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

Manitowoc Control Board Testing

Manitowoc control boards are arguably the most reliable ice maker control board in the industry.  In comparison to the number of failures of other components within a Manitowoc ice maker, the control board is one of the least replaced.  Usually an external factor will cause the control board failure, like a power surge, not a failure of components.

To test a Manitowoc control board you must first be familiar with your specific models sequence of operations.  The order of which components are energized by the board or sequence of operations, are published online via the official Manitowoc website.  Be sure to reference your specific model number, because not all Manitowoc ice makers have the same operation sequence.

The next step is simply following the sequence and checking to make sure the components that should be getting power, are receiving the proper voltage.  For example, if the dump valve is supposed to be energized, before the freeze cycle initiates, then check to make sure it is getting voltage.  If the dump valve is receiving the proper power supply, you can rest assured the board is working correctly, at least in this stage of the control board diagnosis.

If a component listed on the Manitowoc sequence of operations receives constant voltage or is energized out of sequence, then that's a good indication that you have a bad control board.  Usually, a sticking relay on the board will be at fault, in this case the entire board would need to be replaced.

Physical examination is another method for determining if you have a faulty control board.  Burn marks can be easy to spot and usually indicate that the board is no longer functioning properly.  Again, separate components are the Manitowoc control board cannot be replaced, you must replace the entire board.

Below are the 2 most common control boards in the field, please verify with the manufacturer which board is used on your machine.

Manitowoc S Series Control Board - $291.41
Manitowoc Q Series Control Board - $483.00

Manitowoc Water Pump Problems

Manitowoc water pumps are another commonly replaced item on an ice machine.  Over time they can either lock up or, as hard as it is to believe, gain strength.  What can happen is the pump will eventually increase in power, forcing water too fast through the distribution tube.

When water comes out of the distribution tube too fast, it does not allow the water to cascade down the evaporator, instead splashes over the water curtain. Ice will not form properly or efficiently when this happens, luckily there are 2 ways to fix this issue.

The first fix is to simply apply a clamp to the molded tubing running from the water pump to the distribution tube. This will slow the water flow and allow the water to exit the distribution tube properly. Another option is to simply replace the water pump.

Most Q Series Manitowoc ice makers and older use only 2 different pumps. There is a 115v water pump and a 208-230v water pump, that will work in most cases. If you have an S Series Manitowoc ice maker then your water pump will be different, depending on which model number you have. You can purchase both pumps for just $222.18 from IceMakerPartsShop.com


115v Water Pump - $222.18
208-230v Water Pump - $222.18

Ice Maker Season Is Almost Over

The commercial ice machine business is coming to a close.  Once school starts back up, it normally means a slow down in ice maker service calls and general equipment sales.  So, it becomes important to start focusing on preventative maintenance.

During the summer months it seems that everyone is too busy and simply puts quick fixes in place to keep the ice maker pumping out cubes.  Now is the time to catch up on those PMs and increase your familiarity with the commercial ice makers.  Thankfully there are a number of free tools available online to help with your knowledge of commercial ice machines.

For example, did you know that Manitowoc has online service classes for free? Anyone can signup and login and go through a brief course, split into many different categories. Each class is even automated to test the user at the end of the presentation.

In addition, there is literature available for download, for free. Service Technician Handbooks are available in PDF format, which can be placed on your smart phone. That way there is less of a reason to keep books on your service truck, since you have your phone with you everywhere. Also, having a service handbook in PDF format allows for quick electronic searches.

So, start stocking up on literature now, either in electronic form or by printing them out. This will help ensure you are more efficient next time you are in front of a commercial ice maker.

Welcome To Commercial Ice Talk

This blog was crated to facilitate an open discussion and go-to location for commercial ice machine preventative maintenance, tips, diagnosis, and deals on replacement parts and equipment.  Most major brands will be covered at one time or another on this website, such as Ice-O-Matic, Scotsman, Hoshizaki but the primary focus will be on the market leader, Manitowoc.

Each week will have at least one new post and theme.  Comments will remain open so that a discussion can take place and answers can be addressed.  If pertinent questions are brought up, they will be added to the original post, to help with reading search engine awareness.

Please feel free to suggest topics or questions.