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How to evacuate AC | DoItYourself.com

Evacuation of an air conditioner is necessary after repairs that require the sealed components to be opened. Sealing means that moist air can infiltrate the system and that moisture must be removed in order for efficient cooling to continue. The following description guides you through the processes required to properly evacuate your air conditioning system.

Why evacuate?

Air conditioning systems are evacuated to remove all air and / or moisture from the system components. This guarantees the best possible conditions for maximum cooling efficiency without freezing. Moisture in the system will freeze and likely block the flow of refrigerant, which can cause excessive pressure conditions and possibly damage AC system components. Air in the system reduces the ability of the air conditioner to cool efficiently.

Each time an air conditioning system is opened for exposure to air, it must be evacuated to ensure the best performance. The air conditioning desiccant (desiccant) contained in the receiver / dryer collects quite a lot of moisture when opened and exposed to air. This moisture will take some time to boil away under vacuum. The desiccant will remove and trap a lot of moisture from the refrigerant and will work well if it is completely dried by vacuuming before the refrigerant is charged.

A coolant cleaner will remove air from the system, but it does not remove moisture from the desiccant, hence the need to use vacuuming for an extended period of time.

manifold meter set


Air conditioning systems are evacuated by placing the connected components under vacuum. Most vacuum pumps do not achieve a full vacuum of 29.6 “Hg, but only handle 20-25” Hg. The smaller vacuum achieved with your pump dictates the longer vacuuming times to achieve the desired result. When the desired vacuum range has been reached, you can switch off the vacuum pump and close the measuring valves for several minutes.

Check the vacuum reading when the valves are closed and check again in 30 minutes. If the vacuum reading increases more than 2 ”/ Hg on the meter, check for leaks and repair if necessary. The system must be able to hold vacuum for at least 30 minutes, or when charged with refrigerant, the refrigerant will escape and the air conditioner will not work.

You will need a coolant manifold kit, a vacuum pump and a set of basic hand tools. Some skills and knowledge are also necessary for the safe and correct use of refrigeration equipment. Examining and reading how to use manuals will help you use the tools safely and efficiently.

vacuum air pump for evacuating air conditioner


Connect all hoses and components in auto air conditioners, install manifold gauge by connecting the yellow hose to the vacuum pump. Connect the blue hose to the suction side service port on your air conditioning system (larger hose) and the red hose to the pressure side service port (smaller hose).

Open all valves and switch on the vacuum pump. When vacuum is reached, close all valves and turn off the pump. Note the reading on the vacuum gauge and check again in 10 minutes. If there is no change, turn on the vacuum pump and open all valves to resume vacuuming. If the vacuum gauge has changed reading, find and repair any leaks.

to evacuate outdoor AC unit

When the leak is repaired, start the vacuuming process again. Continue vacuuming for at least one hour and even longer in conditions of high humidity or if your vacuum pump will not achieve a good vacuum in excess of 20 ”Hg. You want to suck out all the moisture as possible.

The trapped moisture slowly boils away, which is the need for prolonged vacuuming. When the air conditioning system will hold vacuum for 30 minutes with all valves closed and the vacuum pump turned off, it is ready for charging with coolant.

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