Refrigeration Maintenance
112
Unit Evacuation
NOTE: The electrical system must be energized
throughout this procedure.
1. To prepare the unit for evacuation, recover
any refrigerant to 0 psi (0 kPa). (New Federal
Regulations may require your recovery
machine to pull the system’s pressures lower
then 0 psi [0 kPa]).
2. Close the isolation valve at the thermistor to
isolate the vacuum gauge. Turn the vacuum
gauge on to warm it up.
3. Open the compressor service valves and the
receiver outlet valve.
4. Replace and tighten the valve stem caps on all
three service valves.
5. Open the vacuum valve at the vacuum pump
and start the pump.
6. After evacuating the system for 5 minutes,
open the isolation valve at the thermistor to
access the vacuum gauge.
7. Evacuate the system to 500 microns. Back
seat the suction service valve and then
continue to evacuate the system for one
additional hour.
NOTE: The presence of refrigerant in the
compressor oil may prevent a low micron
reading from being achieved. The oil can
continue to “outgas” for long periods of
time. If the micron level appears to stall after
1/2 hour or 45 minutes between 1000 and
1500 microns, back seat the suction service
valve and observe the micron gauge. A sharp
drop in the micron reading (300 to 500
microns) indicates that refrigerant is in the
oil or a leak exists in the compressor area.
8. After the hour of additional evacuation time,
open the suction service valve. The vacuum
gauge reading will rise. Continue to evacuate
the system back down to 500 microns. When
the system reaches 500 microns, back seat the
suction service valve, close the vacuum valve
at the vacuum pump, and stop the pump.
9. Observe the reading on the vacuum gauge for
5 minutes. The pressure should not exceed
2000 microns. If the pressure exceeds 2000
microns in 5 minutes, a leak is present, or
additional evacuation time is required.
10. If the vacuum level is acceptable, start the
pump and open the vacuum valve. Evacuate
the system for 5 minutes to remove the
pressure rise. Close the vacuum valve and stop
the pump. Observe the vacuum gauge to
confirm that the system remains in a deep
vacuum.
11. Close the isolation valve at the thermistor. The
unit is now ready to charge.
CAUTION: Do not attempt to evacuate a
unit until you are sure that the unit is leak
free. A unit with less than a full
refrigerant charge should be thoroughly
leak checked and all leaks must be
repaired.
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