Polar King Walk-In Cooler Alarm T3 COIL SENSOR: Shorted or Open
T3 COIL SENSOR is an alarm on the KE2 evaporator control: the coil temperature sensor is shorted or open. The document lists the trigger only. Look for ice on the coil, check the box temperature and clear the alarm once to see if it returns.
Medium: a sensor input is lost, and defrost behavior may be affected, though the document does not say.
- Code
- T3 COIL SENSOR
- Maker
- Polar King
- Equipment
- Walk-in coolers & freezers
- Applies to
- Polar King walk-in coolers/freezers with KE2 Evaporator Efficiency Evap OEM board (Basic Display / Combo Display)
What does Polar King T3 COIL SENSOR mean?
A coil temperature sensor on the evaporator, called T3 by the KE2 Evaporator Efficiency board, tells the control how cold the coil is, which matters for defrost decisions. When the sensor circuit is shorted or open, the board raises T3 COIL SENSOR in its Alarms Status Menu. The Combo Display names it; the Basic Display shows only a red or yellow light. The installation instructions give the trigger, shorted or open, and no cause or repair. The only handling they mention is the CLEAR ALARMS menu item. Since the document does not describe what the board does without the coil reading, we cannot say whether defrost is affected. A coil that is icing up despite normal operation, or a defrost that seems to be ending oddly, would fit a lost coil reading but would also fit other problems.
Affected models and control systems
Polar King walk-in coolers and freezers fitted with the KE2 Evaporator Efficiency Evap OEM board, with either the Basic Display or the Combo Display. The alarm is listed in the Alarms Status Menu, which is view only, on page 14 of the KE2 installation instructions.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- Alarm light on the Basic Display
- T3 COIL SENSOR on the Combo Display
- Frost building on the evaporator coil
Possible causes
Likely causes — what usually sits behind T3 COIL SENSOR on this control. A technician confirms which one it is before any part is replaced.
- A coil sensor clip that has come off the fin or tube
- A sensor cable burned or brittle near the defrost heater
- Ice around the sensor lead pulling it loose
Safe checks before calling for service
- Look at the evaporator coil from outside the cover for heavy frost, without chipping at it.
- Check the walk-in temperature with a thermometer.
- Clear the alarm using CLEAR ALARMS and watch whether T3 COIL SENSOR returns.
- If it returns, note whether frost is present and arrange service.
How a technician diagnoses T3 COIL SENSOR
- Read the alarm and check the defrost history.
- Inspect the coil sensor mounting and the lead near heaters and drain pan.
- Measure sensor resistance and compare it with the chart.
- Check cable continuity to the board.
- Replace the sensor and run a defrost to confirm normal behavior.
- The evaporator coil area has defrost heaters wired to line voltage, so working near the coil sensor is not an operator task. Interpreting the effect on defrost needs the control settings for that box. Scraping ice off a coil can puncture the refrigerant tubing.
How T3 COIL SENSOR differs from similar codes
T3 is the coil temperature sensor. It differs from T1 on the suction line and T2 in the return air.
Technical reference
- Document
- KE2 Evaporator Efficiency Installation Instructions N.1.1 (posted on polarking.com Downloads as ke2-installation.pdf; authored by KE2 Therm Solutions)
- Edition
- N.1.1 July 2015
- Models / control
- Polar King walk-in coolers/freezers with KE2 Evaporator Efficiency Evap OEM board (Basic Display / Combo Display)
- Section
- Alarms Status Menu (view only), p. 14 (Alarm Status Menu listed p. 13)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Polar King walk-in cooler & freezer error codes
Why does the coil sensor matter?
The document names it only as the coil temperature sensor, but coil temperature is how a controller usually judges defrost.
Should I chip ice off the coil?
No. That can damage the coil.
Will CLEAR ALARMS remove the problem?
No, only the stored alarm. A bad sensor will bring it back.
Need help with Polar King T3 COIL SENSOR?
A technician confirms the cause on site and gives you the price in writing before any work starts.