HVAC System Components & Diagnostics Flashcards

A chiller's approach temperature (difference between leaving chilled water and refrigerant saturation temperature) has increased from 2°F to 8°F. What is the most likely cause?

Answer: Fouled evaporator tubes reducing heat transfer efficiency

An increased approach temperature in the evaporator indicates fouled tubes reducing heat transfer, causing the refrigerant to remain colder relative to the leaving water.

Which of the following best describes the purpose of economizer mode in a commercial rooftop unit?

Answer: Reduces refrigerant compressor wear by limiting run hours when outdoor conditions allow free cooling

Economizer mode uses cool outdoor air for free cooling, reducing or eliminating mechanical refrigeration compressor run hours and energy consumption.

What does oil logging in an evaporator coil cause in a refrigeration system?

Answer: Reduced heat transfer efficiency and decreased system capacity

Oil logging in the evaporator coats the tube interior, reducing heat transfer efficiency and system capacity, while also reducing oil return to the compressor.

A technician is performing a standing pressure test on a newly installed refrigerant system. Which gas should be used for this test?

Answer: Nitrogen (dry, oil-free)

Dry nitrogen is the approved gas for pressure testing refrigerant systems because it is inert, non-flammable, and does not contaminate the system.

In a direct expansion (DX) cooling coil, what determines the dew point of the leaving supply air?

Answer: Refrigerant suction pressure and the coil's mean surface temperature

The coil surface temperature, driven by refrigerant suction pressure, determines how much moisture condenses and therefore the dew point of the leaving air.

A two-stage reciprocating compressor system uses an intercooler between stages. What is the primary function of the intercooler?

Answer: Remove superheat from the first-stage discharge gas before second-stage compression

The intercooler removes superheat from the first-stage discharge gas, reducing the temperature and volume entering the second stage, improving compression efficiency.

Which ASHRAE Standard governs minimum ventilation rates for acceptable indoor air quality in commercial buildings?

Answer: ASHRAE 62.1 – Ventilation for Acceptable Indoor Air Quality

ASHRAE Standard 62.1 specifies minimum outdoor air ventilation rates per occupant and per floor area to maintain acceptable indoor air quality in commercial buildings.