14-17. AIR-CONDITIONING SYSTEM SERVICING (R-12) (Cont'd)
e. Evacuating System
Never attempt to evacuate A/C system if system has not been
Discharge A/C system (refer to task c.) and flush A/C system if necessary (refer to task d.).
Connect manifold gauge set (refer to task a.).
Turn each service valve shaft (5) clockwise to mid-seated position.
Connect vacuum pump to center hose (4) on manifold gauge set (3).
Turn vacuum pump on and open low pressure gauge valve (1) and high pressure gauge valve (2) on
manifold gauge set (3).
High side gauge should drop to "zero" or below. If not, a blockage
in A/C system is indicated.
29-30 pounds of vacuum should be sustained on low pressure
gauge for at least ten minutes. If not, a leak in A/C system is
indicated. Identify source of leak and repair as necessary.
Evacuate unit until low pressure gauge reads 29-30 pounds vacuum.
Continue evacuation for forty-five minutes after correct gauge reading of 29-30 pounds vacuum has
Turn low pressure gauge valve (1) and high pressure gauge valve (2) on manifold gauge set (3) to
closed position after evacuation is complete.
Turn off vacuum pump and disconnect center hose (4) from vacuum pump.
Turn service valve shafts (5) to "back-seated" position.
Manifold gauge set can remain connected and service valves left
in mid-position. If charging A/C system will follow immediately.
Disconnect manifold gauge set (refer to task b.).