Troubleshooting and System Diagnosis Flashcards
7 cards from real 313D practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Troubleshooting and System Diagnosis flashcards as text
A technician measures suction pressure significantly above normal and discharge pressure below normal on a residential split system. What is the most likely cause?
Answer: Compressor valve failure
Compressor valve failure causes high suction and low discharge pressure because refrigerant bypasses the compressor valves instead of being properly compressed.
During a service call, a homeowner reports the system runs continuously but never reaches setpoint. The evaporator coil is partially frosted. What should the technician check first?
Answer: Airflow across the evaporator coil
Restricted airflow is the most common cause of evaporator coil frosting and inadequate cooling, and should be checked before electrical components.
A technician finds the high-pressure switch tripping repeatedly on a hot day. Condenser coil appears clean. What is the next most likely cause?
Answer: Condenser fan motor failure or reduced airflow
A faulty or undersized condenser fan results in inadequate heat rejection, causing head pressure to rise and trip the high-pressure switch.
What does a high superheat AND high subcooling reading together most likely indicate?
Answer: Restriction in the liquid line or metering device
High subcooling indicates liquid refrigerant is backing up before a restriction, while high superheat indicates insufficient refrigerant reaching the evaporator.
A technician suspects a refrigerant leak. After recovering and recharging, what is the correct procedure before returning the system to service?
Answer: Pressurize with nitrogen and perform a leak test
After any repair, the system must be pressure-tested with nitrogen to confirm the repair is leak-free before evacuation and recharge.
A residential system has correct refrigerant charge but the supply air temperature differential (delta-T) is only 10°F instead of the expected 16–22°F. What is the most likely cause?
Answer: Excessive airflow across the evaporator
Too much airflow across the evaporator reduces the time the air has to exchange heat, resulting in a lower temperature differential.
When using an electronic leak detector and no leak is found at suspected areas, what technique should the technician use next?
Answer: Use UV dye and a UV light to locate the leak
UV dye inspection is an effective secondary method to locate leaks that electronic detectors may miss, especially slow or intermittent leaks.