PUMP DOWN OF UNIT
To replace or repair refrigeration system components, it will be necessary to pump the refrigerant out of the evaporator
and tubing into the receiver tank of the condensing unit to replace an expansion valve and dehydrator. .To pump down
the unit, attach a compound pressure gage to the suction service valve. Close the receiver service valve and allow the
compressor to run until the pressure drops to 3 p.s.i. Start and stop unit several times to reach the 3 p.s.i. pressure
reading to prevent too fast a pumping effect which will cause excessive foaming of crankcase oil. When the 3 p.s.i.
pressure reading is indicated, turn in to close (clockwise) the suction service valve. The replacement parts can now be
After the necessary repairs have been done on the refrigeration system, non-condensible gas such as air has to be
removed from the lines and system parts. Air in the condenser will cause excessive high side pressure resulting in long
operating periods. To purge air from system, close the suction service valve and loosen the flare nut at the suction valve.
Open the receiver service valve slightly to permit Freon vapor to push the air through the system and out at the suction
service valve flare nut. The time to complete the purging will be approximately 30 seconds. When the purging is
complete, the suction service valve flare nut can be tightened.
Charge this system with refrigerant-12 only. The recommended method of charging refrigerant into a refrigerating system
of this type is to charge thru the low side (suction side) of the system. Extreme care must be observed so that raw liquid
does not enter the compressor and injure the valves. Charge with the refrigerant drum in an upright position only. Allow
the compressor to pump refrigerant vapor from the Freon drum being used for the charging operation. Connect a
conventional charging manifold with gauges attached to the suction service valve port and Freon drum. Start the
compressor and add a little gas at a time to prevent overcharging. To determine the required amount of Freon added to
the system, observe the noise level of the expansion valve when charging the system. A hissing noise in the valve
indicates a shortage of refrigerant. Add refrigerant until the hissing noise in expansion valve has been eliminated. Close
suction service valve port and remove charging hose.