Diagnosing A Safety Limit

Manitowoc ice machines are programmed to shut down under situations that could potentially damage the machine, these are called Safety Limits.  Depending on the model of ice machine that you have, it could contain 2 to 4 different safety limits.  However, all safety limits can generally be broken down into 2 categories.

The first type of safety limit shuts the ice maker down when it's been in the freeze cycle too long and the second is when it stays in the harvest cycle too long.  If either limit is reached, it's an indication that the ice machine is not working properly and needs to be locked out.  It will remain shut down until someone resets the maker, either through the toggle switch or by resetting the power.

Why would a Manitowoc Ice Machine shut down on a long harvest safety limit?

The #1 reason a Manitowoc will shut down on a harvest safety limit is because it's dirty.  A dirty evaporator will hold onto the ice, making it slowly melt away until there is no ice to break the bin switch.  Which leads to the second most common reason for a failed harvest safety limit, bad bin switch.

When Ice falls from the evaporator it opens the water curtain, which breaks the proximity of the bin switch.  If the switch is bad it will not read that the ice has fallen, thus terminating the harvest cycle.  Typically, after 3 consecutive cycles of long harvests, the machine will lock out.

Why would a Manitowoc Ice Machine shut down on a long freeze cycle?

This safety limit is a little more difficult to diagnose than a long harvest, however is most commonly associated with a water problem.  If there is not enough water in the trough or able to be pumped over the evaporator, then it cannot make contact with the ice thickness probe.  The ice thickness probe is what would terminate the freeze cycle and initiate a harvest.

Places to look would be a faulty water inlet valve or a dump valve that is stuck open, causing the ice maker to lose all it's water down the drain, before it can freeze.  However, never underestimate a good cleaning, clogged distributor holes or a clogged up pump can also lead to a long freeze time, thus shutting down your Manitowoc ice machine.  In addition, make sure your water level probe is not dirty, causing it to misread, scale build up on the probe will tell the board that it's full of water.

Most common parts replaced on a Manitowoc Ice Machine:

Ice Thickness Probe
Water Level Probe