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HVAC School - For Techs, By Techs

Jan 12, 2017

n this episode, Bryan covers evacuation, recovery, and dehydration.

Evacuation refers to putting a vacuum pump on the system and pulling it down. We use a few different measures of vacuum, including inches of mercury ("Hg) or microns (millionths of a meter of mercury). We use such small units to measure a vacuum that effectively boils off moisture in the system. You must pull the vacuum very close to a perfect vacuum. So, a measurement of 500 microns indicates that the vacuum is 500 microns of mercury above a perfect vacuum.

Dehydration is a mere component (or result) of evacuation. If there is excess moisture in the system, it can freeze inside the system and cause blockages. It can also interact with oil and refrigerant inside the system to create an acid that ruins your unit.

To get a proper vacuum, you have to pull down to 500 microns. You can go lower than that, if possible, but 500 microns is the industry standard. Remember that Schrader cores restrict your vacuum. Remove them with a proper core remover tool for a more effective evacuation. Larger hoses and better equipment won't make a difference if you leave those Schrader cores in. If you don't have Schraders, you probably have a service valve.

Recovery removes refrigerant from a system under vacuum and puts it in a tank. We do recovery because we CANNOT vent refrigerant.

As a best practice, when you connect your vacuum rig to the port, you can use a little bit of Nylog thread sealant to keep moisture and other contaminants out.

Bryan also covers:

  • Push/pull method
  • Microns
  • Vacuum pump oil
  • Moisture contamination
  • Vacuum restrictions
  • Triple evacuation and sweeping nitrogen
  • King valves/service valves
  • De minimis

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