LOUISIANA (NEW ORLEANS) SECOND CLASS STATIONARY AIR CONDITIONING - 640-LA
CONTRACTOR EXAM PRACTICE TEST EXAM QUESTIONS AND CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES 2026 Q&A |LATEST EXAM UPDATE 2026/2027..
Core Domains
Thermodynamic Principles and Refrigeration Cycles
Compressor Types, Operation, and Maintenance
Condensers, Evaporators, and Cooling Towers
Pumps, Piping, and Water Treatment Systems
Air Handling Systems, Ventilation, and Ductwork
Pneumatic and Electronic Control Systems
Electrical Circuits, Motors, and Safety Controls
City of New Orleans Mechanical Codes and Safety Regulations
Introduction
This examination serves to evaluate the competency, technical proficiency, and safety awareness of
candidates seeking licensure as a Second Class Stationary Air Conditioning Contractor in New Orleans.
The assessment measures essential knowledge regarding the installation, operation, troubleshooting,
and maintenance of commercial and industrial refrigeration and air conditioning systems. Candidates are
tested on both theoretical foundations and practical applications, including fluid mechanics, electrical
troubleshooting, and compliance with local municipal codes. Utilizing a blend of direct knowledge
questions and complex field scenarios, the exam emphasizes critical thinking, operational efficiency, and
the protection of public safety through rigorous adherence to industry standards.
What is the primary function of an expansion valve in a standard vapor-compression refrigeration
cycle?
,A. To increase refrigerant pressure and temperature before the condenser
B. To reduce refrigerant pressure and temperature before the evaporator
C. To absorb latent heat from the compressor motor winding
D. To regulate superheat exiting the liquid receiver
🟢 B. To reduce refrigerant pressure and temperature before the evaporator
🔴 RATIONALE: The expansion valve creates a pressure drop, causing a portion of the liquid
refrigerant to flash into a low-temperature, low-pressure mixture capable of absorbing heat in the
evaporator.
In a centrifugal chiller system, low oil pressure safety controls typically initiate a shutdown to
prevent damage to which main component?
A. Purge unit
B. Cooling tower fan
C. Compressor bearings
D. Expansion valve
🟢 C. Compressor bearings
🔴 RATIONALE: Centrifugal compressors rely on continuous positive oil pressure to lubricate high-
speed rotating bearings. A loss of pressure results in catastrophic bearing failure.
Which psychrometric property represents the total heat content of air, including both sensible and
latent heat?
A. Relative humidity
B. Dew point temperature
C. Wet-bulb temperature
D. Enthalpy
🟢 D. Enthalpy
,🔴 RATIONALE: Enthalpy measures the total thermal energy in a mass of air, accounting for both
dry-bulb temperature (sensible) and moisture content (latent).
According to standard mechanical safety practices, what is the minimum required clearance in front
of electrical control panels for large chiller units?
A. 24 inches
B. 36 inches
C. 42 inches
D. 48 inches
🟢 B. 36 inches
🔴 RATIONALE: National electrical safety standards mandate a minimum workspace clearance of
36 inches in front of electrical equipment operating at typical commercial voltage levels to ensure
safe technician access.
When performing a leak check on a low-pressure centrifugal chiller using CFC or HCFC
refrigerants, what method is preferred while the system is idle and pressurized with nitrogen?
A. Halide torch testing
B. Electronic leak detection and soap bubble testing
C. Submerging the entire chiller vessel in water
D. Monitoring compressor oil color changes
🟢 B. Electronic leak detection and soap bubble testing
🔴 RATIONALE: Pressurizing a low-pressure vessel with dry nitrogen allows the safe and effective
use of electronic leak detectors and bubble solutions to pinpoint micro-leaks.
What is the primary cause of water scaling in an open-loop cooling tower condenser circuit?
A. Low system operating pressures
B. Excessive accumulation of dissolved minerals due to evaporation
C. Bacterial growth from inadequate biocide treatment
, D. Improper compressor oil mixing with cooling water
🟢 B. Excessive accumulation of dissolved minerals due to evaporation
🔴 RATIONALE: As pure water evaporates from a cooling tower, dissolved calcium and
magnesium minerals concentrate in the remaining water, eventually precipitating out as scale on
heat transfer surfaces.
In a pneumatic control system, what is the standard branch line pressure range used to modulate a
pneumatic actuator?
A. 0 to 5 psig
B. 3 to 15 psig
C. 0 to 100 psig
D. 20 to 50 psig
🟢 B. 3 to 15 psig
🔴 RATIONALE: Standard commercial pneumatic control loops utilize a 3 psig to 15 psig signal
range to position valves and dampers proportionally.
A reciprocating compressor exhibits short-cycling. Which of the following is the most probable
electrical or control root cause?
A. Defective low-pressure cutout or thermostat differential set too narrow
B. Oversized condenser water pump motor
C. Excessive refrigerant subcooling
D. High oil return velocity in the suction line
🟢 A. Defective low-pressure cutout or thermostat differential set too narrow
🔴 RATIONALE: A narrow differential or a failing pressure switch causes the compressor to satisfy
load requirements and shut down too quickly, leading to rapid restarts and equipment wear.
CONTRACTOR EXAM PRACTICE TEST EXAM QUESTIONS AND CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES 2026 Q&A |LATEST EXAM UPDATE 2026/2027..
Core Domains
Thermodynamic Principles and Refrigeration Cycles
Compressor Types, Operation, and Maintenance
Condensers, Evaporators, and Cooling Towers
Pumps, Piping, and Water Treatment Systems
Air Handling Systems, Ventilation, and Ductwork
Pneumatic and Electronic Control Systems
Electrical Circuits, Motors, and Safety Controls
City of New Orleans Mechanical Codes and Safety Regulations
Introduction
This examination serves to evaluate the competency, technical proficiency, and safety awareness of
candidates seeking licensure as a Second Class Stationary Air Conditioning Contractor in New Orleans.
The assessment measures essential knowledge regarding the installation, operation, troubleshooting,
and maintenance of commercial and industrial refrigeration and air conditioning systems. Candidates are
tested on both theoretical foundations and practical applications, including fluid mechanics, electrical
troubleshooting, and compliance with local municipal codes. Utilizing a blend of direct knowledge
questions and complex field scenarios, the exam emphasizes critical thinking, operational efficiency, and
the protection of public safety through rigorous adherence to industry standards.
What is the primary function of an expansion valve in a standard vapor-compression refrigeration
cycle?
,A. To increase refrigerant pressure and temperature before the condenser
B. To reduce refrigerant pressure and temperature before the evaporator
C. To absorb latent heat from the compressor motor winding
D. To regulate superheat exiting the liquid receiver
🟢 B. To reduce refrigerant pressure and temperature before the evaporator
🔴 RATIONALE: The expansion valve creates a pressure drop, causing a portion of the liquid
refrigerant to flash into a low-temperature, low-pressure mixture capable of absorbing heat in the
evaporator.
In a centrifugal chiller system, low oil pressure safety controls typically initiate a shutdown to
prevent damage to which main component?
A. Purge unit
B. Cooling tower fan
C. Compressor bearings
D. Expansion valve
🟢 C. Compressor bearings
🔴 RATIONALE: Centrifugal compressors rely on continuous positive oil pressure to lubricate high-
speed rotating bearings. A loss of pressure results in catastrophic bearing failure.
Which psychrometric property represents the total heat content of air, including both sensible and
latent heat?
A. Relative humidity
B. Dew point temperature
C. Wet-bulb temperature
D. Enthalpy
🟢 D. Enthalpy
,🔴 RATIONALE: Enthalpy measures the total thermal energy in a mass of air, accounting for both
dry-bulb temperature (sensible) and moisture content (latent).
According to standard mechanical safety practices, what is the minimum required clearance in front
of electrical control panels for large chiller units?
A. 24 inches
B. 36 inches
C. 42 inches
D. 48 inches
🟢 B. 36 inches
🔴 RATIONALE: National electrical safety standards mandate a minimum workspace clearance of
36 inches in front of electrical equipment operating at typical commercial voltage levels to ensure
safe technician access.
When performing a leak check on a low-pressure centrifugal chiller using CFC or HCFC
refrigerants, what method is preferred while the system is idle and pressurized with nitrogen?
A. Halide torch testing
B. Electronic leak detection and soap bubble testing
C. Submerging the entire chiller vessel in water
D. Monitoring compressor oil color changes
🟢 B. Electronic leak detection and soap bubble testing
🔴 RATIONALE: Pressurizing a low-pressure vessel with dry nitrogen allows the safe and effective
use of electronic leak detectors and bubble solutions to pinpoint micro-leaks.
What is the primary cause of water scaling in an open-loop cooling tower condenser circuit?
A. Low system operating pressures
B. Excessive accumulation of dissolved minerals due to evaporation
C. Bacterial growth from inadequate biocide treatment
, D. Improper compressor oil mixing with cooling water
🟢 B. Excessive accumulation of dissolved minerals due to evaporation
🔴 RATIONALE: As pure water evaporates from a cooling tower, dissolved calcium and
magnesium minerals concentrate in the remaining water, eventually precipitating out as scale on
heat transfer surfaces.
In a pneumatic control system, what is the standard branch line pressure range used to modulate a
pneumatic actuator?
A. 0 to 5 psig
B. 3 to 15 psig
C. 0 to 100 psig
D. 20 to 50 psig
🟢 B. 3 to 15 psig
🔴 RATIONALE: Standard commercial pneumatic control loops utilize a 3 psig to 15 psig signal
range to position valves and dampers proportionally.
A reciprocating compressor exhibits short-cycling. Which of the following is the most probable
electrical or control root cause?
A. Defective low-pressure cutout or thermostat differential set too narrow
B. Oversized condenser water pump motor
C. Excessive refrigerant subcooling
D. High oil return velocity in the suction line
🟢 A. Defective low-pressure cutout or thermostat differential set too narrow
🔴 RATIONALE: A narrow differential or a failing pressure switch causes the compressor to satisfy
load requirements and shut down too quickly, leading to rapid restarts and equipment wear.
