NYC Mechanical Engineer (DCAS) — Certification
Practice Exam Questions With Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf A+ Grade Guarantee Verified
By Professionals
1.
A centrifugal pump in a closed-loop hydronic system shows reduced flow but
normal discharge pressure. The most likely cause is:
A. Cavitation at the impeller
B. Air trapped in the system
C. Excessive motor voltage
D. Oversized discharge piping
Correct Answer: B — ✔
Rationale: Air entrapment in a hydronic system can reduce effective flow while
maintaining apparent discharge pressure due to system resistance and
compressibility effects.
2.
Which HVAC control strategy is most effective for reducing simultaneous heating
and cooling?
A. Constant air volume (CAV)
B. Dual duct system
C. Variable air volume (VAV) with reheat lockout
D. Fixed speed fan operation
,Correct Answer: C — ✔
Rationale: A VAV system with reheat lockout minimizes energy waste by
preventing heating and cooling from operating simultaneously.
3.
A boiler exhibits short cycling. Which condition is the most probable cause?
A. Oversized boiler relative to load
B. Excessively low fuel pressure
C. High stack temperature
D. Excess combustion air
Correct Answer: A — ✔
Rationale: An oversized boiler reaches setpoint too quickly, causing frequent on/off
cycling.
4.
What is the primary function of a building’s expansion tank in a hydronic system?
A. Increase pump discharge pressure
B. Remove dissolved oxygen
C. Accommodate thermal expansion of water
D. Prevent pipe corrosion
Correct Answer: C — ✔
Rationale: Expansion tanks absorb volume changes due to thermal expansion of
water in closed systems.
5.
Which device is used to prevent backflow in potable water systems?
A. Gate valve
B. Check valve
,C. Balancing valve
D. Pressure regulator
Correct Answer: B — ✔
Rationale: A check valve allows one-way flow, preventing contamination from
reverse flow.
6.
In psychrometrics, relative humidity is defined as:
A. Actual vapor pressure divided by saturation vapor pressure
B. Dry bulb minus wet bulb temperature
C. Mass of water vapor per cubic meter
D. Total enthalpy of air mixture
Correct Answer: A — ✔
Rationale: Relative humidity is the ratio of actual moisture content to maximum
possible at saturation.
7.
A steam trap is primarily used to:
A. Increase steam pressure
B. Remove condensate without losing steam
C. Regulate boiler firing rate
D. Reduce superheat temperature
Correct Answer: B — ✔
Rationale: Steam traps discharge condensate while retaining live steam in the
system.
8.
, Which refrigeration cycle component lowers refrigerant pressure?
A. Compressor
B. Evaporator
C. Expansion valve
D. Condenser
Correct Answer: C — ✔
Rationale: The expansion valve reduces pressure, causing refrigerant cooling.
9.
A VAV box damper fails to open fully. The most likely impact is:
A. Increased static pressure upstream
B. Reduced zone airflow
C. Higher refrigerant charge
D. Increased boiler efficiency
Correct Answer: B — ✔
Rationale: A restricted damper reduces airflow delivery to the zone.
10.
Which law governs the relationship between pressure and volume of a gas at
constant temperature?
A. Boyle’s Law
B. Charles’s Law
C. Dalton’s Law
D. Newton’s Law
Correct Answer: A — ✔
Rationale: Boyle’s Law states pressure is inversely proportional to volume at
constant temperature.
Practice Exam Questions With Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf A+ Grade Guarantee Verified
By Professionals
1.
A centrifugal pump in a closed-loop hydronic system shows reduced flow but
normal discharge pressure. The most likely cause is:
A. Cavitation at the impeller
B. Air trapped in the system
C. Excessive motor voltage
D. Oversized discharge piping
Correct Answer: B — ✔
Rationale: Air entrapment in a hydronic system can reduce effective flow while
maintaining apparent discharge pressure due to system resistance and
compressibility effects.
2.
Which HVAC control strategy is most effective for reducing simultaneous heating
and cooling?
A. Constant air volume (CAV)
B. Dual duct system
C. Variable air volume (VAV) with reheat lockout
D. Fixed speed fan operation
,Correct Answer: C — ✔
Rationale: A VAV system with reheat lockout minimizes energy waste by
preventing heating and cooling from operating simultaneously.
3.
A boiler exhibits short cycling. Which condition is the most probable cause?
A. Oversized boiler relative to load
B. Excessively low fuel pressure
C. High stack temperature
D. Excess combustion air
Correct Answer: A — ✔
Rationale: An oversized boiler reaches setpoint too quickly, causing frequent on/off
cycling.
4.
What is the primary function of a building’s expansion tank in a hydronic system?
A. Increase pump discharge pressure
B. Remove dissolved oxygen
C. Accommodate thermal expansion of water
D. Prevent pipe corrosion
Correct Answer: C — ✔
Rationale: Expansion tanks absorb volume changes due to thermal expansion of
water in closed systems.
5.
Which device is used to prevent backflow in potable water systems?
A. Gate valve
B. Check valve
,C. Balancing valve
D. Pressure regulator
Correct Answer: B — ✔
Rationale: A check valve allows one-way flow, preventing contamination from
reverse flow.
6.
In psychrometrics, relative humidity is defined as:
A. Actual vapor pressure divided by saturation vapor pressure
B. Dry bulb minus wet bulb temperature
C. Mass of water vapor per cubic meter
D. Total enthalpy of air mixture
Correct Answer: A — ✔
Rationale: Relative humidity is the ratio of actual moisture content to maximum
possible at saturation.
7.
A steam trap is primarily used to:
A. Increase steam pressure
B. Remove condensate without losing steam
C. Regulate boiler firing rate
D. Reduce superheat temperature
Correct Answer: B — ✔
Rationale: Steam traps discharge condensate while retaining live steam in the
system.
8.
, Which refrigeration cycle component lowers refrigerant pressure?
A. Compressor
B. Evaporator
C. Expansion valve
D. Condenser
Correct Answer: C — ✔
Rationale: The expansion valve reduces pressure, causing refrigerant cooling.
9.
A VAV box damper fails to open fully. The most likely impact is:
A. Increased static pressure upstream
B. Reduced zone airflow
C. Higher refrigerant charge
D. Increased boiler efficiency
Correct Answer: B — ✔
Rationale: A restricted damper reduces airflow delivery to the zone.
10.
Which law governs the relationship between pressure and volume of a gas at
constant temperature?
A. Boyle’s Law
B. Charles’s Law
C. Dalton’s Law
D. Newton’s Law
Correct Answer: A — ✔
Rationale: Boyle’s Law states pressure is inversely proportional to volume at
constant temperature.
