Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

Page: 132 / 162

3. Operate the vacuum pump to evacuate the system to the best attainable vacuum. The
vacuum must be less than 500 μm, but if that cannot be attained, a vacuum at 1000 μm or
lower is acceptable.
4. To start the 8 hour vacuum hold test, close the system charging valve connection to the
vacuum pump. Note the time and pressure.
5. Hold the vacuum obtained in Step 4 in the system for 8 hours. Any rise that exceeds the limits
in Step 7 can indicate a leak, the presence of moisture, or both. It is important to check for
pressure change with the chiller at the same temperature. Pressure changes proportional to
temperature and affects results.
6. To determine if it is moisture or a leak, conduct a pressure rise test. Evacuate the system to
5,000 μm again and perform another hold test.
- If the pressure rise goes to 0 psig, it indicates that a leak is present.
- During the hold period, if moisture is present, the pressure stabilizes at some level
below atmosphere and should correspond to the room ambient temperature or the
heat being applied to the vessel. See Table 94 for values.
7. An acceptable vacuum pressure rise is 150 μm in 60 minutes.
- 1000TR 1,000 μm
- See factory standard
8. If the vacuum does not hold within the limits defined in Step 7, you must find and repair the
leak. For cases where leaks cannot be identified while pressurized but vacuum hold tests
indicate that there is a leak, in most cases this can be traced to an elastomeric or O-ring
sealing issue.
Result
When the 500 μm hold test is successful, you can charge the system using the steps in Refrigerant
charging .
Refrigerant charging
Before beginning, it is critical to establish that the vapor portion of the refrigerant container or
cylinder has not been contaminated with other gases that are not R-134a, including air. Use the
appropriate saturation property R-134a. See Table 95 to determine if the saturation pressure and
ambient temperature of the refrigerant in the container indicates that the gas pressure coincides
with the corresponding temperature.
To prevent liquid freezing within any of the chiller tubes when charging an evacuated system, make
sure that only the refrigerant vapor from the top of the drum or cylinder is admitted to the system
until the system pressure is raised above the corresponding saturation pressure at the freezing
point of the chilled liquids. For all other liquids, establish the freeze point temperature and vapor
charge to an appropriate pressure that is 5°F (2.78°C) higher than that freeze point. For water with
R-134a at 32°F, that pressure is 28 psig. See Table 95.
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