640-LA SecondClass Stationary
Air Conditioning Contractor Exam
latest updated test with must
know questions 2026
1. Which of the following best describes the primary function of a compressor in a vapor-
compression refrigeration cycle?
a) To absorb heat from the conditioned space
b) To reject heat to the outside air
c) To increase the pressure and temperature of the refrigerant vapor
d) To expand the refrigerant from a high-pressure liquid to a low-pressure liquid/vapor mix
Correct Answer: c) To increase the pressure and temperature of the refrigerant vapor
Rationale: The compressor is the heart of the refrigeration cycle. It draws in low-pressure,
low-temperature refrigerant vapor and compresses it, significantly increasing both its
pressure and temperature. This prepares the refrigerant to release heat in the condenser.
2. The term "latent heat" in an air conditioning context refers to:
a) Heat that directly raises the temperature of a substance
b) Heat required to induce a phase change without a temperature change
c) Additional heat from solar radiation
d) Heat lost through uninsulated ducts
Correct Answer: b) Heat required to induce a phase change without a temperature
change
Rationale: Latent heat is the energy absorbed or released during a change of state (e.g.,
from liquid to gas or gas to liquid) without a change in temperature. In air conditioning, this
is most commonly associated with the removal of moisture (condensation) from the air.
3. What is the recommended maximum velocity for air in a low-pressure commercial
supply duct to minimize noise?
a) 500 feet per minute (fpm)
b) 1,200 feet per minute (fpm)
c) 2,500 feet per minute (fpm)
d) 4,000 feet per minute (fpm)
Correct Answer: b) 1,200 feet per minute (fpm)
,Rationale: To prevent excessive noise and pressure drop, standard industry practice for low-
pressure duct systems recommends maintaining air velocities in main supply ducts below
approximately 1,200 to 1,500 fpm.
4. Which of the following refrigerants has the lowest Global Warming Potential (GWP)
among the options and is considered a lower-GWP alternative in new equipment?
a) R-410A
b) R-134a
c) R-22
d) R-32
Correct Answer: d) R-32
Rationale: While R-32 is a hydrofluorocarbon (HFC) and classified as A2L (mildly flammable),
its GWP is approximately one-third that of R-410A. It is becoming a common lower-GWP
alternative in new air conditioning equipment.
5. In the refrigeration cycle, what is the main purpose of a condenser?
a) To absorb heat from the supply air passing over it.
b) To transfer heat from the refrigerant to the outside air, causing the refrigerant to
condense.
c) To humidify the supply air stream.
d) To filter particulate matter from the return air.
Correct Answer: b) To transfer heat from the refrigerant to the outside air, causing
the refrigerant to condense.
Rationale: The condenser receives high-pressure, high-temperature refrigerant vapor from
the compressor. Its job is to reject that heat to a cooler medium (usually outside air), causing
the refrigerant to condense into a high-pressure liquid.
6. A thermostatic expansion valve (TXV) controls refrigerant flow into the evaporator
based on:
a) Evaporator pressure.
b) Condenser pressure.
c) Superheat at the evaporator outlet.
d) Subcooling at the condenser outlet.
Correct Answer: c) Superheat at the evaporator outlet.
Rationale: A TXV senses the temperature and pressure at the evaporator outlet to maintain
a constant superheat. This ensures that the evaporator is being fed the correct amount of
refrigerant to maximize efficiency while preventing liquid refrigerant from returning to the
compressor (floodback).
, 7. When performing a pump-down on a refrigeration system for service, which component
is used to trap and store the refrigerant?
a) The oil separator.
b) The liquid line receiver or the condenser.
c) The accumulator.
d) The evaporator.
Correct Answer: b) The liquid line receiver or the condenser.
Rationale: A pump-down procedure uses the compressor to move the entire system's
refrigerant charge into the receiver and condenser. The liquid line solenoid valve closes,
trapping the refrigerant there so the rest of the system can be safely opened for service.
8. What is the primary risk of pulling an excessively deep vacuum (e.g., below 200
microns) too quickly during system evacuation?
a) It can cause the compressor oil to break down.
b) It can freeze residual moisture in the system, slowing the dehydration process.
c) It provides no additional benefit and wastes time.
d) It will always indicate a significant leak.
Correct Answer: b) It can freeze residual moisture in the system, slowing the
dehydration process.
Rationale: If a vacuum is pulled below the vapor pressure of water at the ambient
temperature (e.g., 4,500 microns at 32°F), any remaining moisture can freeze into ice. This
ice then must sublimate (turn from solid to vapor), which is a much slower process,
hampering the evacuation.
9. Which of the following is a key purpose of a balancing valve in a hydronic system?
a) To prevent water from flowing backwards.
b) To manually set and measure flow rate in a specific branch or circuit.
c) To automatically maintain a constant differential pressure.
d) To act as the main system shutoff.
Correct Answer: b) To manually set and measure flow rate in a specific branch or
circuit.
Rationale: Balancing valves, often used in conjunction with pressure/temperature ports,
allow a technician to precisely set and verify the correct water flow rate (GPM) to each zone
or air handling unit, ensuring the system delivers the proper heating or cooling.
10. According to the Louisiana State Licensing Board for Contractors (LSLBC), an HVAC
contractor's license is generally required for commercial projects where the contract value
exceeds what amount?
a) $5,000
Air Conditioning Contractor Exam
latest updated test with must
know questions 2026
1. Which of the following best describes the primary function of a compressor in a vapor-
compression refrigeration cycle?
a) To absorb heat from the conditioned space
b) To reject heat to the outside air
c) To increase the pressure and temperature of the refrigerant vapor
d) To expand the refrigerant from a high-pressure liquid to a low-pressure liquid/vapor mix
Correct Answer: c) To increase the pressure and temperature of the refrigerant vapor
Rationale: The compressor is the heart of the refrigeration cycle. It draws in low-pressure,
low-temperature refrigerant vapor and compresses it, significantly increasing both its
pressure and temperature. This prepares the refrigerant to release heat in the condenser.
2. The term "latent heat" in an air conditioning context refers to:
a) Heat that directly raises the temperature of a substance
b) Heat required to induce a phase change without a temperature change
c) Additional heat from solar radiation
d) Heat lost through uninsulated ducts
Correct Answer: b) Heat required to induce a phase change without a temperature
change
Rationale: Latent heat is the energy absorbed or released during a change of state (e.g.,
from liquid to gas or gas to liquid) without a change in temperature. In air conditioning, this
is most commonly associated with the removal of moisture (condensation) from the air.
3. What is the recommended maximum velocity for air in a low-pressure commercial
supply duct to minimize noise?
a) 500 feet per minute (fpm)
b) 1,200 feet per minute (fpm)
c) 2,500 feet per minute (fpm)
d) 4,000 feet per minute (fpm)
Correct Answer: b) 1,200 feet per minute (fpm)
,Rationale: To prevent excessive noise and pressure drop, standard industry practice for low-
pressure duct systems recommends maintaining air velocities in main supply ducts below
approximately 1,200 to 1,500 fpm.
4. Which of the following refrigerants has the lowest Global Warming Potential (GWP)
among the options and is considered a lower-GWP alternative in new equipment?
a) R-410A
b) R-134a
c) R-22
d) R-32
Correct Answer: d) R-32
Rationale: While R-32 is a hydrofluorocarbon (HFC) and classified as A2L (mildly flammable),
its GWP is approximately one-third that of R-410A. It is becoming a common lower-GWP
alternative in new air conditioning equipment.
5. In the refrigeration cycle, what is the main purpose of a condenser?
a) To absorb heat from the supply air passing over it.
b) To transfer heat from the refrigerant to the outside air, causing the refrigerant to
condense.
c) To humidify the supply air stream.
d) To filter particulate matter from the return air.
Correct Answer: b) To transfer heat from the refrigerant to the outside air, causing
the refrigerant to condense.
Rationale: The condenser receives high-pressure, high-temperature refrigerant vapor from
the compressor. Its job is to reject that heat to a cooler medium (usually outside air), causing
the refrigerant to condense into a high-pressure liquid.
6. A thermostatic expansion valve (TXV) controls refrigerant flow into the evaporator
based on:
a) Evaporator pressure.
b) Condenser pressure.
c) Superheat at the evaporator outlet.
d) Subcooling at the condenser outlet.
Correct Answer: c) Superheat at the evaporator outlet.
Rationale: A TXV senses the temperature and pressure at the evaporator outlet to maintain
a constant superheat. This ensures that the evaporator is being fed the correct amount of
refrigerant to maximize efficiency while preventing liquid refrigerant from returning to the
compressor (floodback).
, 7. When performing a pump-down on a refrigeration system for service, which component
is used to trap and store the refrigerant?
a) The oil separator.
b) The liquid line receiver or the condenser.
c) The accumulator.
d) The evaporator.
Correct Answer: b) The liquid line receiver or the condenser.
Rationale: A pump-down procedure uses the compressor to move the entire system's
refrigerant charge into the receiver and condenser. The liquid line solenoid valve closes,
trapping the refrigerant there so the rest of the system can be safely opened for service.
8. What is the primary risk of pulling an excessively deep vacuum (e.g., below 200
microns) too quickly during system evacuation?
a) It can cause the compressor oil to break down.
b) It can freeze residual moisture in the system, slowing the dehydration process.
c) It provides no additional benefit and wastes time.
d) It will always indicate a significant leak.
Correct Answer: b) It can freeze residual moisture in the system, slowing the
dehydration process.
Rationale: If a vacuum is pulled below the vapor pressure of water at the ambient
temperature (e.g., 4,500 microns at 32°F), any remaining moisture can freeze into ice. This
ice then must sublimate (turn from solid to vapor), which is a much slower process,
hampering the evacuation.
9. Which of the following is a key purpose of a balancing valve in a hydronic system?
a) To prevent water from flowing backwards.
b) To manually set and measure flow rate in a specific branch or circuit.
c) To automatically maintain a constant differential pressure.
d) To act as the main system shutoff.
Correct Answer: b) To manually set and measure flow rate in a specific branch or
circuit.
Rationale: Balancing valves, often used in conjunction with pressure/temperature ports,
allow a technician to precisely set and verify the correct water flow rate (GPM) to each zone
or air handling unit, ensuring the system delivers the proper heating or cooling.
10. According to the Louisiana State Licensing Board for Contractors (LSLBC), an HVAC
contractor's license is generally required for commercial projects where the contract value
exceeds what amount?
a) $5,000
