Troubleshooting Flashcards

A rooftop packaged unit condenser fan motor fails in summer. What will happen to system operation if ignored?

Answer: Head pressure will rise, potentially tripping the high-pressure switch or damaging the compressor

Without condenser airflow, heat rejection fails, causing discharge pressure to rise until the high-pressure cutout trips or the system sustains damage.

A technician recovers refrigerant from a system, then pulls a deep vacuum and the vacuum rises rapidly when the pump is isolated. What does this indicate?

Answer: There is a leak or residual moisture in the system

A rising vacuum after pump isolation indicates either a system leak (air entering) or moisture boiling off, both requiring remediation before recharge.

What is the significance of measuring temperature difference (TD) across an evaporator coil during troubleshooting?

Answer: TD measures airflow adequacy and coil heat transfer effectiveness

The temperature difference between air entering and leaving the evaporator reflects airflow volume and coil efficiency; abnormal TD suggests airflow or coil problems.

A refrigeration system uses a capillary tube metering device and is suspected of being undercharged. How is the charge typically verified on this type of system?

Answer: By weighing in the exact factory charge after a complete evacuation

Capillary tube systems are critically charge-sensitive and are best charged by weighing the exact factory specification into an evacuated system.

During troubleshooting, a technician finds that the contactor coil is energized but the compressor does not start. The compressor hums briefly then the internal overload trips. What is the most likely cause?

Answer: Single-phasing (loss of one leg of power) or failed start components

A compressor that hums but fails to start and trips its overload is typically experiencing single-phasing or has failed start capacitors/relays preventing proper motor starting.

A technician suspects a hermetic compressor has an internal motor winding short. Which instrument confirms this diagnosis?

Answer: Megohmmeter (megger) or ohmmeter measuring winding resistance

A megohmmeter measures insulation resistance between windings and ground, confirming a winding short or ground fault in a hermetic compressor motor.

What condition is indicated when a system's sight glass shows clear liquid but system pressures are abnormal (low suction, high discharge)?

Answer: The sight glass location may be downstream of a restriction masking low charge

A restriction such as a blocked filter-drier upstream of the sight glass can back up liquid and show a clear glass even when charge is insufficient.