Between "pressure and evaporation temperature of water, the vacuum of 28" the evaporation temperature will be 38 ° C. Since all common compressors reach a maximum of 28 "vacuum, it is concluded that a common compressor can not be used as a vacuum pump because there is no evaporation of water.
To ensure that water evaporates throughout the system, it is necessary to reach a minimum of 250 microns, corresponding to an evaporation temperature of -31 ° C, for which it is necessary to use a high vacuum pump .
Vacuum is required on both the high pressure side and the low pressure side. As measurements are not made at the farthest points, a high vacuum is required to ensure that a satisfactory vacuum has been achieved throughout the system.
In refrigeration installations the value of 500 microns is adopted, to guarantee that we will have a good vacuum, without air (oxygen and nitrogen) and humidity.
For a perfect evacuation of the system, it is necessary to break the vacuum, at least three times, with nitrogen or by the own refrigerant to be used, thus allowing moisture to drag from the most distant parts.
The duration of an evacuation depends only on the size of the installation and the capacity of the vacuum pump.