The safety device that is used to start the compressor when excessively high head pressure develops is called what?

The correct answer describes a safety device designed to protect the compressor from damage due to excessively high head pressure. A spring loaded relief valve is engineered to open at a predetermined pressure level, allowing excess refrigerant or pressure to escape. This release helps to prevent reaching a critical pressure level that could lead to mechanical failure or unsafe operating conditions.

In the context of refrigeration and HVAC systems, maintaining appropriate pressure levels is crucial for optimal performance and safety. When head pressure rises excessively, the spring loaded relief valve activates, ensuring that the system remains within safe operating limits. This prevents potential damage to the compressor and the entire refrigeration system.

The other options do not serve the same purpose. A pressure switch is typically used for monitoring and controlling pressure levels but does not directly relieve excessive pressure. A thermostatic expansion valve regulates refrigerant flow based on temperature, not pressure. An overload protector is a device designed to prevent motor overload by cutting power if too much current is drawn but does not address high pressure situations directly.