Pressure-temperature chart. Techs use it to turn a gauge reading into a saturation temperature, the starting point for superheat and subcooling. Blends with glide list separate bubble and dew columns. Digital manifolds have PT charts built in, and many techs also carry a pocket card. A system off for hours should sit near the PT pressure for the surrounding temperature, which is a quick check for non-condensables.
Pull out the PT chart, 410A at 340 psi is about 105 degrees, so with 85 outside our condenser split is 20.
Also heard as
- pressure-temperature chart
- PT card
- P/T chart
Related terms
Saturation
The state where liquid and vapor refrigerant coexist, so its temperature is locked to its pressure.
Glide
The temperature change of a refrigerant blend as it boils or condenses at constant pressure.
Non-condensables
Air, nitrogen or other gases trapped in a refrigeration system that will not condense at operating conditions.
Gauges
The manifold gauge set techs connect to service ports to read system pressures, saturation temperatures and charge.