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How it Works: Pressure Switches
Air conditioning systems use pressure switches to regulate the pressure from within the system and serve the purpose of preventing component failure. Below are descriptions of some of the most common pressure switches.
Low Pressure Cut Out Switch (LPCO)
The LPCO is used to shut off the compressor if the air conditioning system drops below a certain pressure, indicating there is not enough refrigerant. It works by creating an open circuit to the electrical power supply that runs to the compressor and helps prevent compressor damage. The LPCO is wired in series to the circuitry.
High Pressure Cut out Switch (HPCO)
The HPCO is used to protect the system from excess pressure. If it senses the
pressure in the system is too high, it will create an open circuit to the electrical
power supply running to the compressor to prevent damage. The HPCO is wired in series to the circuitry.
High Pressure Relief Valve (Pop off valve)
These were quite common in early vehicles. They are located in the receiver drier, compressor and/or hoses and look like a raised round dot. High pressure relief valves are designed to release refrigerant into the atmosphere if the pressure in the system gets too high. They work via a series of internal springs. Once the pressure in the system returns to normal, the springs close.
Compressor Cycling Switch
The compressor cycling switch is used to control the compressor clutch and senses the pressure on the low side of the system, switching the compressor on when needed.
Fan Switch
This operates in the medium pressure range and is used to turn on/off the
condenser fan while the air conditioner is operating.
Thermo limiting Switch
This superheat switch has a fuse that will melt at a certain pressure. It works by
creating an open circuit to the electric power supply that runs to the compressor and prevents damage.
Low Pressure Cut Out Switch (LPCO)
The LPCO is used to shut off the compressor if the air conditioning system drops below a certain pressure, indicating there is not enough refrigerant. It works by creating an open circuit to the electrical power supply that runs to the compressor and helps prevent compressor damage. The LPCO is wired in series to the circuitry.
High Pressure Cut out Switch (HPCO)
The HPCO is used to protect the system from excess pressure. If it senses the
pressure in the system is too high, it will create an open circuit to the electrical
power supply running to the compressor to prevent damage. The HPCO is wired in series to the circuitry.
High Pressure Relief Valve (Pop off valve)
These were quite common in early vehicles. They are located in the receiver drier, compressor and/or hoses and look like a raised round dot. High pressure relief valves are designed to release refrigerant into the atmosphere if the pressure in the system gets too high. They work via a series of internal springs. Once the pressure in the system returns to normal, the springs close.
Compressor Cycling Switch
The compressor cycling switch is used to control the compressor clutch and senses the pressure on the low side of the system, switching the compressor on when needed.
Fan Switch
This operates in the medium pressure range and is used to turn on/off the
condenser fan while the air conditioner is operating.
Thermo limiting Switch
This superheat switch has a fuse that will melt at a certain pressure. It works by
creating an open circuit to the electric power supply that runs to the compressor and prevents damage.
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