Auto A/C Terms - Glossary
Vacuum Pump

One of the most critical pieces of shop equipment required when servicing any auto A/C system. Vacuum pumps are nothing more than a mechanical device used to evacuate or remove all the air in an A/C system.

Air creates a number of problems for automotive air conditioning systems. First of all, air has moisture. That moisture, when mixed with refrigerants (freon) will react to form harmful acids in the system. Those acids will corrode A/C components like condensers and evaporators, causing them to leak prematurely.

Secondly, air is a non-condensable gas. That means when found in the A/C system, it will create excessive high side pressure gauge readings and limit the cooling performance. Air in the A/C system is one of the most difficult problems to diagnose.

Therefore, before recharging any auto A/C system, the complete system must be vacuumed. The level of vacuum attained is also important. When measured in microns, (unlike inches of vacuum, microns are millionths of a millimeter and far more accurate when measuring vacuum) water boils at levels of vacuum under 1,500 microns. The A/C system requires deep vacuum which is a level below 500 microns.

It’s also important to remember that water (moisture) will boil in a vacuum. Therefore, it is important to attain deep vacuum to assure that any moisture that may be in the A/C system is boiled off and removed.

In order to attain vacuum, the vacuum pump must be connected to the A/C system through the manifold pressure gauges set. Operating a good, properly operating vacuum pump for a minimum of 1/2 should remove the air and moisture from the system, preparing it for recharging.