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Louisiana New Orleans Second Class Stationary Air
Conditioning - 640-LA Contractor Exam Questions with
Correct Answers and explanations LATEST THIS YEAR -
JUST RELEASED
Louisiana New Orleans Second Class Stationary Air Conditioning - 640-LA Contractor
Exam Coverage Summary: Sensible and Latent Heat Calculations, PT Charts and Superheat/Subcooling,
Compressor Types (Reciprocating, Scroll, Screw, Centrifugal), Evaporators and Condensers, Cooling
Towers, Refrigerant Safety Groups (ASHRAE 34), EPA 608 Regulations, Brazing and Pressure Testing,
Electrical Theory (Ohms Law) and Components, Vacuum and Dehydration, Metering Devices (TXV, Cap
Tube), Oil Management, Local Amendments to IMC.
1. You are on a jobsite in New Orleans replacing a 35-ton chiller. The old unit used R-22, but the new
unit uses R-410A. Regarding the piping, what critical change must be made to the service hoses and
manifold gauges?
A) The hoses must be longer to reach the new service valves
B) The hoses must have standard brass fittings, as they are universal
C) The hoses must be rated for higher pressure, specifically 800 psi working pressure
D) The hoses must be made of aluminum to prevent rust due to humidity
*Rationale: R-410A operates at significantly higher pressures (50-60% higher) than R-22. Standard R-22
gauges/hoses can rupture; 800 psi rated equipment is required for safety .*
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2. A technical manual specifies that a compressor is a "Reciprocating" type. Which mechanical action
defines this compressor's operation?
A) Two intermeshing screws rotating to trap and compress gas
B) An orbiting scroll meshing with a fixed scroll to compress gas
C) A piston moving back and forth inside a cylinder to compress gas
D) An impeller spinning at high speed to throw gas outward
Rationale: Reciprocating compressors use pistons driven by a crankshaft (like a car engine). Screw uses
rotors, Scroll uses an orbiting plate, and Centrifugal uses an impeller .
3. The metering device on a 50-ton air handler is being replaced. The technician installs a Thermostatic
Expansion Valve (TXV). What is the primary function of the TXV in this system?
A) To reverse the flow of refrigerant for defrost cycle
B) To meter the flow of liquid refrigerant into the evaporator and maintain superheat
C) To store excess liquid refrigerant during low load conditions
D) To filter debris and moisture out of the liquid line
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Rationale: The TXV modulates the valve opening to maintain a constant superheat at the evaporator
outlet, ensuring the evaporator is fully active without liquid slugging the compressor .
4. During a system evacuation, you pull a vacuum down to 1000 microns and then close the vacuum
pump valve. The pressure rises quickly to 5000 microns within 2 minutes. What does this indicate?
A) The system is completely dry and ready for charging
B) The vacuum pump oil needs to be changed
C) There is moisture boiling off or a significant leak present
D) The micron gauge is defective
*Rationale: A rapid rise in pressure (decay) indicates that moisture is still boiling off (if it stabilizes near
2000-3000) or there is a large leak (if it rises to atmospheric quickly). A stable vacuum indicates a tight
system .*
5. A new rooftop unit is being installed. According to the International Mechanical Code (IMC) as
adopted by Louisiana, what is typically required for refrigerant piping passing through a concrete
foundation wall?
A) The pipe must be welded directly to the rebar
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B) The pipe must be enclosed in a corrosion-resistant sleeve and sealed
C) The pipe must be encased in spray foam insulation only
D) The pipe must be Schedule 80 black iron
Rationale: Passing refrigerant lines through a foundation requires a sleeve to protect the pipe from
shifting concrete and corrosion, and to provide a space for sealant .
6. You are inspecting a condenser. The "Discharge Line" leaves the compressor and goes to the
condenser. Which of the following best describes the state of the refrigerant in this line immediately
after a properly functioning compressor in a comfort-cooling system?
A) Low pressure, low temperature vapor
B) High pressure, low temperature liquid
C) High pressure, high temperature superheated vapor
D) Low pressure, high temperature liquid
Rationale: The compressor takes low-pressure vapor and compresses it, resulting in a high-pressure,
high-temperature "superheated" vapor, which is then piped to the condenser .
Louisiana New Orleans Second Class Stationary Air
Conditioning - 640-LA Contractor Exam Questions with
Correct Answers and explanations LATEST THIS YEAR -
JUST RELEASED
Louisiana New Orleans Second Class Stationary Air Conditioning - 640-LA Contractor
Exam Coverage Summary: Sensible and Latent Heat Calculations, PT Charts and Superheat/Subcooling,
Compressor Types (Reciprocating, Scroll, Screw, Centrifugal), Evaporators and Condensers, Cooling
Towers, Refrigerant Safety Groups (ASHRAE 34), EPA 608 Regulations, Brazing and Pressure Testing,
Electrical Theory (Ohms Law) and Components, Vacuum and Dehydration, Metering Devices (TXV, Cap
Tube), Oil Management, Local Amendments to IMC.
1. You are on a jobsite in New Orleans replacing a 35-ton chiller. The old unit used R-22, but the new
unit uses R-410A. Regarding the piping, what critical change must be made to the service hoses and
manifold gauges?
A) The hoses must be longer to reach the new service valves
B) The hoses must have standard brass fittings, as they are universal
C) The hoses must be rated for higher pressure, specifically 800 psi working pressure
D) The hoses must be made of aluminum to prevent rust due to humidity
*Rationale: R-410A operates at significantly higher pressures (50-60% higher) than R-22. Standard R-22
gauges/hoses can rupture; 800 psi rated equipment is required for safety .*
, Page 2 of 143
2. A technical manual specifies that a compressor is a "Reciprocating" type. Which mechanical action
defines this compressor's operation?
A) Two intermeshing screws rotating to trap and compress gas
B) An orbiting scroll meshing with a fixed scroll to compress gas
C) A piston moving back and forth inside a cylinder to compress gas
D) An impeller spinning at high speed to throw gas outward
Rationale: Reciprocating compressors use pistons driven by a crankshaft (like a car engine). Screw uses
rotors, Scroll uses an orbiting plate, and Centrifugal uses an impeller .
3. The metering device on a 50-ton air handler is being replaced. The technician installs a Thermostatic
Expansion Valve (TXV). What is the primary function of the TXV in this system?
A) To reverse the flow of refrigerant for defrost cycle
B) To meter the flow of liquid refrigerant into the evaporator and maintain superheat
C) To store excess liquid refrigerant during low load conditions
D) To filter debris and moisture out of the liquid line
, Page 3 of 143
Rationale: The TXV modulates the valve opening to maintain a constant superheat at the evaporator
outlet, ensuring the evaporator is fully active without liquid slugging the compressor .
4. During a system evacuation, you pull a vacuum down to 1000 microns and then close the vacuum
pump valve. The pressure rises quickly to 5000 microns within 2 minutes. What does this indicate?
A) The system is completely dry and ready for charging
B) The vacuum pump oil needs to be changed
C) There is moisture boiling off or a significant leak present
D) The micron gauge is defective
*Rationale: A rapid rise in pressure (decay) indicates that moisture is still boiling off (if it stabilizes near
2000-3000) or there is a large leak (if it rises to atmospheric quickly). A stable vacuum indicates a tight
system .*
5. A new rooftop unit is being installed. According to the International Mechanical Code (IMC) as
adopted by Louisiana, what is typically required for refrigerant piping passing through a concrete
foundation wall?
A) The pipe must be welded directly to the rebar
, Page 4 of 143
B) The pipe must be enclosed in a corrosion-resistant sleeve and sealed
C) The pipe must be encased in spray foam insulation only
D) The pipe must be Schedule 80 black iron
Rationale: Passing refrigerant lines through a foundation requires a sleeve to protect the pipe from
shifting concrete and corrosion, and to provide a space for sealant .
6. You are inspecting a condenser. The "Discharge Line" leaves the compressor and goes to the
condenser. Which of the following best describes the state of the refrigerant in this line immediately
after a properly functioning compressor in a comfort-cooling system?
A) Low pressure, low temperature vapor
B) High pressure, low temperature liquid
C) High pressure, high temperature superheated vapor
D) Low pressure, high temperature liquid
Rationale: The compressor takes low-pressure vapor and compresses it, resulting in a high-pressure,
high-temperature "superheated" vapor, which is then piped to the condenser .
