What symptom would you expect if the blower motor runs while HP/LP safety devices are open and the compressor is not?

What symptom would you expect if the blower motor runs while HP/LP safety devices are open and the compressor is not?

• A. Blower motor runs; compressor and condenser fan do not run
• B. Compressor runs; blower motor stops
• C. Condenser fan runs
• D. Thermostat fails open

Answer: (A)

When the high-pressure and low-pressure safety switches are open, they prevent the outdoor unit’s compressor from starting to protect the system. The indoor blower, on the other hand, can still be energized through the indoor control circuit if the thermostat or fan relay is calling for air movement. So you’d see the blower motor running, but the compressor and the condenser fan in the outdoor unit would not start because the safety switches keep the outdoor unit shut down. This matches the scenario described: indoor air is circulated, but the outdoor compressor and condenser fan remain off.

When the high-pressure and low-pressure safety switches are open, they prevent the outdoor unit’s compressor from starting to protect the system. The indoor blower, on the other hand, can still be energized through the indoor control circuit if the thermostat or fan relay is calling for air movement. So you’d see the blower motor running, but the compressor and the condenser fan in the outdoor unit would not start because the safety switches keep the outdoor unit shut down. This matches the scenario described: indoor air is circulated, but the outdoor compressor and condenser fan remain off.