If the compressor is not running, what component could be preventing it from engaging?

The pressure cycling switch is a crucial component in the air conditioning system that monitors the refrigerant pressure. Its primary function is to ensure that the compressor operates only under the correct pressure conditions to prevent any damage. If the pressure is too low, which can occur due to refrigerant leaks or insufficient refrigerant, the switch will prevent the compressor from engaging to avoid further issues such as compressor failure.

When the pressure cycling switch detects a condition that falls outside of its set parameters, it will open the circuit, effectively cutting power to the compressor and preventing it from running. This safety feature is vital for protecting the compressor and maintaining the system's overall integrity.

The other components mentioned, while essential for the operation of the HVAC system, do not have the same direct role in preventing the compressor from engaging under abnormal pressure conditions that the pressure cycling switch does.