Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

Page: 128 / 162

c. If a leak is present, the pressure pushes the cork out of the tube. If this occurs, the tube
must be plugged or have other options explored.
d. If a tube or tubesheet leak is confirmed, contact product technical support (PTS) for
guidance on repair procedures.
10. When all leaks have been identified, recover the test gas as applicable, make the necessary
repairs, repeat the leak tests, evacuate the chiller, and perform the time-based pressure hold
test.
System evacuation
WARNING
Ensure that power is removed from the input side of the variable speed drive at all times when the
chiller is under vacuum (less than atmospheric pressure). The variable speed drive maintains voltage
to ground on the motor when the chiller is off while voltage is available to the variable speed drive.
Insulating properties in the motor are reduced in vacuum and may not insulate this voltage sufficiently.
Vacuum dehydration
Before you perform the final evacuation and system charging, it is necessary to obtain a sufficiently
dry system. The following instructions have been assembled to provide an effective method
for evacuating and dehydrating a system in the field. Although there are several methods of
dehydrating a system, the following method produces one of the best results and provides
accurate readings of the extent of dehydration. The equipment required to follow this method of
dehydration consists of the following items:
• High resolution vacuum gauge (microns below 500)
• Chart that shows the relationship between dew point temperature and pressure in microns
(vacuum), see Table 94
• Vacuum pump that can pump a suitable vacuum on the system
Follow the dehydration steps as closely as possible to prevent moisture from becoming trapped
in the system. If you apply too deep of a vacuum, any trapped moisture might freeze and not be
exhausted as vapor. Failure to remove all of the moisture can create acids in the refrigerant circuit.
These acids can damage internal system components over time and cause premature failure of
items such as the compressor, motor, and any other devices sensitive to acid contact.
YVAM Control Center 128