Troubleshooting Flashcards
7 cards from real HVAC 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 flashcards as text
A technician notices that a system's high-side pressure is normal but the low-side pressure is higher than expected with low superheat. What is the most likely diagnosis?
Answer: Metering device stuck open or failed open
A metering device stuck open floods the evaporator, raising suction pressure and lowering superheat significantly.
A residential heat pump operates correctly in cooling but has poor performance in heating mode. What should be suspected?
Answer: Defrost control malfunction
A faulty defrost control prevents the heat pump from clearing ice from the outdoor coil, drastically reducing heating capacity.
During a service call, a technician measures 240V at a condenser but the unit does not start. The capacitor tests good. What should be checked next?
Answer: Contactor contacts
Burned or pitted contactor contacts may not pass current even when the contactor coil pulls in, preventing the compressor and fan from starting.
An HVAC technician is troubleshooting a variable-speed air handler that is not communicating with the thermostat. What is the first step?
Answer: Verify 24V power at the air handler control board
Without 24V control voltage, the air handler's control board cannot operate or communicate, making power verification the essential first step.
A gas furnace's pressure switch opens during operation. The flue pipe is clear and the inducer runs. What else should be checked?
Answer: Condensate drain trap and tubing to the pressure switch
A blocked condensate drain trap or kinked tubing to the pressure switch can cause a false negative-pressure reading, tripping the switch during operation.
Subcooling is measured at 22°F on an R-410A system with a TXV. What condition does this indicate?
Answer: Overcharge or restricted metering device
Subcooling above 15°F on a TXV system typically indicates an overcharge or a restriction in the metering device causing liquid to back up in the condenser.
A technician suspects a cracked heat exchanger in a gas furnace. Which test is the most reliable field method?
Answer: Combustion analysis of CO levels
Elevated carbon monoxide in the supply air or living space, verified with a combustion analyzer, is the most reliable indicator of a cracked heat exchanger allowing flue gases to enter the airstream.