It is primarily a safety device which differs from the low-pressure control. Its sensing bulb is connected to a service valve on the discharge line by a flare nut. When the head pressure in the system approaches a dangerous level, it will automatically shut off the electrical power to prevent a compressor burnout through overheating.
In many commercial units, depending on the type of refrigerant being used, the cut-out pressure is never set higher than 300 psi to prevent damage to the system. As a rule of thumb, the high-pressure control is usually set to cut out the power at about 20% above normal head pressure, which is 165 psi for units using R-12, 275 psi for units using R-22, 200 psi for units using R-500, and 295 psi for units using R-502. Some units use a combination high- and low-pressure control. (See fig. 93)