Louisiana (New Orleans) Second Class Stationary
Air Conditioning - 640-LA Contractor Exam |
Verified Latest Questions and Correct Detailed
Answers
OVERVIEW DESCRIPTION:
The 640-LA Second Class Stationary Air Conditioning exam is a critical licensing step for
commercial HVAC contractors in Louisiana, mandated by the LSLBC for projects valued at
$10,000 or more. Administered as an open-book test through PSI with a four-hour time limit, it
requires a 70% passing score. The exam thoroughly assesses a candidate's competency across
the full spectrum of the trade, including HVAC and refrigeration systems, air distribution,
piping, electrical controls, refrigerant handling, maintenance procedures, and project
management fundamentals. Its comprehensive scope ensures that licensed contractors possess
the necessary technical knowledge and practical judgment to design, install, and service complex
commercial stationary air conditioning systems safely and in accordance with industry
standards.
QUESTION 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
EXPERT RATIONALE:
The compressor's function is to pump refrigerant by taking in low-pressure, low-
temperature vapor and discharging it as high-pressure, high-temperature vapor to
begin the heat rejection process.
,QUESTION 2
What is the term for the temperature at which moisture in the air begins to condense on
a surface?
A. Wet-bulb temperature
B. Sensible temperature
C. Dry-bulb temperature
D. Dew point temperature
CORRECT ANSWER ✓ ✓
D. Dew point temperature
EXPERT RATIONALE:
The dew point is the temperature at which the air becomes fully saturated and water
vapor begins to condense, a critical concept for humidity control and coil operation.
QUESTION 3
Which type of compressor uses a rotating motion to draw in and compress refrigerant,
is known for quiet operation, and is commonly used in residential systems?
A. Centrifugal Compressor
B. Screw Compressor
C. Scroll Compressor
D. Reciprocating Compressor
CORRECT ANSWER ✓ ✓
C. Scroll Compressor
EXPERT RATIONALE:
Scroll compressors use two intermeshing spiral scrolls to compress refrigerant, offering
quiet, reliable, and efficient operation, making them prevalent in modern residential and
light commercial systems.
QUESTION 4
For a commercial project in New Orleans with a contract value of $12,000, which
,Louisiana contractor license is legally required for the HVAC work?
A. No state license is required for work under $50,000.
B. Residential Building Contractor License.
C. Second Class Stationary Air Conditioning (640-LA) License.
D. A city occupational license only.
CORRECT ANSWER ✓ ✓
C. Second Class Stationary Air Conditioning (640-LA) License.
EXPERT RATIONALE:
Louisiana law requires a Second Class Stationary Air Conditioning license for commercial
HVAC projects with a contract price of $10,000 or more, and $12,000 exceeds this
threshold.
QUESTION 5
When brazing a refrigerant line, what is the primary purpose of using an inert purge gas,
such as nitrogen?
A. To increase the flame temperature for a stronger joint.
B. To prevent the formation of copper oxide scale inside the pipe.
C. To help visually inspect the joint for leaks.
D. To lubricate the fitting for easier assembly.
CORRECT ANSWER ✓ ✓
B. To prevent the formation of copper oxide scale inside the pipe.
EXPERT RATIONALE:
Flowing nitrogen during brazing displaces oxygen, preventing oxidation and the
formation of harmful scale inside the piping that can contaminate the system and
damage components.
QUESTION 6
In a direct expansion (DX) air handling unit, what is the primary function of the
evaporator coil?
, A. To reject heat from the refrigerant to the outside air.
B. To absorb heat from the supply air passing over it.
C. To humidify the supply air stream.
D. To filter particulate matter from the return air.
CORRECT ANSWER ✓ ✓
B. To absorb heat from the supply air passing over it.
EXPERT RATIONALE:
In the evaporator, cold, low-pressure refrigerant absorbs sensible and latent heat from
the warmer air blown across the coil, cooling and dehumidifying the air.
QUESTION 7
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)
EXPERT RATIONALE:
For low-pressure duct systems, maintaining air velocity below approximately 1,200 to
1,500 fpm in main ducts is standard practice to avoid excessive noise and pressure drop.
QUESTION 8
Which of the following refrigerants has the lowest Global Warming Potential (GWP) and
is considered an A1 (lower toxicity, no flame propagation) safety classification?
A. R-410A
B. R-134a
Air Conditioning - 640-LA Contractor Exam |
Verified Latest Questions and Correct Detailed
Answers
OVERVIEW DESCRIPTION:
The 640-LA Second Class Stationary Air Conditioning exam is a critical licensing step for
commercial HVAC contractors in Louisiana, mandated by the LSLBC for projects valued at
$10,000 or more. Administered as an open-book test through PSI with a four-hour time limit, it
requires a 70% passing score. The exam thoroughly assesses a candidate's competency across
the full spectrum of the trade, including HVAC and refrigeration systems, air distribution,
piping, electrical controls, refrigerant handling, maintenance procedures, and project
management fundamentals. Its comprehensive scope ensures that licensed contractors possess
the necessary technical knowledge and practical judgment to design, install, and service complex
commercial stationary air conditioning systems safely and in accordance with industry
standards.
QUESTION 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
EXPERT RATIONALE:
The compressor's function is to pump refrigerant by taking in low-pressure, low-
temperature vapor and discharging it as high-pressure, high-temperature vapor to
begin the heat rejection process.
,QUESTION 2
What is the term for the temperature at which moisture in the air begins to condense on
a surface?
A. Wet-bulb temperature
B. Sensible temperature
C. Dry-bulb temperature
D. Dew point temperature
CORRECT ANSWER ✓ ✓
D. Dew point temperature
EXPERT RATIONALE:
The dew point is the temperature at which the air becomes fully saturated and water
vapor begins to condense, a critical concept for humidity control and coil operation.
QUESTION 3
Which type of compressor uses a rotating motion to draw in and compress refrigerant,
is known for quiet operation, and is commonly used in residential systems?
A. Centrifugal Compressor
B. Screw Compressor
C. Scroll Compressor
D. Reciprocating Compressor
CORRECT ANSWER ✓ ✓
C. Scroll Compressor
EXPERT RATIONALE:
Scroll compressors use two intermeshing spiral scrolls to compress refrigerant, offering
quiet, reliable, and efficient operation, making them prevalent in modern residential and
light commercial systems.
QUESTION 4
For a commercial project in New Orleans with a contract value of $12,000, which
,Louisiana contractor license is legally required for the HVAC work?
A. No state license is required for work under $50,000.
B. Residential Building Contractor License.
C. Second Class Stationary Air Conditioning (640-LA) License.
D. A city occupational license only.
CORRECT ANSWER ✓ ✓
C. Second Class Stationary Air Conditioning (640-LA) License.
EXPERT RATIONALE:
Louisiana law requires a Second Class Stationary Air Conditioning license for commercial
HVAC projects with a contract price of $10,000 or more, and $12,000 exceeds this
threshold.
QUESTION 5
When brazing a refrigerant line, what is the primary purpose of using an inert purge gas,
such as nitrogen?
A. To increase the flame temperature for a stronger joint.
B. To prevent the formation of copper oxide scale inside the pipe.
C. To help visually inspect the joint for leaks.
D. To lubricate the fitting for easier assembly.
CORRECT ANSWER ✓ ✓
B. To prevent the formation of copper oxide scale inside the pipe.
EXPERT RATIONALE:
Flowing nitrogen during brazing displaces oxygen, preventing oxidation and the
formation of harmful scale inside the piping that can contaminate the system and
damage components.
QUESTION 6
In a direct expansion (DX) air handling unit, what is the primary function of the
evaporator coil?
, A. To reject heat from the refrigerant to the outside air.
B. To absorb heat from the supply air passing over it.
C. To humidify the supply air stream.
D. To filter particulate matter from the return air.
CORRECT ANSWER ✓ ✓
B. To absorb heat from the supply air passing over it.
EXPERT RATIONALE:
In the evaporator, cold, low-pressure refrigerant absorbs sensible and latent heat from
the warmer air blown across the coil, cooling and dehumidifying the air.
QUESTION 7
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)
EXPERT RATIONALE:
For low-pressure duct systems, maintaining air velocity below approximately 1,200 to
1,500 fpm in main ducts is standard practice to avoid excessive noise and pressure drop.
QUESTION 8
Which of the following refrigerants has the lowest Global Warming Potential (GWP) and
is considered an A1 (lower toxicity, no flame propagation) safety classification?
A. R-410A
B. R-134a
