Critical Point
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The critical point (critical temperature and critical pressure) means the substance has gone above the point when there is no longer a boundary between liquid and gas.
A substance above its critical point is always in the gaseous state.
At temperatures below the critical point, all types of refrigerant in pressure canisters exhibit both a liquid and a gas phase, meaning there is a layer of gas above the liquid.
As long as there is still gas present in the container next to the fluid, pressure is dependent on ambient temperature. Refer to REFRIGERANT R134A VAPOR PRESSURE TABLE .
NOTE:
Different types of refrigerant are never to be mixed. Only the refrigerant designated for the corresponding A/C system may be used.