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Resolving Manitowoc Ice Maker T3 and T4 error codes

The vast majority of ice machine problem are caused by improper cleaning. This manifests as error codes, and, erratic temperatures that lead to long harvests. More often than not, can be traced back to mineral build-up inside the machine or dirty coils.  

For example, when the Manitowoc Indigo IY0324A has longer than normal harvest cycles, T3 and T4 fault codes also may appear. They relate to the input and output of the thermistor. First, check inside the evaporator cover to see whether water is flowing evenly across the evaporator and whether there is mineral build-up. Long harvests may be cause by scale build-up on the harvest probe. Cleaning it by soaking it for 10 minutes in Manitowoc’s cleaning solution for 10 minutes, followed by sanitization, should resolve the problem. 

Routine cleaning and sanitizing should be performed every six months. If the machine is exceptionally dirty, take the unit apart for deep cleaning. Note that only Manitowoc Ice Machine Cleaner and Sanitizer are approved for use in Manitowoc ice makers. Using other cleaners may shorten the life of the evaporator and cause harvest problems. Other manufacturers may have similar stipulations, so check the users’ manual.  

Also, never use high-pressure water jets to clean the interior or exterior of ice makers, and be careful to avoid using abrasive equipment and compounds on stainless steel or painted surfaces.  

After cleaning, evaluate all the unit’s conditions. Determine whether the: 

  • ice sheet that forms is complete, even, and about 1/8 inches thick 
  • air filter, condenser, and water sensor also are clean 
  • machine is level front to back and left to right 
  • incoming water temperature is below 70°F and of adequate pressure 
  • water filter is clean and within date 
  • ambient air temperature is below 90°F 
  • evaporator/bin curtain is fully closed 
  • whether lifting the evaporator/bin curtain opens the reed switch (3rd LED at the top of the board) 
  • water goes down the drain from the water reservoir during the freeze cycle 
  • water drains are separate and vented 

If cleaning isn’t the issue, the delta T3 and T4 alarm codes could indicate that the drop between the inlet refrigerant and the tail coil is not within normal parameters. This may be caused by an open thermistor or low charge. Use the keypad to find out. 

To check the faults (T1, T2, T3, or T4) on the Manitowoc Indigo IY0324A, press the Menu button. To check the thermistor temperature readings, scroll to Services and press the right arrow. Scroll to Diagnostics and press the right arrow. Scroll to Temp Sensors and press the right arrow.  

Then, check their accuracy with manual readings.  

First, disconnect the power, and disconnect the thermistor from the control board and measure its resistance. T3 is marked on the left side of the board. If the value your unit displays is within 10% of the resistance value published in the owners’ manual, the thermistor is good. If not, replace the thermistor. 

Then measure the temperature at the thermistor. Compare the measured readings with the readings in the relationship chart in the users’ manual. The T3 (inlet) and T4 (outlet) temperatures associated with the evaporator are only useful five minutes into the freeze cycle. At that point, an open thermistor typically displays -22°F (-30°C). A shorted thermistor will display 475°F (246°C). 

Also consider the ambient air temperature. This model is designed for indoor use, away from direct sunlight and heating vents. Fluctuation in ambient room temperature – either too hot or too cold – can affect ice harvests. Some technicians report the sweet spot for ambient air as 65° to 75°F. 


As a side note, T1 is the liquid line from the condenser and should never be more than 20°F above ambient temperature. T2 is the compressor discharge line. It is used during harvest to ensure the temperature stays above 150°F for this model ice maker. Larger machines are different.