Bubba Moore

Technical Services Manager Southeast District

Deep Vacuum Method Chart

How do you know the system has been adequately evacuated? First, the system needs to be vacuumed to 500 microns or below, then it is isolated from the vacuum pump. Now the vacuum gauge needs to be monitored to see if there are any changes in the level of vacuum in the system. If the vacuum gauge shows a pressure rise and the pressure continues to rise without leveling off, a leak exists somewhere and needs to be located and repaired.

If the vacuum gauge shows a pressure rise and levels off between1,000 and 2,000 microns within seven minutes, the system is leak free but still too wet. A constant reading on the vacuum gauge of 500 to a 1,000 microns within seven minutes indicates a tight leak free dry system.

The Triple Vacuum Method

The triple evacuation method can take about three hours when performed as recommended. The system is first evacuated to 5,000 microns during the first and second evacuations. Between the evacuations, the system is pressurized with dry nitrogen to about 10 psig and allowed to sit for an hour so the nitrogen can absorb the moisture. For the third and last evacuation, a deep vacuum of 500 microns is preformed and the system is monitored in the same manner described for the deep vacuum method.

Triple Vacuum Method Flow Chart - HVAC Evacuation

The deep vacuum and triple vacuum methods are both used frequently to evacuate and dehydrate refrigeration systems. The deep vacuum method is normally used when new equipment is installed or the refrigeration system was opened for a repair. The triple vacuum method is usually done and recommended, if the system is especially wet or after contaminants are found in the refrigerant system.

These evacuation procedures help protect and can extend the life of a system.