NCT HVAC System Components & Diagnostics 2

Question 1

A technician measures superheat at the evaporator outlet and finds it is only 2°F. What condition does this indicate?

Accepted Answer

Flooded evaporator with liquid refrigerant carry-over risk

Answer

A superheat of 2°F at the evaporator outlet indicates a flooded coil, risking liquid refrigerant slugging the compressor.

Question 2

Which type of heat exchanger is most commonly used as a condenser in air-cooled commercial HVAC systems?

Accepted Answer

Fin-and-tube coil with axial fans

Answer

Air-cooled condensers in commercial HVAC systems typically use fin-and-tube coils with axial fans to reject heat to the outdoor air.

Question 3

What is the primary purpose of a crankcase heater on a refrigerant compressor?

Accepted Answer

To prevent refrigerant migration and liquid slugging at startup

Answer

Crankcase heaters prevent refrigerant from migrating into the oil during the off cycle, which would cause oil foaming and slugging at startup.

Question 4

A variable air volume (VAV) box fails to modulate airflow. Which component should the technician inspect first?

Accepted Answer

Damper actuator and its control signal

Answer

The damper actuator is the primary modulating component of a VAV box, and a failed actuator or missing control signal is the most common cause of no modulation.

Question 5

During commissioning of a chilled water system, the technician notices the entering and leaving chilled water temperature difference (ΔT) is only 4°F instead of the design 10°F. What is the most likely cause?

Accepted Answer

Chilled water flow rate is too high

Answer

A low ΔT across the chiller evaporator typically indicates excessive chilled water flow rate, a common symptom of low ΔT syndrome.

(NCT) NAFA Certified Technician Practice Test

(NCT) NAFA Certified Technician Practice Test

NCT HVAC System Components & Diagnostics 2