HVAC Troubleshooting 4

Question 1

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?

Accepted Answer

Metering device stuck open or failed open

Answer

A metering device stuck open floods the evaporator, raising suction pressure and lowering superheat significantly.

Question 2

A residential heat pump operates correctly in cooling but has poor performance in heating mode. What should be suspected?

Accepted Answer

Defrost control malfunction

Answer

A faulty defrost control prevents the heat pump from clearing ice from the outdoor coil, drastically reducing heating capacity.

Question 3

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?

Accepted Answer

Contactor contacts

Answer

Burned or pitted contactor contacts may not pass current even when the contactor coil pulls in, preventing the compressor and fan from starting.

Question 4

An HVAC technician is troubleshooting a variable-speed air handler that is not communicating with the thermostat. What is the first step?

Accepted Answer

Verify 24V power at the air handler control board

Answer

Without 24V control voltage, the air handler's control board cannot operate or communicate, making power verification the essential first step.

Question 5

A gas furnace's pressure switch opens during operation. The flue pipe is clear and the inducer runs. What else should be checked?

Accepted Answer

Condensate drain trap and tubing to the pressure switch

Answer

A blocked condensate drain trap or kinked tubing to the pressure switch can cause a false negative-pressure reading, tripping the switch during operation.

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HVAC Troubleshooting 4