R-22 PT Chart: Pressure, Temperature and Worked Readings

Read a row as a saturation temperature and its matching gauge pressure. Psig is gauge pressure, not absolute pressure. Do not use this chart with a gauge set to psia. The Daikin chart labels its pressure units explicitly. Values between stored rows use straight-line interpolation; values outside the table are not covered.

Arkema’s manufacturer chart gives 68.6 psig at 40°F and 195.9 psig at 100°F. The stored table here gives 68.5 and 195.9. This is a reference comparison, not an instruction to change a charge to remove a tenth of a psi.

These are worked examples using the stored table, not target values for a particular unit.

Superheat = suction-line temperature − vapor saturation temperature. Subcooling = liquid saturation temperature − liquid-line temperature. Read the superheat method and subcooling method for where those measurements fit. These definitions are also shown in Fieldpiece’s SM380V operator’s manual linked below.

Write the measured pressure, selected refrigerant, saturation temperature and line temperature on the same job note. That leaves a checkable calculation instead of a bare result whose inputs have been lost.

At 76.25 psig, the stored R-22 table is halfway between 68.5 psig at 40°F and 84.0 psig at 50°F. Linear interpolation gives 45°F. A 57°F suction line then gives 12°F superheat.

The halfway shortcut works here because the pressure was chosen exactly halfway between the two stored rows. For any other reading, find the fraction of the pressure interval first, then apply that fraction to the temperature interval. The free calculator does that lookup. Do not extend the last interval beyond the published range.

An edge case: a pressure beyond the last table row must return an out-of-range message, not a guessed saturation temperature. A pressure reading of 999 psig is outside this table. Recheck the selected refrigerant and units before using any result.

A P-T chart answers “what saturation temperature goes with this pressure?” It does not answer “how much refrigerant should I add?” Keep those two questions separate. Record the lookup first, then use the unit’s charging instructions and target.

For the method choice, use our TXV and fixed-orifice guide. For another refrigerant, open its own table: R-454B bubble and dew or R-32. A similar-looking pressure is not permission to substitute a chart. Daikin’s reference explicitly says to use the refrigerant marked on the nameplate and not mix refrigerants.

When recording a job, keep the source chart with the readings. If a manufacturer value and an app value differ, compare refrigerant, units, liquid/vapor column and table spacing before treating either number as a diagnosis.