MASTER MECHANICAL-G29-N CONTRACTOR EXAM – QUESTIONS AND
ANSWERS | VERIFIED AND WELL DETAILED ANSWERS | PLUS RATIONALES |
DOWNLOAD AND PASS | LATEST EXAM UPDATE 2026/2027
Core Domains
Heating, Ventilation, and Air Conditioning (HVAC) Systems
Refrigeration Cycle and Principles
Electrical Theory and Application
Gas Piping, Combustion, and Venting
Hydronic Heating and Cooling Systems
Building Codes, Standards, and Safety Regulations
System Controls, Instrumentation, and Diagnostics
Load Calculation and Energy Efficiency
Air Distribution and Duct Design
Professional Ethics and Business Practices
Introduction
This comprehensive examination is designed to rigorously assess the knowledge,
skills, and professional judgment required for successful practice as a Mechanical-
G29-N Contractor. The content spans foundational scientific theory, practical
application of trade principles, and critical decision-making in complex, real-world
scenarios. Candidates are evaluated on their understanding of HVAC and
refrigeration systems, electrical components, gas and hydronic system design, and
adherence to applicable codes and safety standards. The examination employs a
mix of direct knowledge questions and problem-based scenarios to gauge the
contractor's readiness to operate safely, efficiently, and ethically in the field,
ensuring protection of life, property, and the environment.
,SECTION ONE: QUESTIONS 1–50
1. A technician is inspecting a gas-fired furnace and finds that the main burner
flame is lifting off the burner ports. What is the most likely cause of this
condition?
A. Insufficient primary air
B. Low manifold gas pressure
C. High primary air flow
D. A dirty air filter
🟢 Correct Answer: C. High primary air flow
🔴 Explanation: Flame lifting occurs when the air-gas mixture velocity exceeds
the flame propagation speed. Excessive primary air causes the flame to lift off the
burner ports. Insufficient primary air would result in a yellow, sooty flame, not
lifting.
2. In a vapor-compression refrigeration cycle, where does the refrigerant exist as a
high-pressure, high-temperature superheated vapor?
A. At the evaporator inlet
B. At the compressor discharge
C. At the condenser outlet
D. At the expansion valve inlet
🟢 Correct Answer: B. At the compressor discharge
🔴 Explanation: The compressor draws in low-pressure superheated vapor from
the evaporator and compresses it, significantly raising its pressure and
temperature. The discharge line carries this high-pressure, high-temperature
superheated vapor to the condenser.
,3. What is the maximum allowable pressure drop for a natural gas piping system
from the meter to the appliance, as typically specified in the National Fuel Gas
Code (NFPA 54)?
A. 0.5 inches of water column
B. 1.0 inches of water column
C. 1.5 inches of water column
D. 2.5 inches of water column
🟢 Correct Answer: A. 0.5 inches of water column
🔴 Explanation: The National Fuel Gas Code (NFPA 54) generally recommends a
maximum pressure drop of 0.5 inches of water column (125 Pa) for low-pressure
gas systems. This ensures that the appliance receives adequate pressure for
proper operation and capacity.
4. A condensing gas furnace has an Annual Fuel Utilization Efficiency (AFUE)
rating of 95%. This rating indicates that:
A. The furnace converts 95% of its energy input into usable work.
B. The furnace is 95% efficient at converting fuel to electricity.
C. The furnace has an input of 95,000 Btu/h and an output of 100,000 Btu/h.
D. The furnace emits 95% less pollution than a standard model.
🟢 Correct Answer: A. The furnace converts 95% of its energy input into usable
work.
🔴 Explanation: AFUE is a measure of thermal efficiency. It represents the ratio of
the furnace's annual heat output to the annual energy input, expressed as a
percentage. A 95% AFUE means that 95% of the fuel's energy is converted into
useful heat.
5. What type of electrical motor protection device is designed to interrupt the
circuit if the motor draws excessive current due to a locked rotor or overload
, condition, and automatically resets after a cooling period?
A. Thermal overload relay
B. Fuse
C. Circuit breaker
D. Magnetic starter
🟢 Correct Answer: A. Thermal overload relay
🔴 Explanation: A thermal overload relay uses a bimetallic strip or a heater
element that heats up in response to excessive current. Once heated, the bimetal
bends and opens the control circuit, shutting off the motor. It is an automatic
reset device, resetting once the element has cooled.
6. When charging a system with a blended refrigerant, such as R-410A, what is
the correct charging method to maintain the proper refrigerant composition?
A. Liquid charging into the low side
B. Vapor charging into the low side
C. Liquid charging into the high side
D. Charging as a vapor after passing through a desiccant
🟢 Correct Answer: C. Liquid charging into the high side
🔴 Explanation: Refrigerant blends have components with different boiling
points. If charged as a vapor, the blend can fractionate, changing the mixture's
composition. Liquid charging, usually into the high side, ensures the entire blend
enters the system as a liquid, maintaining the correct proportions.
7. A project calls for the installation of a 5-ton air conditioning unit. What is the
approximate cooling capacity of this unit in BTUs per hour?
A. 12,000 Btu/h
B. 24,000 Btu/h
ANSWERS | VERIFIED AND WELL DETAILED ANSWERS | PLUS RATIONALES |
DOWNLOAD AND PASS | LATEST EXAM UPDATE 2026/2027
Core Domains
Heating, Ventilation, and Air Conditioning (HVAC) Systems
Refrigeration Cycle and Principles
Electrical Theory and Application
Gas Piping, Combustion, and Venting
Hydronic Heating and Cooling Systems
Building Codes, Standards, and Safety Regulations
System Controls, Instrumentation, and Diagnostics
Load Calculation and Energy Efficiency
Air Distribution and Duct Design
Professional Ethics and Business Practices
Introduction
This comprehensive examination is designed to rigorously assess the knowledge,
skills, and professional judgment required for successful practice as a Mechanical-
G29-N Contractor. The content spans foundational scientific theory, practical
application of trade principles, and critical decision-making in complex, real-world
scenarios. Candidates are evaluated on their understanding of HVAC and
refrigeration systems, electrical components, gas and hydronic system design, and
adherence to applicable codes and safety standards. The examination employs a
mix of direct knowledge questions and problem-based scenarios to gauge the
contractor's readiness to operate safely, efficiently, and ethically in the field,
ensuring protection of life, property, and the environment.
,SECTION ONE: QUESTIONS 1–50
1. A technician is inspecting a gas-fired furnace and finds that the main burner
flame is lifting off the burner ports. What is the most likely cause of this
condition?
A. Insufficient primary air
B. Low manifold gas pressure
C. High primary air flow
D. A dirty air filter
🟢 Correct Answer: C. High primary air flow
🔴 Explanation: Flame lifting occurs when the air-gas mixture velocity exceeds
the flame propagation speed. Excessive primary air causes the flame to lift off the
burner ports. Insufficient primary air would result in a yellow, sooty flame, not
lifting.
2. In a vapor-compression refrigeration cycle, where does the refrigerant exist as a
high-pressure, high-temperature superheated vapor?
A. At the evaporator inlet
B. At the compressor discharge
C. At the condenser outlet
D. At the expansion valve inlet
🟢 Correct Answer: B. At the compressor discharge
🔴 Explanation: The compressor draws in low-pressure superheated vapor from
the evaporator and compresses it, significantly raising its pressure and
temperature. The discharge line carries this high-pressure, high-temperature
superheated vapor to the condenser.
,3. What is the maximum allowable pressure drop for a natural gas piping system
from the meter to the appliance, as typically specified in the National Fuel Gas
Code (NFPA 54)?
A. 0.5 inches of water column
B. 1.0 inches of water column
C. 1.5 inches of water column
D. 2.5 inches of water column
🟢 Correct Answer: A. 0.5 inches of water column
🔴 Explanation: The National Fuel Gas Code (NFPA 54) generally recommends a
maximum pressure drop of 0.5 inches of water column (125 Pa) for low-pressure
gas systems. This ensures that the appliance receives adequate pressure for
proper operation and capacity.
4. A condensing gas furnace has an Annual Fuel Utilization Efficiency (AFUE)
rating of 95%. This rating indicates that:
A. The furnace converts 95% of its energy input into usable work.
B. The furnace is 95% efficient at converting fuel to electricity.
C. The furnace has an input of 95,000 Btu/h and an output of 100,000 Btu/h.
D. The furnace emits 95% less pollution than a standard model.
🟢 Correct Answer: A. The furnace converts 95% of its energy input into usable
work.
🔴 Explanation: AFUE is a measure of thermal efficiency. It represents the ratio of
the furnace's annual heat output to the annual energy input, expressed as a
percentage. A 95% AFUE means that 95% of the fuel's energy is converted into
useful heat.
5. What type of electrical motor protection device is designed to interrupt the
circuit if the motor draws excessive current due to a locked rotor or overload
, condition, and automatically resets after a cooling period?
A. Thermal overload relay
B. Fuse
C. Circuit breaker
D. Magnetic starter
🟢 Correct Answer: A. Thermal overload relay
🔴 Explanation: A thermal overload relay uses a bimetallic strip or a heater
element that heats up in response to excessive current. Once heated, the bimetal
bends and opens the control circuit, shutting off the motor. It is an automatic
reset device, resetting once the element has cooled.
6. When charging a system with a blended refrigerant, such as R-410A, what is
the correct charging method to maintain the proper refrigerant composition?
A. Liquid charging into the low side
B. Vapor charging into the low side
C. Liquid charging into the high side
D. Charging as a vapor after passing through a desiccant
🟢 Correct Answer: C. Liquid charging into the high side
🔴 Explanation: Refrigerant blends have components with different boiling
points. If charged as a vapor, the blend can fractionate, changing the mixture's
composition. Liquid charging, usually into the high side, ensures the entire blend
enters the system as a liquid, maintaining the correct proportions.
7. A project calls for the installation of a 5-ton air conditioning unit. What is the
approximate cooling capacity of this unit in BTUs per hour?
A. 12,000 Btu/h
B. 24,000 Btu/h
