Pressure switches are safety devices designed to ensure that HVAC systems are not damaged by high or low pressure caused by the compressor and/or the refrigerant’s heat transference process. Located on the condensing unit in air conditioning and heat pump systems, pressure switches automatically stop system operations when they detect high or low pressure. High pressure switches typically stop the compressor circuit and need to be manually reset to start the air conditioner or heat pump. This is to ensure that the potential problem is properly addressed. High pressure is most often caused by a bad condenser fan motor, dirty or damaged condenser coils, or blockage of the refrigerant. Most low-pressure switches reset themselves if normal pressure resumes. Typical low-pressure causes include refrigerant leak, blower motor failure, air flow blockage, and plugged evaporator coils.