HVAC System Components & Diagnostics Flashcards

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

Answer: Flooded evaporator with liquid refrigerant carry-over risk

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

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

Answer: Fin-and-tube coil with axial fans

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

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

Answer: To prevent refrigerant migration and liquid slugging at startup

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

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

Answer: Damper actuator and its control signal

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.

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?

Answer: Chilled water flow rate is too high

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

Which refrigerant circuit component prevents high-pressure liquid from flashing to vapor before reaching the metering device?

Answer: Subcooler or liquid-to-suction heat exchanger

A subcooler or liquid-to-suction heat exchanger adds subcooling to the liquid refrigerant, preventing flash gas formation before the metering device.

A rooftop unit's economizer damper remains fully open on a hot, humid day. Which component is most likely malfunctioning?

Answer: Enthalpy sensor or economizer controller

The enthalpy sensor or economizer controller determines whether outdoor conditions are suitable for free cooling; a faulty sensor can cause the damper to stay open inappropriately.