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How to Resolve the E24-T4 Error Code on Manitowoc Ice Makers

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Manitowoc ice machines are common in commercial kitchens, so it’s important to be familiar with their error codes and how to fix them. Today, we’re looking at the E24-T4 error code on the Manitowoc Indigo ™ ice maker. This code indicates a temperature sensor issue.

Don’t confuse the E24-T4 error with the E4 error. While both are related to temperature, solving the E4 error will have you cleaning condenser coils. This may be necessary, but it’s not the cause of this specific error code.

The E24-T4 error code occurs when thermistors aren’t functioning properly.  A thermistor is, as the name implies, a heat-sensitive resistor. Because its resistance changes in proportion to temperature fluctuations, it is used in icemakers to control temperature.

In Manitowac machines, thermistor readings are monitored continuously and are reported based upon six-second averages. If the average temperature falls outside acceptable ranges – either hot or cold – the error code occurs.

A malfunctioning thermistor may cause the machine to quit making ice or cause the ice maker to display incorrect and wildly fluctuating temperatures – like 20-degree Fahrenheit differences – in only a few minutes.

Thermistor failures can be traced to a few things. Because they lose accuracy over time, they may simply be old. Alternatively, they may have been damaged by heat, improper handling (such as during delivery and installation), or a mismatch of device to application (such as a prior replacement).

Before deciding to replace the thermistor, confirm that it is, indeed, the problem.

On Manitowoc’s Indigo™ series, press the Menu button. Scroll to Services, then Diagnostics, and then Temp Sensors. (To get to each menu, press the “right” arrow.) The Temp Sensors tab will display the thermistor temperature readings. Compare your actual readings to the chart in the technicians’ manual.

temp chart
  • An open thermistor will display -22°F (-30°C). This is perhaps the most common thermistor problem. It may be caused by a separation between the lead materials and the resistor elements.
  • If the temperature fluctuates dramatically while you are taking readings, the problem is drifting resistance values, caused by component aging or recently altered operating parameters (moving the machine from an inner hallway to an external pool patio, for example).
  • If the temperature is 475°F (246°C), there is a short in the system. This is relatively rare, however.

Next, test the T4 thermistor itself. The Manitowoc Indigo™ series has four thermistors (T1, T2, T3 and T4). The T4 thermistor is located on the “evaporator out, first circuit” of each of the Indigo™ models, according to the manual. (For reference, the T1 thermistor is located on the receiver inlet of liquid condenser lines; the T2 is on the compressor discharge or receiver outlet; and the T3 is on the evaporator in or the evaporator out for second circuit or second compressor lines.)

Disconnect the T4 thermistor from the control board and measure both resistance and temperature. Compare your readings with those published in the technical manual. If they are within 10% of the published readings, the thermistor is operable. If they vary by more than 10%, the thermistor is defective.

If the thermistor isn’t the problem, test the control board. With the thermistor disconnected from the control board, check the display temperature reading. According to the manual, if it drops to -22°F (-30°C), the control board is good. A second test, listed by Manitowoc as “short thermistor pins,” says, “The display temperature reading, climbing to 475°F (246°C) indicates the control board is good.

This should solve the issue.

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