Properly Evacuating ACs & Heat Pumps

  July 1, 2017      Jeff Rosenblum


Warm weather is fast approaching, and with that comes an increase in air conditioner installs. This brings up an important topic: correctly evacuating a system. The right way has nothing to do with time; it’s about the level vacuum achieved and if that level held when isolated.

Be sure to have the tools listed below for the job otherwise the task cannot be properly performed. Do NOT proceed until you are properly equipped.

  • Vacuum pump with extra oil
  • Micron gauge
  • Evacuation hose and vacuum rated core puller (optional)

First we’ll use the evacuation hose and core puller. Connect the core puller to the liquid line service port and remove the core. Next, connect the hose to the core puller and the larger end to the vacuum pump. Then connect the micron gauge to the suction service port. Lastly, turn the micron gauge on and start the pump. Allow the pump to run while keeping an eye on the micron gauge. Most manufacturers recommend a level below 500 microns.

Removing the “air” is easy and is usually done by 5000 microns. Dehydrating the system is a bit more di cult and requires a deep vacuum. How are we actually removing moisture? As we pull a deep vacuum we reduce the boiling point of water, which allows the moisture in the air to boil o at ambient temperature.

Once we’ve achieved the correct micron level, isolate the pump from the system by closing o the valve on the pump or by closing the valve on the core puller. Wait about 30 minutes. If it holds vacuum without going over the 500-micron mark, the system is sealed and properly dehydrated. You may need to pull below 500 microns to get it to hold at 500 when isolated. This method is good for most residential systems. Commercial, industrial, and refrigeration systems may have a different goal.

It’s hard to say exactly how long it will take. Having fresh oil in a properly functioning vacuum pump will help speed things along. If you need technical assistance please call the Famous Supply Tech Support Team.

Jeff Rosenblum 
Technical Support
18 Years Industry Experience
Cell (330) 962-2491
[email protected]