How to Vacuum an Automotive A/C

When a mobile A/C system  needs to be repaired, the first step taken is usually to recover the refrigerant from the system for reuse later.  An A/C vacuum pump is used to remove unwanted air and water vapor when it is under service.   Moisture and air in the system can potentially damage the system.  Air and moisture are harmful to an A/C system, because they react with refrigerant, and create an acid that can corrode the system  or destroy seals and o-rings.  In addition,  water condensation can cause the A/C system to freeze.

A vacuum should be pulled before refrigerant is added to the system, but after all the components have been replaced and the system has been sealed  Regular using a vacuum pump to create a vacuum which is deep enough to boil away residual  moisture is an excellent way to maintain the health of your A/C system.

What you’ll need:


Check oil level, Oil level in sight glass should be even with “oil level full” marks on each side of sight glass on front of vacuum pump. If oil level is low, add oil until oil level reaches full oil level marks. (see photo)

  • Make sure vacuum pump electrical switch is turned off. (see photo)
  • Plug electrical plug into a grounded 115 volt electrical outlet.
  • Connect yellow hose from manifold gauge set to inlet of vacuum pump. Make sure pressure in system is less than 5 psi. If pressure is over 5 psi vacuum pump may be damaged.
  • Turn switch to on. (see photo)
  • Vapor from exhaust port is normal during operation. This is the result of moisture in A/C system and humidity in shop.
  • Allow pump to operate until desired vacuum is reached.
  • Close manifold gauge set valves.
  • Turn switch to off position,
  • Disconnect yellow hose from vacuum pump,
  • Remove electrical plug from outlet. Grasp plug and pull from outlet. Pulling wire to disconnect plug from outlet will damage electrical plug

Maintain your Vacuum Pump

  • Check oil level through oil sight glass before each use. The main cause of vacuum pump failure is low oil levels and contaminated oil.
  • Always disconnect vacuum pump from electrical source before performing any maintenance,
  • Replace vacuum pump oil every week during heavy usage periods or after every service of a system with excess moisture.
  • Keep vacuum pump in a clean dry place.
  • Use FJC vacuum pump oil Part ft 2200 or equivalent.
  • Check electrical cord and plug for wear or damage each week. If damage or excessive wear is found, have cord replaced by a licensed electrical technician.

LMK 2020