Evacuation of an air conditioner, heat pump, or any refrigeration system is critical for proper performance and longevity. On a new installation of an air conditioner or heat pump, the outdoor unit is sealed at the factory so the tubing and indoor coil must be evacuated. Most refrigeration systems and larger air conditioners come charged with dry nitrogen, so that must be removed prior to evacuation and at that point we will be evacuating the outdoor unit also.
To do a proper evacuation, a few things are needed:
Now with the proper equipment connected, open the gauges and start the vacuum pump. Let the pump run until you get to 1000 microns, then isolate the pump and watch and wait if it holds 1000 microns for at least 10 minutes. Then you know you have no leaks.
If it doesn’t hold then you either have a leak or moisture in the system. Turn the pump back on, open the gauges and pull it back down to 1000 microns and wait 10 minutes. If it holds this time then the problem was moisture; if it still doesn’t hold, find and repair your leak, then start over.
If it does hold, start the pump and open the gauges until you are pulled down to 500 microns. At that point it should hold and you can start charging the system.
Now if your equipment isn’t up to snuff, you can do what is called a triple evacuation. If your pump will not pull down to microns, evacuate as low as possible and leak check in a vacuum, then break the vacuum with dry nitrogen until you get above 2 psi in the system, then wait approximately one hour then remove the dry nitrogen and repeat the above steps three times then you can start charging the system.
Triple evacuation can be done even if your equipment pulls down to microns, the difference is in the waiting time between pump downs. Pulling into microns doesn’t require a one hour wait time between pump downs.
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