperature of the refrigerant vapor and its saturation temperature at the same pressure C) The temperature of the liquid refrigerant below its saturation point D) The outdoor ambient temperature plus the heat of compression Correct Answer: B) The difference between the actual temperature of the refrigerant vapor and its saturation temperature at the same pressure Explanation: Superheat is the difference between the actual temperature of the refrigerant vapor and its saturation temperature (boiling point) at the same pressure. It ensures no liquid enters the compressor. Question 19: Subcooling in a refrigeration system refers to: A) The temperature of the refrigerant vapor above its saturation point B) The temperature of the liquid refrigerant below its saturation point C) The temperature difference across the evaporator D) The amount of heat absorbed in the condenser Correct Answer: B) The temperature of the liquid refrigerant below its saturation point Explanation: Subcooling is the amount of heat removed from the liquid refrigerant after it has condensed, lowering its temperature below the saturation temperature. This improves system efficiency.
Correct Answer: B) Psychrometer Explanation: A psychrometer measures wet-bulb and dry-bulb temperatures, allowing calculation of relative humidity and dew point. Question 23: The "sensible heat ratio" (SHR) is defined as: A) Latent heat ÷ Total heat B) Sensible heat ÷ Total heat C) Total heat ÷ Latent heat D) Sensible heat ÷ Latent heat Correct Answer: B) Sensible heat ÷ Total heat Explanation: SHR = sensible heat load divided by the total (sensible + latent) load. It indicates the proportion of the total cooling load that is sensible cooling. Question 24: A psychrometric chart is used to determine which of the following? A) Refrigerant pressure-temperature relationships B) Air properties including temperature, humidity, and enthalpy C) Duct friction losses D) Electrical load calculations Correct Answer: B) Air properties including temperature, humidity, and enthalpy Explanation: A psychrometric chart graphically represents the thermodynamic properties of moist air, including dry-bulb temperature, wet-bulb temperature, relative humidity, humidity ratio, and enthalpy.
SECTION 4: LOAD CALCULATIONS AND SIZING
Question 25: Manual J is used to calculate which of the following?
A) Commercial ventilation rates B) Residential heating and cooling loads C) Duct friction losses D) Refrigerant charge amounts Correct Answer: B) Residential heating and cooling loads Explanation: Manual J (ACC-A) provides procedures for determining the heating and cooling loads of residential buildings. Question 26: What is the purpose of performing a "Manual J" load calculation? A) To determine the price of the ductwork B) To determine the correct size and capacity of the AC unit C) To calculate the voltage drop for the thermostat wire D) To estimate the labor hours for installation Correct Answer: B) To determine the correct size and capacity of the AC unit Explanation: Manual J is the ACCA standard for residential load calculations. It analyzes factors such as square footage, insulation, windows, orientation, and occupancy to determine the precise heating and cooling load. Question 27: When performing a Manual N calculation for a commercial building, which factor is NOT typically considered? A) Internal equipment heat gains B) Solar heat gain through glazing C) Occupant clothing insulation values D) Building orientation and shading devices Correct Answer: C) Occupant clothing insulation values Explanation: Occupant clothing insulation (clo values) is a residential consideration; commercial calculations focus on equipment, lighting, and occupancy density.
Explanation: The industry standard is approximately 400 CFM per ton of cooling to ensure adequate airflow and proper coil performance. Question 31: Which of the following is the most accurate method for determining a building's cooling load due to solar gain through windows? A) Using a fixed 150 BTU/hr per ft² factor B) Applying the SHGC (Solar Heat Gain Coefficient) value in a heat-gain calculation C) Measuring interior temperature rise during midday D) Assuming all windows transmit 100% solar radiation Correct Answer: B) Applying the SHGC (Solar Heat Gain Coefficient) value in a heat-gain calculation Explanation: SHGC quantifies the fraction of solar radiation transmitted through glazing as heat, allowing precise load calculations.
SECTION 5: DUCT DESIGN AND AIRFLOW
Question 32: Static pressure in a duct system is measured in: A) Pascals (Pa) only B) Inches of water column (in wc) C) Pounds per square foot (psf) D) Both B and C are acceptable units Correct Answer: D) Both B and C are acceptable units Explanation: Static pressure is commonly expressed in inches of water column (in wc) or pounds per square foot (psf); both are accepted industry units. Question 33: When designing a supply duct for a single-zone system, the velocity should generally not exceed:
A) 400 ft/min B) 600 ft/min C) 800 ft/min D) 1000 ft/min Correct Answer: B) 600 ft/min Explanation: To limit noise and pressure loss, supply duct velocities are typically limited to 600 ft/min for most residential/commercial applications. Question 34: The primary function of a plenum in an HVAC system is to: A) Filter air before it enters the system B) Regulate humidity in ductwork C) Distribute air from the HVAC unit to multiple branches D) Provide a space for electrical wiring Correct Answer: C) Distribute air from the HVAC unit to multiple branches Explanation: A plenum serves as a central distribution chamber for conditioned air, allowing it to flow into multiple duct branches efficiently. Question 35: What is the effect of excessive static pressure in a duct system? A) Increased airflow B) Reduced fan energy consumption C) Higher noise levels and reduced efficiency D) Lower coil temperature Correct Answer: C) Higher noise levels and reduced efficiency Explanation: High static pressure forces the fan to work harder, causing noise and efficiency loss.
SECTION 6: REFRIGERANTS AND EPA REGULATIONS
Question 39: Section 608 of the EPA regulations primarily addresses which of the following? A) Energy efficiency standards for HVAC equipment B) Safe handling and disposal of refrigerants C) Minimum ventilation rates for commercial buildings D) Electrical safety requirements Correct Answer: B) Safe handling and disposal of refrigerants Explanation: EPA Section 608 regulates the handling, recovery, recycling, and disposal of refrigerants to protect the ozone layer. Question 40: According to the Clean Air Act, who is responsible for the proper handling and recovery of refrigerants? A) The equipment manufacturer only B) The building owner C) EPA-certified technicians D) The local utility company Correct Answer: C) EPA-certified technicians Explanation: The EPA's Section 608 regulations mandate that any technician who performs maintenance, service, repair, or disposal of air conditioning and refrigeration equipment must be certified to handle refrigerants. Question 41: Under EPA Section 608, which certification is required to service both high-pressure (R-410A) and low-pressure (R-22) refrigerants? A) Type I only B) Type II only
C) Type III only D) Universal Correct Answer: D) Universal Explanation: The Universal certification permits handling of all refrigerant types, including high- and low-pressure systems. Question 42: Which refrigerant is classified as a Class III ozone-depleting substance? A) R-410A B) R- 22 C) R-134a D) R-404A Correct Answer: B) R- 22 Explanation: R-22 (chlorodifluoromethane) is a Class III ozone-depleting refrigerant and is being phased out. Question 43: Which of the following would be a direct violation of EPA refrigerant regulations? A) Using a certified recovery machine B) Releasing R-410A intentionally to the atmosphere C) Selling recovered refrigerant to a licensed reclaimer D) Tagging a refrigerant cylinder with the refrigerant type Correct Answer: B) Releasing R-410A intentionally to the atmosphere Explanation: The Clean Air Act prohibits the deliberate venting of refrigerants to the atmosphere. All refrigerants must be recovered using certified equipment.
Correct Answer: B) To change the direction of refrigerant flow for heating or cooling mode Explanation: The reversing valve is a four-way directional valve that switches the functions of the evaporator and condenser coils, allowing a heat pump to provide both cooling and heating. Question 47: The coefficient of performance (COP) of a heat pump is defined as: A) Heating output ÷ Electrical input B) Cooling output ÷ Refrigerant mass flow C) Total BTU output ÷ Fuel consumption D) Fan power ÷ Total system power Correct Answer: A) Heating output ÷ Electrical input Explanation: COP = heating (or cooling) output divided by the electrical energy consumed. Higher COP indicates greater efficiency. Question 48: During the defrost cycle of an air-source heat pump: A) The reversing valve switches to cooling mode while the outdoor fan stops B) The reversing valve switches to heating mode while the indoor fan runs C) The outdoor coil operates as an evaporator to melt frost D) The indoor coil is shut off and the system runs on auxiliary electric heat Correct Answer: C) The outdoor coil operates as an evaporator to melt frost Explanation: In defrost, the outdoor coil becomes the evaporator, drawing heat from the indoor air to melt accumulated frost. Question 49: Which type of heat pump system uses the earth as a heat source and heat sink?
A) Air-source heat pump B) Water-source heat pump C) Geothermal heat pump D) Absorption heat pump Correct Answer: C) Geothermal heat pump Explanation: Geothermal (ground-source) heat pumps use the relatively constant temperature of the earth to provide heating and cooling, offering high efficiency.
SECTION 8: SYSTEM TYPES
Question 50: Variable Refrigerant Flow (VRF) systems are particularly beneficial for: A) Single-room window units B) Large buildings requiring individualized zone temperature control C) Buildings that do not require zoning D) Areas with consistent humidity only Correct Answer: B) Large buildings requiring individualized zone temperature control Explanation: VRF systems allow for customized temperature control in different zones or rooms within large commercial or residential buildings by modulating the flow of refrigerant to multiple indoor units. Question 51: A ductless mini-split system is often the preferred choice for: A) Large shopping malls B) Older homes or additions where installing ductwork is cost-prohibitive C) New construction with pre-planned ductwork D) High-rise office buildings Correct Answer: B) Older homes or additions where installing ductwork is cost- prohibitive
