How to Evacuate an Air Conditioning System (Fast and Deep Vacuum)

In this video, we demonstrate how to evacuate an air conditioning system with a fast and deep vacuum. As usual, we cover some of the best evacuation practices along the way. Bryan uses the BluVac app to display data throughout the evacuation process.

Evacuation refers to when we pull the inside of the A/C circuit into a vacuum. Under vacuum conditions, the water would boil at a lower temperature due to the removal of atmospheric pressure (14.7 PSIA). Evacuation essentially sucks the air and gaseous contaminants out of an A/C system’s refrigerant circuit. Liquid water, however, can’t be sucked out of a system; it must be boiled out.

Before evacuation, we want to make sure that the suction pressure stays relatively constant over the span of several minutes.

We use core removal tools (CRTs) when we do our evacuations. These tools allow us to insert or remove Schrader cores when the valve is in the open position. We simply attach the CRT to the refrigerant line in the closed position, tighten it down, open the valve, push the core to unscrew and remove it, close the valve, and remove the section that contains the core.

Removing the cores during evacuation allows us to get faster evacuations when we connect our hoses to the CRT. Schrader cores provide a restriction, and we can speed up our evacuations by removing that restriction with a good CRT. We also recommend attaching the micron gauge to the CRT’s side port.

After seeing that our suction pressure has held steady, we can pull the vacuum. Bryan attaches the CRTs on both sides with the vacuum-rated hoses and micron gauge. We don’t pull the vacuum through the gauges; we use hoses and pull through the CRTs. We keep the hoses sealed up until we need them so that we reduce the risk of contamination.

When we start up the vacuum pump, we notice that the dehydration period is short and that the vacuum pulls down very quickly. We are using the BluVac app, which allows us to see the saturation temperature of water under the pressure conditions, which is extremely low (-13 degrees Fahrenheit vs, the usual 212 degrees Fahrenheit). We pull down to 300 microns, which is what we recommend. When we reach that target, we valve off the CRTs and do our decay test.

Our vacuum rig consists of two large (1/2″) hoses in a T formation with a 3/8″ connector down to a 1/2″ connector. The connector is 1/4″ at the CRT.

The decay rate is the rate at which the pressure rises after pulling down a vacuum. The BluVac app can determine that our decay rate is well within an acceptable range within a few minutes, but many traditional decay tests last longer.

The BluVac app displays the maximum decay target and your decay target on the same graph; you can configure the app to suit your testing procedures and set your targets to make sure the app shows the data you need.

Read all the tech tips, take the quizzes, and find our handy calculators at