Safety Limits - Manitowoc MARINE MODEL S1800 Service Manual

Section 7

SAFETY LIMITS

General
In addition to standard safety controls, such as high
pressure cut-out, the control board has two built in safety
limit controls which protect the ice machine from major
component failures.
Safety Limit #1: If the freeze time reaches 60 minutes,
the control board automatically initiates a harvest cycle.
If 6 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 500 consecutive 3.5 minute harvest cycles occur, the
ice machine stops.
Safety Limit Indication
When a safety limit condition is exceeded:
• Six consecutive cycles for safety limit 1 - the
control board enters the limit into memory.
• Three consecutive cycles for safety limit 2 - the
control board enters the limit into memory and
the ice machine continues to run.
Use the following procedures to determine if the control
board contains a safety limit indication.
1. Move the toggle switch to OFF.
2. Move the toggle switch back to ICE.
3. Watch the safety limit lights (SL-1 and SL-2). If a
safety limit has been recorded, either the SL-1 light
will flash once or the SL-2 light will flash twice,
corresponding to safety limit 1 or 2 to indicate which
safety limit stopped the ice machine.
Part Number 80-1634-3
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.
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.
Refrigeration System
7-9