MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 3: Refrigeration Basics and Service
2-3
March 2013
Page 48
Proprietary/Confidential
© 2013 Twist, Inc.
To determine if sufficient charge has been introduced, close the
refrigerant cylinder valve and observe the system operation. Continue
charging until the proper charge has been added. Again weigh the
refrigerant drum and subtract the previously determined weight to
ensure that only the proper amount of refrigerant has been added.
At times the sight glass may show bubbles or flash gas even when the
system is fully charged. A restriction in the liquid line ahead of the sight
glass may cause a sufficient pressure drop to cause flashing of the
refrigerant. If the expansion valve feed is erratic or surging, the
increased flow when the expansion valve is wide open can create a
sufficient pressure drop to create flashing at the receiver outlet. Rapid
fluctuations in condensing pressure can also be a source of flashing.
While the sight glass is a valuable aid in determining the proper charge,
the system performance must be carefully analyzed before placing full
reliance on it as a positive indicator of the system charge.
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