In an air conditioning system, refrigerant are present in three forms:
As the refrigerant passes through the expansion device, the refrigerant once again changes into liquid/vapor mixture and continues to stay in this state through most of the evaporator coil. Near the exit point of the evaporator and entrance to the suction line, the refrigerant has changed to all vapor once again.
Remember - when using your PT chart as a diagnostics tool, it only pertains to the refrigerant in the liquid/vapor state, meaning the refrigerant in the condenser and evaporator coils. When the refrigerant exists in a liquid and vapor state, it is in a condition called saturated.
Superheat and Subcooling Superheat is measured at the places where the only vapor is present (the suction line) and is the difference between the saturation temperature and the measured temperature. In a properly operating HVAC system, the measured temperature will always be above the saturation temperature, usually 5-20F depending on the manufacturer and system conditions.
Subcooling is measured at the places where only liquid is present (the liquid line) and is the difference between the saturation temperature and the measured temperature. In a properly operating HVAC system, the measured temperature will always be below the saturation temperature, usually 5-15F depending on the manufacturer and system conditions.
So, if we can determine the pressure at any of the points where the refrigerant is in the saturated state, we can find the corresponding saturation temperature on our PT chart. You can even determine the pressure of the refrigerant in the saturated state by measuring the temperature, although it is much easier and more convenient to measure the pressures.
If you would like to become an HVAC technician and learn more about refrigeration and refrigerant, sign up for our online HVAC course. We have interactive superheat and subcooling exercises for measuring superheat and subcooling.
by Ron Walker
- Liquid
- Vapor
- Mixture of liquid and vapor
As the refrigerant passes through the expansion device, the refrigerant once again changes into liquid/vapor mixture and continues to stay in this state through most of the evaporator coil. Near the exit point of the evaporator and entrance to the suction line, the refrigerant has changed to all vapor once again.
Remember - when using your PT chart as a diagnostics tool, it only pertains to the refrigerant in the liquid/vapor state, meaning the refrigerant in the condenser and evaporator coils. When the refrigerant exists in a liquid and vapor state, it is in a condition called saturated.
Superheat and Subcooling Superheat is measured at the places where the only vapor is present (the suction line) and is the difference between the saturation temperature and the measured temperature. In a properly operating HVAC system, the measured temperature will always be above the saturation temperature, usually 5-20F depending on the manufacturer and system conditions.
Subcooling is measured at the places where only liquid is present (the liquid line) and is the difference between the saturation temperature and the measured temperature. In a properly operating HVAC system, the measured temperature will always be below the saturation temperature, usually 5-15F depending on the manufacturer and system conditions.
So, if we can determine the pressure at any of the points where the refrigerant is in the saturated state, we can find the corresponding saturation temperature on our PT chart. You can even determine the pressure of the refrigerant in the saturated state by measuring the temperature, although it is much easier and more convenient to measure the pressures.
If you would like to become an HVAC technician and learn more about refrigeration and refrigerant, sign up for our online HVAC course. We have interactive superheat and subcooling exercises for measuring superheat and subcooling.
by Ron Walker