Manitowoc Q450 Service Technician's Handbook page 171

Dry nitrogen is recommended for this procedure.
This will prevent CFC release.
10. Follow the normal evacuation procedure, except
replace the evacuation step with the following:
A. Pull vacuum to 1000 microns. Break the
vacuum with dry nitrogen and sweep the
system. Pressurize to a minimum of 5 psig
(35 kPa).
B. Change the vacuum pump oil.
C. Pull vacuum to 500 microns. Break the vacuum
with dry nitrogen and sweep the system.
Pressurize to a minimum of 5 psig (35 kPa).
D. Change the vacuum pump oil.
E. Pull vacuum to 250 microns. Run the vacuum
pump for 1/2 hour on self-contained models, 1
hour on remotes.
NOTE: You may perform a standing vacuum test to
make a preliminary leak check. You should use an
electronic leak detector after system charging to be
sure there are no leaks.
11. Charge the system with the proper refrigerant to the
nameplate charge.
12. Operate the ice machine for one hour. Then, check
the pressure drop across the suction line filter-drier.
A. If the pressure drop is less than 1 psig, the
filter-drier should be adequate for complete
cleanup.
B. If the pressure drop exceeds 1 psig (7 kPa),
change the suction line filter-drier and the liquid
line drier. Repeat until the pressure drop is
acceptable.
13. Operate the ice machine for 48-72 hours. Then
remove the suction line drier and change the liquid
line drier.
14. Follow normal evacuation procedures.
Important
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