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Error code reference

U-Line Ice Maker Error Code R Zone T Open

Right zone thermistor circuit is open.

U-Line codesU-Line ice maker codes

Right zone thermistor circuit is open.

First step from the service manual

Check connection. Replace if necessary.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What R Zone T Open means on a U-Line ice maker

The R Zone T Open error on a U-Line ice maker indicates that the control board is detecting an open circuit condition in the right zone thermistor circuit. A thermistor is a temperature-sensing resistor whose resistance changes predictably with temperature. When the circuit reads as open, it means the board is receiving no valid resistance signal from that sensor, which prevents the unit from accurately monitoring temperatures in the right zone and managing its refrigeration cycle correctly.

Open circuit faults in thermistor loops are most commonly caused by a physical disconnection at the wiring harness connector, a broken wire in the sensor lead, or a failed thermistor itself. Thermistors can fail internally, causing the resistance to read as infinite rather than the expected value at a given temperature. Connector pins can corrode, back out of their housing, or become loose over time, especially in the cold and humid environment inside an ice maker.

Diagnosis should begin at the connector, inspecting it for corrosion, bent pins, or loose seating. If the connection is intact, measure the thermistor resistance directly across its terminals and compare the reading to the expected resistance curve for the operating temperature. An infinite or open resistance reading confirms thermistor failure and replacement is required. If resistance reads correctly at the sensor but the fault persists, the wiring harness between the sensor and the control board should be inspected for continuity.

Source: manufacturer service documentation.

Common causes of R Zone T Open

  1. 01

    Loose or disconnected wiring connector

    Wiring / connection

    The connector at the thermistor or along the wiring harness may have worked loose, interrupting the circuit. Inspect all connectors in the right zone thermistor circuit for proper seating and signs of corrosion.

  2. 02

    Failed thermistor

    Part replacement

    The thermistor itself may have failed internally, causing it to present infinite resistance instead of the expected value. A multimeter reading of open or infinite resistance across the thermistor terminals confirms this failure.

  3. 03

    Broken or damaged wire in the sensor lead

    Part replacement

    A wire in the thermistor lead may be broken internally while still appearing intact externally. Inspect the harness for pinch points, kinks, or damage and test each wire for continuity.

  4. 04

    Corroded connector pins

    Wiring / connection

    The humid, cold environment inside an ice maker can cause corrosion to build up on connector pins over time, increasing resistance to the point of an open circuit. Check pins visually and clean or replace the connector if corrosion is present.

  5. 05

    Control board fault

    Part replacement

    If the thermistor and all wiring check out correctly but the error persists, the control board input circuit may have failed. This is the least likely cause and should only be considered after all other components are confirmed good.

See the test procedure for each cause

Frequently asked questions about R Zone T Open

What does R Zone T Open mean on a U-Line ice_maker?
R Zone T Open means the control board is detecting an open circuit in the right zone thermistor, which is the temperature sensor for that section of the unit. The board cannot read a valid resistance value from the sensor, so it cannot monitor temperatures correctly. This is typically caused by a loose connector, a broken wire, or a failed thermistor.
Can I fix the R Zone T Open error myself?
If the cause is simply a disconnected or loose wiring connector, you may be able to resolve it by reseating the connector yourself. If the thermistor has failed or a wire is broken, replacing those components requires basic electrical skills and a multimeter to confirm the fault. Control board replacement should generally be handled by a qualified technician.
Is it safe to continue using my U-Line ice maker when this error appears?
You should not continue using the unit while this error is active. Without a functioning right zone thermistor, the control system cannot properly regulate temperatures, which can lead to inadequate ice production, food safety issues, or further component damage. Address the fault before resuming normal operation.
How much does it cost to repair the R Zone T Open error?
If only a wiring connection needs to be reseated, there may be no parts cost at all. A replacement thermistor typically costs in the range of $15 to $60 depending on the specific part. If a control board replacement is needed, parts and labor costs can range from $150 to $400 or more.
Will resetting my U-Line ice maker clear the R Zone T Open error?
A reset may temporarily clear the error code from the display, but it will return as soon as the control board polls the thermistor circuit again and detects the same open condition. The underlying cause, whether a bad connection, broken wire, or failed thermistor, must be physically diagnosed and repaired before the error will clear permanently.

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