Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

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is carried out through the vacuum pump and the temperature or pressure shown by the indicator
drops uniformly until it reaches a temperature of 35°F (1.6°C) or a pressure of 5,000 μm.
When the vacuum indicator registers this temperature or pressure, it is a positive sign that the
system is dehydrated to the recommended limit. If this level cannot be reached, it indicates that
there is a leak somewhere in the system. Any leaks must be corrected before you can evacuate the
system to 35°F (1.6°C) or 5,000 μm. During the primary or dehydration evacuation, closely monitor
the vacuum level. Do not let it fall below 5,000 μm or the equivalent 35°F (1.6°C).
If the pressure temperature relationship falls to 32°F (0°C), the water in the system freezes, and
the result is a faulty pressure reading. Use the following procedure as a guide to the steps for
dehydration.
Conducting the dehydration process
1. Connect a high-capacity vacuum pump, with indicator, to the three system vapor charging
valves as shown in Figure 50 and start the pump.
2. Fully open all the system valves. Make sure that all valves to the atmosphere are closed with
flare caps in place if applicable.
3. Operate the vacuum pump until a pressure of 5,000 μm is reached. To avoid freezing any
trapped moisture in the system, see Table 94 for corresponding pressure and temperature
values.
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. Even a slight rise in pressure
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 can affect 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 for the first 60 minutes.
8. If the vacuum does not hold for within the limits defined in Step 6, 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 5,000 μm vacuum hold test is successful, you can perform a final evacuation.
Conducting the final evacuation
About this task:
After the pressure test and vessel dehydration have been completed, conduct the final evacuation
as follows:
1. Connect a high capacity vacuum pump, with indicator, to the system charging valve as shown
in Figure 50.
2. Fully open all the system valves. Make sure that all valves to the atmosphere are closed with
flare caps in place if applicable.
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