Section 7 | Refrigeration System |
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SAFETY LIMITS
General
In addition to standard safety controls, such as high pressure
Safety Limit #1: If the freeze time reaches 60 minutes, the control board automatically initiates a harvest cycle. If 6 consecutive
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
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.
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