Testing - Scotsman MAR1400 User Manual

Testing

COMPLETE SYSTEM LEAK TESTS
During pressure testing for leaks, keep the
compressor suction service valve and discharge
service valve closed to prevent air and moisture
from entering the compressor. All other valves in
the system must be open. Add just enough liquid
refrigerant R-22 to the system to raise the
pressure slightly, then add dry nitrogen to obtain
the desired test pressure (11 atm or 170 PSIG is
sufficient).
Leak testing shall be performed with an electronic
leak detector. Refrigeration piping will not be
acceptable unless it is gas tight.
If any leaks are found, isolate the defective area,
discharge the gas and repair the leaks and then
repeat the test. When testing has been completed
release all pressure freely to atmosphere.
COMPLETE SYSTEM EVACUATION
Use a vacuum pump that has a capacity of pulling
a vacuum of 50 microns or less.
Evacuation of the system must never be done by
the use of the refrigerant compressor. The vacuum
pump should be connected to both the low and
high side evacuation valves with vacuum hoses.
The hand valves should remain closed to isolate
the new part of the system from the rack. A high
vacuum gauge capable of registering pressure in
microns should be attached to the system.
Evacuate the system to 300 microns.
CHARGING: DEDICATED SYSTEM
When a dedicated condensing unit (a condensing
unit that is only used by the MAR flaker) is used,
charge the system through the fitting in the liquid
line. Weigh the refrigerant drum before charging so
that an accurate record can be kept of the weight
of refrigerant put in the system. If refrigerant is
added to the system through the suction side on
the compressor, charge in vapor form only. Charge
the system until the sight glass in the liquid line
shows a clear flow of liquid refrigerant.
Bubbles or foam usually indicate insufficient
refrigerant, even if there could be other reason for
the bubbles or foam to appear in the sight glass.
So, the practice to relay on the sight glass only to
determine whether the systems is correctly
charged is certainly good but not fully positive.
After the final leak test, refrigerant lines exposed
high ambient conditions should be insulated to
reduce heat pick-up and prevent the formation of
flash gas in the liquid lines.
Suction line should be insulated if exposed, to
prevent condensation.
CHARGING: RACK SYSTEM
Open the liquid and suction line valves.
December 2000
Page 17
MAR1400 & MAR2000