When your Manitowoc ice machine shuts down prematurely, it most likely is going off on what’s called a safety limit. On Q Series ice machines there are 2 different safety limits, that will help you diagnose the problem. To check the which safety limit is the problem, simply turn your machine from the off position to ice and count how many times the harvest light flashes. Below are what the 2 safety limits mean.
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Safety Limit #1 : If the freeze time reaches 60 minutes, the control board automatically initiates a harvest cycle. If 3 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 #2 is a more common safety limit and can be caused by the ice maker simply being dirty. A dirty evaporator will hold ice and not allow it to fall until it is mostly melted away. Because there is not enough ice to force the water curtain open and break the bin switch, the machine simply thinks it never harvested.
Assuming your ice machine is clean, there are 2 other areas that are most common for shutting a Manitowoc Ice machine down on a safety limit #2. A missing magnet on the water curtain or your water curtain being broken will cause your bin switch to fail. The magnetic bin switch on a Manitowoc ice machine relies on proximity to the magnet to know when to terminate the harvest cycle. This switch will not read if it does not make proper contact with the magnet. To remedy this issue simply replace the water curtain.
Another culprit, which can also lead to intermittent problems, is a failed bin switch. The only way to properly test a magnetic bin switch is to OHM it out and look for consistency. However, it is possible for the switch to fail on say the 100th time, so if you are experiencing regular Safety Limit #2 lockouts, it might be a good idea to go ahead and eliminate the bin switch by replacing it.
Lastly, never underestimate a good cleaning. Most Manitowoc ice machine problems can be fixed without any parts, simply a good cleaning will return the ice maker back to proper operation. If you have any questions about diagnosing or replacing Manitowoc ice machine parts, ask your question below in the comment section.