DC Master Air Conditioning and Refrigeration
Mechanical Unlimited (311) Certification
Exam 2025-2026 Questions & Answers Graded
A+
Question 1: What is the primary purpose of a TXV (Thermostatic
Expansion Valve) in a refrigeration system?
Answer: To control the amount of refrigerant entering the evaporator and
maintain proper superheat.
Question 2: Which component in a refrigeration cycle rejects heat to the
outside air?
Answer: Condenser.
Question 3: What type of piping material is most commonly used for
refrigerant lines?
Answer: Copper tubing.
Question 4: According to ASHRAE Standard 62.1, what is the minimum
ventilation requirement for office spaces?
Answer: 20 cfm per person.
Question 5: Which refrigerant has zero ozone depletion potential and is
commonly used as a replacement for R-22?
Answer: R-410A.
,Question 6: In DC, which authority issues permits for HVAC
installations?
Answer: The Department of Consumer and Regulatory Affairs (DCRA).
Question 7: What is the typical color of a cylinder containing R-410A
refrigerant?
Answer: Rose/Pink.
Question 8: What is the function of a crankcase heater in a compressor?
Answer: It prevents refrigerant migration and mixing with oil during the
off cycle.
Question 9: What does SEER stand for in HVAC rating systems?
Answer: Seasonal Energy Efficiency Ratio.
Question 10: What electrical device protects motors from overload
conditions?
Answer: Thermal overload relay.
Question 11: A cooling load requires 24,000 BTU/hr. How many tons of
cooling is required?
Answer: 2 tons (since 1 ton = 12,000 BTU/hr).
,Question 12: If an air duct carries 2,000 CFM at a velocity of 800 FPM,
what is the duct cross-sectional area?
Answer: Area = CFM ÷ Velocity = 2000 ÷ 800 = 2.5 sq. ft.
Question 13: An air conditioning system supplies 1,200 CFM with an air
temperature rise of 30°F. How much heating capacity in BTU/hr is
provided? (Use 1.08 × CFM × ΔT)
Answer: Capacity = 1.08 × 1200 × 30 = 38,880 BTU/hr.
Question 14: A refrigeration system operates with a suction pressure of
68 psig (R-22). What is the approximate evaporating temperature?
Answer: Around 40°F (from R-22 pressure-temperature chart).
Question 15: A compressor draws 15 amps at 240V. What is the input
power in watts?
Answer: Power = V × I = 240 × 15 = 3,600 W.
Question 16: If a room has a sensible heat gain of 18,000 BTU/hr and a
latent heat gain of 6,000 BTU/hr, what is the total cooling load?
Answer: 24,000 BTU/hr (2 tons).
Question 17: A fan delivers 10,000 CFM at 2 inches of total static
pressure. What is the fan horsepower required if efficiency is 65%? (HP
= CFM × SP ÷ (6356 × Efficiency))
Answer: HP = 10000 × 2 ÷ (6356 × 0.65) ≈ 4.8 HP.
, Question 18: What is the superheat if the suction line temperature is 55°F
and the saturation temperature at suction pressure is 45°F?
Answer: Superheat = 55 – 45 = 10°F.
Question 19: A system requires 3 tons of cooling. How many BTU/hr
does this equal?
Answer: 36,000 BTU/hr.
Question 20: If the return air is 78°F DB and 62°F WB, and the supply
air is 58°F DB, what is the sensible heat ratio? (Use psychrometric chart
data).
Answer: Approximate SHR = 0.75 (sensible load dominates).
Question 21: What is the primary purpose of a TXV (Thermostatic
Expansion Valve) in a refrigeration system?
Answer: To control the amount of refrigerant entering the evaporator and
maintain proper superheat.
Question 22: Which component in a refrigeration cycle rejects heat to the
outside air?
Answer: Condenser.
Question 23: What type of piping material is most commonly used for
refrigerant lines?
Mechanical Unlimited (311) Certification
Exam 2025-2026 Questions & Answers Graded
A+
Question 1: What is the primary purpose of a TXV (Thermostatic
Expansion Valve) in a refrigeration system?
Answer: To control the amount of refrigerant entering the evaporator and
maintain proper superheat.
Question 2: Which component in a refrigeration cycle rejects heat to the
outside air?
Answer: Condenser.
Question 3: What type of piping material is most commonly used for
refrigerant lines?
Answer: Copper tubing.
Question 4: According to ASHRAE Standard 62.1, what is the minimum
ventilation requirement for office spaces?
Answer: 20 cfm per person.
Question 5: Which refrigerant has zero ozone depletion potential and is
commonly used as a replacement for R-22?
Answer: R-410A.
,Question 6: In DC, which authority issues permits for HVAC
installations?
Answer: The Department of Consumer and Regulatory Affairs (DCRA).
Question 7: What is the typical color of a cylinder containing R-410A
refrigerant?
Answer: Rose/Pink.
Question 8: What is the function of a crankcase heater in a compressor?
Answer: It prevents refrigerant migration and mixing with oil during the
off cycle.
Question 9: What does SEER stand for in HVAC rating systems?
Answer: Seasonal Energy Efficiency Ratio.
Question 10: What electrical device protects motors from overload
conditions?
Answer: Thermal overload relay.
Question 11: A cooling load requires 24,000 BTU/hr. How many tons of
cooling is required?
Answer: 2 tons (since 1 ton = 12,000 BTU/hr).
,Question 12: If an air duct carries 2,000 CFM at a velocity of 800 FPM,
what is the duct cross-sectional area?
Answer: Area = CFM ÷ Velocity = 2000 ÷ 800 = 2.5 sq. ft.
Question 13: An air conditioning system supplies 1,200 CFM with an air
temperature rise of 30°F. How much heating capacity in BTU/hr is
provided? (Use 1.08 × CFM × ΔT)
Answer: Capacity = 1.08 × 1200 × 30 = 38,880 BTU/hr.
Question 14: A refrigeration system operates with a suction pressure of
68 psig (R-22). What is the approximate evaporating temperature?
Answer: Around 40°F (from R-22 pressure-temperature chart).
Question 15: A compressor draws 15 amps at 240V. What is the input
power in watts?
Answer: Power = V × I = 240 × 15 = 3,600 W.
Question 16: If a room has a sensible heat gain of 18,000 BTU/hr and a
latent heat gain of 6,000 BTU/hr, what is the total cooling load?
Answer: 24,000 BTU/hr (2 tons).
Question 17: A fan delivers 10,000 CFM at 2 inches of total static
pressure. What is the fan horsepower required if efficiency is 65%? (HP
= CFM × SP ÷ (6356 × Efficiency))
Answer: HP = 10000 × 2 ÷ (6356 × 0.65) ≈ 4.8 HP.
, Question 18: What is the superheat if the suction line temperature is 55°F
and the saturation temperature at suction pressure is 45°F?
Answer: Superheat = 55 – 45 = 10°F.
Question 19: A system requires 3 tons of cooling. How many BTU/hr
does this equal?
Answer: 36,000 BTU/hr.
Question 20: If the return air is 78°F DB and 62°F WB, and the supply
air is 58°F DB, what is the sensible heat ratio? (Use psychrometric chart
data).
Answer: Approximate SHR = 0.75 (sensible load dominates).
Question 21: What is the primary purpose of a TXV (Thermostatic
Expansion Valve) in a refrigeration system?
Answer: To control the amount of refrigerant entering the evaporator and
maintain proper superheat.
Question 22: Which component in a refrigeration cycle rejects heat to the
outside air?
Answer: Condenser.
Question 23: What type of piping material is most commonly used for
refrigerant lines?
