Triple Evacuation vs. Deep Vacuum Method

  Little did I know, call it that HVAC Tech's ignorant moment, there are actually two different types of methods of evacuating a system free from non-condensables.  The Deep Vacuum and the Triple Evacuation methods are not one in the same.  Maybe my confusion started because I kind of used a hybrid to maximize my time on the job site.  Hopefully this could help you!
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  1. If the system indicates moisture, a multiple evacuation with a nitrogen sweep will significantly reduce the amount of moisture in the system. To preform this procedure, reduce the system pressure to between 1000 and 2500 microns. Isolate the vacuum pump with the core tools and disconnect the vacuum hose from the low side of the system. Break the system vacuum with nitrogen introduced at the side port of the core tool. Break the vacuum with nitrogen to that equivalent to atmospheric pressure (760,000 microns) then purge nitrogen through the system at 1-3 psig. from the high to the low side letting it vent out the open port of the core tool. Do not pressurize the system as this will not remove moisture. There is no need to pressurize the system unless you are performing a leak check. Increasing the system pressure will actually cause the water to drop out of the nitrogen similar to that of compressed air in an air compressor. Nitrogen does not absorb water, but entrains it and helps it move along out of the system, allowing the liquid water to warm, evaporate, and increase the water vapor pressure without introducing additional moisture into the system. If the system is drying out you will notice that deeper levels of vacuum are quickly achieved indicating progress in the job of dehydration. If desired or required repeat this process until the moisture is removed. Typically no more than a triple evacuation with sweep are required. If marked progress is not achieved during this process, repeat the nitrogen purge to remove liquid moisture that may exist. If a leak is indicated, it must be repaired before the evacuation can be completed.

  2. Thanks for this very detailed explanation! It's funny how you can have an understanding how a process can speed up your time on the job, but not completely understand what is happening. Like I had said, I was just a little too ignorant when it can to system evacuation over the years!

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