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Every A/C system must be vacuumed before recharging. Creating a vacuum on the A/C system assures that there is no air left in the system before charging with refrigerant (freon).

This is a very important part of auto A/C service. Simple mistakes made when pulling a vacuum can cause problems with the cooling performance of any A/C system because air would be left in the system. Air is known to be a noncondensible. That means it will typically remain at the condenser inlet and create pressure gauge readings that are higher than normal. Those higher pressure gauge readings will mean that the refrigerant is not getting cooled enough to work efficiently.

In addition to that, not only is vacuum important, but the level of vacuum attained is just as important. Consider that water boils in a vacuum when the level of vacuum drops below 1,500 microns. Deep vacuum is considered to be levels of vacuum under 750 microns, and you should really be aiming to attain 500 microns or less for at least 1/2 hour.

Removing the moisture from the A/C system will assure that water droplets will not freeze inside the A/C system and cause restrictions in flow. Additionally, it’s important to understand that moisture left in the system will mix with the refrigerant and create acids that are very harmful to the A/C system’s components. When those acids form, they begin to corrode the A/C system’s components causing them to leak.

Whenever performing a vacuum, be sure that the vacuum pump is working to maximum performance. You can only assure the performance of the vacuum pump using a micron vacuum gauge. For the best performance from your vacuum pump, you should be sure that the vacuum pump is maintained properly and that the vacuum pump oil is changed at least every 15-20 hours of operation.

Vacuum pump service kits to restore deep vacuum to your vacuum pump

Also see What vacuum pump manufacturers don't want you to know!

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