As pressure on a gas decreases, the gas expands and cools; increasing pressure makes the temperature rise. You could also express these phase changes as evaporation and condensation, which is how evaporator coils and condenser coils get their names. Refrigerants, including Freon and Puron, may never need recharging throughout the life of your AC.
1 Make sure that the start of the ruler is directly below the center of one eyeâs pupil. 2  Hold the ruler (keeping it steady and parallel to the floor); mark the location on the ruler of the other eyeâs pupil. 3  Measure the distance in millimeters between the two marks. 4  That distance will be your PD.
But, first things first: What The Pupillary Distance Is. Pupillary Distance (PD) or interpupillary distance (IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupils in each eye. This measurement is used when preparing to make prescription eyeglasses.