Manitowoc J-1300, Руководство по обслуживанию

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Section 7 Refrigeration System
7-13
SAFETY LIMITS
General
In addition to standard safety controls, such as high
pressure cut-out, the control board has four built in
safety limit controls which protect the ice machine
from major component failures. New style control
boards have two safety limit controls.
Safety Limit #1: If the freeze time reaches 60
minutes, the control board automatically initiates a
harvest cycle. If three consecutive 60-minute freeze
cycles occur, the ice machine stops.
Safety Limit #2: If the harvest time reaches 3.5
minutes, the control board automatically returns the
ice machine to the freeze cycle. If three consecutive
3.5 minute harvest cycles occur, the ice machine
stops.
Safety Limit #3: if the compressor discharge line
temperature falls below 85
°
F/29.4C for three
consecutive harvest cycles, the ice machine stops.
Safety limit #4: If the compressor discharge line
temperature reaches 255
°
F/123.8
°
C for 15 continuos
seconds during a freeze or harvest cycle the ice
machine stops.
Determining which safety limit stopped the ice
machine
When a safety limit condition causes the ice machine
to stop, the harvest light on the control board
continually flashes on and off. Use the following
procedures to determine which safety limit has
stopped the ice machine.
Step 1 Move the toggle switch to off.
Step 2 Move the toggle switch back to ice.
Step 3 Watch the harvest light. It will flash one to
four times, corresponding to safety limits 1-4,
to indicate which safety limit stopped the ice
machine.
After safety limit indication, the ice machine will
restart and run until a safety limit is exceeded
again.
Analyzing Why Safety Limits
May Stop the Ice Machine
According to the refrigeration industry, a high
percentage of compressors fail as a result of external
causes. These can include: flooding or starving
expansion valves, dirty condensers, water loss to the
ice machine, etc. The safety limits protect the ice
machine (primarily the compressor) from external
failures by stopping ice machine operation before
major component damage occurs.
The safety limit system is similar to a high pressure
cut-out control. It stops the ice machine, but does not
tell what is wrong. The service technician must
analyze the system to determine what caused the high
pressure cut-out, or a particular safety limit, to stop
the ice machine.
The safety limits are designed to stop the ice machine
prior to major component failures, most often a minor
problem or something external to the ice machine.
This may be difficult to diagnose, as many external
problems occur intermittently.Example: An ice
machine stops intermittently on safety limit #1 (long
freeze times). The problem could be a low ambient
temperature at night, a water pressure drop, the water
is turned off one night a week, etc.
When a high pressure cut-out or a safety limit stops
the ice machine, they are doing what they are
supposed to do. That is, stopping the ice machine
before a major component failure occurs.
Refrigeration and electrical component failures may
also trip a safety limit. Eliminate all electrical
components and external causes first. If it appears
that the refrigeration system is causing the problem,
use Manitowoc’s Refrigeration System Operational
Analysis Table, along with detailed charts, checklists,
and other references to determine the cause.
The following checklists are designed to assist the
service technician in analysis. However, because
there are many possible external problems, do not
limit your diagnosis to only the items listed.