VACUUM

As has been stressed above, refrigerant is sensitive to moisture in the system. To understand how water behaves and how to dry out a system, the following natural law must be understood. The boiling point of water varies depending on pressure. In SI unites, pressure are expressed in KPa (Kilopascals). Normal atmospheic pressure is 101.3KPa. But for practical engineering purposes, gauges are often calibrated at 100 KPa for atmospheric pressure. Pressures lower than atmospheric are called partial vacum. Zero on the absolute presser scale is at a pressure which cannot be further reduced. A perfect vacuum is 0 Pa.(Pascal"s) The pascal, rether than the kilo pascal, is used for measuring high vacuums (pressures close to an absolute vacuum). The relationship between absolute and guage pressre is also impornt to understand when preforming a vacuum procedure on your system. Gauges are normally calibrated to read zero at the atmospheric pressure but not always. In this illustration the atmospheric pressure is assumed to stanrd at sea level.

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