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.
Average PD is about 62mm and most people fall within the 48 to 74 range but average PD for adults is from 54 to 68 mm. For kids, the number is generally from 41 to 55mm. If your number is outside this range, you may have made a mistake. Please do not guess or assume your PD.