How to Properly Evacuate an AC or Heat Pump

  August 11, 2020      Jeff Rosenblum


Well, the warm weather is here, and with that comes an increase in AC installs. I wanted to take a moment to discuss the right way to evacuate a system. Keep in mind, the right way has nothing to do with time. It has to do with what level vacuum we achieved and if that level held when isolated.

To start off, you must have the correct tools for the job. Without these, you can not properly perform the task at hand. See below:

  • Vacuum pump with extra oil
  • Micron gauge
  • Evacuation hose and vacuum rated core puller (optional)
If you do not have these, STOP! Do not proceed until you are properly equipped. I'll wait... 

Now that everyone has the tools needed, let’s get started! I'll discuss the method using the evacuation hose and core puller.

  1. Connect the core puller to the liquid line service port and remove the core.
  2. Connect the hose to the core puller and the larger end to the vacuum pump.
  3. Connect the micron gauge to the suction service port.
  4. Turn the micron gauge on and start the pump. Allow the pump to run, and make sure to keep an eye on the micron gauge. Our target is 500 microns or lower. 
    NOTE: Most manufacturers recommend a level of below 500 microns.

Removing the "air" is easy (usually done by 5000 microns). Dehydrating the system is a bit more difficult and requires a deeper vacuum. So how are we actually removing moisture? Well, as we pull a deeper vacuum we also reduce the boiling point of water. By pulling a deep vacuum, we get the moisture in the air to boil off at ambient temperature.

Once we have achieved the correct micron level, isolate the pump from the system by closing off the valve on the pump or by closing the valve on the core puller. Now we wait. I usually recommend waiting around 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 sometimes have a different threshold.

I always get asked "how long will it take?" The answer is, "who knows?" It may take 5 minutes. It may take all afternoon. It’s hard to tell, but having fresh oil in a properly functioning vacuum pump will help speed things along.

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