If a refrigeration compressor using a thermostat as a primary controller is running continuously without significantly lowering the temperature in the refrigerated space, which of the following is most likely the trouble?

Correct Answer: Option D — a shortage of refrigerant

A shortage of refrigerant severely diminishes latent heat absorption in the evaporator. Because the evaporator lacks sufficient refrigerant mass to produce a cooling effect, the refrigerated space remains warm and the thermostat maintains continuous compressor operation.