Operational Analysis (Diagnostics) General - Manitowoc J250 Service Manual

Refrigeration System
Operational Analysis (Diagnostics)
GENERAL
When analyzing the refrigeration system, it is
important to understand that different refrigeration
component malfunctions may cause very similar
symptoms.
Also, many external factors can make good
refrigeration components appear bad. These factors
can include improper installation, or water system
malfunctions such as hot incoming water supply or
water loss.
The following two examples illustrate how similar
symptoms can result in a misdiagnosis.
1. An expansion valve bulb that is not securely
fastened to the suction line and/or not insulated
will cause a good expansion valve to flood. If a
service technician fails to check for proper
expansion valve bulb mounting, he may replace
the expansion valve in error.
The ice machine now functions normally. The
technician erroneously thinks that the problem
was properly diagnosed and corrected by
replacing the expansion valve. Actually, the
problem (loose bulb) was corrected when the
technician properly mounted the bulb of the
replacement expansion valve.
The service technician's failure to check the
expansion valve bulb for proper mounting (an
external check) resulted in a misdiagnosis and the
needless replacement of a good expansion valve.
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2. An ice machine that is low on charge may cause a
good expansion valve to starve. If a service
technician fails to verify the system charge, he
may replace the expansion valve in error.
During the replacement procedure, recovery,
evacuation and recharging are performed
correctly. The ice machine now functions
normally. The technician erroneously thinks that
the problem was properly diagnosed and
corrected by replacing the expansion valve.
The service technician's failure to check the ice
machine for a low charge condition resulted in a
misdiagnosis and the needless replacement of a
good expansion valve.
When analyzing the refrigeration system, use a
Refrigeration System Operational Analysis Table.
This table, along with detailed checklists and
references, will help prevent replacing good
refrigeration components due to external problems.
Section 7