|To use the HVAC Technical Support AC Pressure Temperature Chart,
- Turn unit on; monitor system running approximately 15 to 30 minutes. Take a reading of your refrigerant system pressure (PSIG).
- Find the corresponding saturated pressure for your refrigerant.
Superheat (for units with fixed metering device): Compute the superheat by determining saturated suction temperature from Temperature Pressure Chart. Subtract from actual suction line temperature before compressor. The manufacturers recommended superheat is usually listed in the installation instructions on on the units rating plate. If it is not listed use 15 degrees of superheat as a default.
Subcooling (for units with Thermostatic Expansion Valve or TXV): Compute subcooling by determining saturated condensing temperature from Temperature Pressure Chart. Subtract from liquid temperature entering TXV. The manufactures recommended subcooling is usually listed on units rating plate. If it is not listed use 15 degrees of subcooling as a default.