Louisiana New Orleans 640-LA Second Class Stationary A/C Contractor Exam 2026 – Actual Questions & Verified Solutions | Latest Updated Test Bank + Study Guide

Louisiana New Orleans 640-LA Second Class
Stationary A/C Contractor Exam 2026 – Actual
Questions & Verified Solutions | Latest
Updated Test Bank + Study Guide
LOUISIANA NEW ORLEANS 640-LA

SECOND CLASS STATIONARY A/C CONTRACTOR EXAM 2026

QUESTIONS — VERIFIED SOLUTIONS & STUDY GUIDE


Question 1 What is the primary purpose of a refrigerant in an air conditioning system?

A. To lubricate compressor components

B. To filter contaminants from the air
C. To absorb heat from one location and release it at another

D. To control electrical voltage in the system

E. To regulate airflow through ductwork

CORRECT ANSWER: C. To absorb heat from one location and release it at
another

RATIONALE: Refrigerant is the working fluid in any refrigeration or air conditioning
cycle. It undergoes phase changes — evaporating at low pressure to absorb heat from
the conditioned space, and condensing at high pressure to release that heat to the
outdoors. This heat transfer process is the foundation of all vapor-compression
refrigeration systems. Without this property, no mechanical cooling could occur.



Question 2 Which refrigerant cycle law states that heat naturally flows from a warmer
body to a cooler body?

A. Boyle's Law
B. Charles's Law

C. Dalton's Law

D. The Second Law of Thermodynamics

E. Ohm's Law

CORRECT ANSWER: D. The Second Law of Thermodynamics

,RATIONALE: The Second Law of Thermodynamics establishes that heat energy
spontaneously flows from higher temperature regions to lower temperature regions.
This principle is what makes mechanical refrigeration necessary — to move heat from a
cool space to a warmer outdoor environment requires work input, which is provided by
the compressor. Understanding this law is essential for any refrigeration technician.



Question 3 What happens to the boiling point of a refrigerant when pressure is
increased?

A. The boiling point decreases
B. The boiling point remains unchanged

C. The boiling point increases

D. The refrigerant solidifies immediately

E. The refrigerant becomes non-condensable

CORRECT ANSWER: C. The boiling point increases

RATIONALE: There is a direct relationship between pressure and the boiling point of
any liquid, including refrigerants. When pressure increases, the boiling point rises. This
principle is exploited in refrigeration systems — the high-pressure side forces the
refrigerant to condense at elevated temperatures so heat can be rejected outdoors,
while the low-pressure side allows it to boil at lower temperatures to absorb indoor heat.
Pressure-temperature charts are used daily by technicians based on this principle.


Question 4 In a standard vapor-compression refrigeration cycle, which component
causes the refrigerant pressure to drop rapidly?
A. Compressor

B. Condenser

C. Evaporator

D. Metering device (expansion valve or capillary tube)

E. Accumulator

CORRECT ANSWER: D. Metering device (expansion valve or capillary tube)

RATIONALE: The metering device — whether a thermostatic expansion valve (TXV),
an automatic expansion valve (AXV), or a capillary tube — is designed to restrict

,refrigerant flow, causing a dramatic pressure drop. This pressure reduction causes the
refrigerant temperature to fall far below the temperature of the space being cooled,
enabling heat absorption in the evaporator. It is the dividing point between the high-
pressure and low-pressure sides of the system.


Question 5 Which of the following best defines "superheat" in refrigeration terminology?

A. The temperature of refrigerant in the condenser above ambient

B. The heat added to refrigerant vapor above its saturation temperature at a given
pressure

C. The total heat content of liquid refrigerant
D. The temperature differential across the condenser coil

E. The heat removed from refrigerant during compression

CORRECT ANSWER: B. The heat added to refrigerant vapor above its
saturation temperature at a given pressure

RATIONALE: Superheat is the additional heat energy added to a refrigerant after it has
fully vaporized. It is measured as the difference between the actual vapor temperature
and the saturation temperature corresponding to the suction pressure. Proper superheat
(typically 10–15°F at the evaporator outlet) ensures no liquid refrigerant enters the
compressor, which would cause serious mechanical damage known as "slugging."
Technicians measure superheat routinely during system charging.


Question 6 What is "subcooling" in a refrigeration system?

A. The cooling of suction vapor before entering the compressor

B. Cooling of liquid refrigerant below its saturation temperature at a given pressure

C. Cooling of air below the dew point

D. The reduction in compressor head pressure

E. Lowering refrigerant pressure in the condenser

CORRECT ANSWER: B. Cooling of liquid refrigerant below its saturation
temperature at a given pressure
RATIONALE: Subcooling refers to reducing liquid refrigerant temperature below its
condensing (saturation) temperature at the existing high-side pressure. Adequate

, subcooling (typically 10–20°F) ensures that only liquid — not a mixture of liquid and
vapor — enters the metering device, which improves system efficiency and prevents
flash gas formation at the expansion device inlet. Insufficient subcooling results in poor
system capacity and uneven refrigerant distribution.


Question 7 R-410A refrigerant is classified as which type?

A. Chlorofluorocarbon (CFC)

B. Hydrochlorofluorocarbon (HCFC)

C. Hydrofluorocarbon (HFC)

D. Natural refrigerant

E. Hydrocarbon blend

CORRECT ANSWER: C. Hydrofluorocarbon (HFC)

RATIONALE: R-410A is an HFC refrigerant — it contains hydrogen, fluorine, and
carbon but no chlorine. Because it contains no chlorine, it has zero ozone-depleting
potential (ODP). However, it has a high global warming potential (GWP) of
approximately 2,088. R-410A replaced R-22 (an HCFC) as the standard residential A/C
refrigerant. HFCs are regulated under the Kigali Amendment to the Montreal Protocol
due to their climate impact.



Question 8 What is the approximate Global Warming Potential (GWP) of R-410A
compared to CO₂?

A. 100
B. 410

C. 1,000

D. 2,088

E. 4,500

CORRECT ANSWER: D. 2,088

RATIONALE: R-410A has a GWP of approximately 2,088, meaning it has over 2,000
times the atmospheric warming effect of carbon dioxide (CO₂) per unit mass over a 100-
year period. This high GWP is a significant environmental concern, which is why the
industry is transitioning toward lower-GWP alternatives such as R-32 and R-454B.