HVAC HVAC Troubleshooting Techniques 5

Question 1

A rooftop unit supply air temperature is 58°F but the leaving water temperature from the chiller is correct at 44°F. What is the MOST likely cause of the warm supply air?

Accepted Answer

Chilled water control valve is not opening fully

Answer

If chilled water supply temperature is correct but the coil is not cooling adequately, the control valve is restricting water flow through the coil, reducing heat transfer.

Question 2

A technician uses an electronic refrigerant detector and gets a strong signal near the compressor crankcase. What should the technician do to confirm the leak location?

Accepted Answer

Apply nitrogen pressure and use soap bubbles or UV dye to pinpoint the exact leak site

Answer

Electronic detectors identify general leak areas, but nitrogen pressure combined with soap solution or UV dye is needed to pinpoint the exact leak location before repair.

Question 3

A customer reports that their ductless heat pump's heating capacity drops significantly when outdoor temperature falls below 35°F. This is MOST likely caused by:

Accepted Answer

The normal thermodynamic reduction in heat pump heating capacity at low outdoor temperatures

Answer

Heat pump heating capacity naturally decreases as outdoor temperature drops because less heat energy is available to absorb from cold outdoor air—this is normal operation, not a fault.

Question 4

After replacing a compressor, a technician pulls a vacuum to 500 microns and the system holds for 15 minutes. The technician then charges the system and it trips the high-pressure switch. What was MOST likely missed during the compressor replacement?

Accepted Answer

The filter-drier was not replaced

Answer

Replacing a failed compressor without replacing the filter-drier leaves acid and contaminants in the system, which can cause the new compressor to fail or cause restriction that raises head pressure.

Question 5

A building's VAV system delivers poor cooling to perimeter offices in the afternoon despite adequate static pressure at the AHU. What is the MOST likely cause?

Accepted Answer

VAV box actuators in perimeter zones are failing to open due to solar heat gain overloading the zone controllers

Answer

Afternoon solar gain dramatically increases perimeter zone loads, and if the VAV boxes cannot fully open or are undersized for peak solar load, those zones will overheat despite adequate system pressure.

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC HVAC Troubleshooting Techniques 5