Case IH 115 – ATC (Automatic Temperature Controller): Evaporator sensor open or shorted to power

This code indicates a circuit failure related to the A/C evaporator temperature sensor. The sensor is a thermistor that monitors the temperature of the air conditioning evaporator coil to prevent it from freezing over and to protect the A/C system from damage. The fault triggers when the controller detects that the sensor circuit is either completely open (e.g., a broken wire, unplugged connector, or internally failed sensor) or shorted to a power source (voltage reading is too high).

• STX Steiger
• Magnum 235 - 340 (Series 4)
• MX Magnum series
• TG series
• Puma series
• STX series
• 2144
• 2166
• 2344
• 2366
• 2377
• 2388
• 2577
• 2588
• 5088
• 6088
• 7088
• 2155
• CPX420
• CPX610
• CPX620
• 521G2

1. 1

   Locate the evaporator temperature sensor and check the electrical connector to ensure it is fully seated and free of corrosion

2. 2

   Inspect the wiring harness between the evaporator sensor and the ATC module for pinched wires, chafing, or breaks (open circuit), or exposed wires touching a 12V source (short to power)

3. 3

   Unplug the sensor and use a multimeter to measure its internal resistance. If the multimeter reads 'OL' (out of limits/infinite resistance), the sensor is internally open and must be replaced

4. 4

   With the sensor unplugged and the key ON, check the harness side for reference voltage from the ATC. If voltage is present on the signal return wire, there is a short to power in the harness

1. 1

   Turn off the machine and disconnect the battery

   to prevent electrical shorts.

2. 2

   Access the HVAC evaporator core housing

   (usually located under the cab roof panel or behind the seat, depending on the machine model).

3. 3

   Locate the evaporator temperature sensor probe

   which is inserted directly into the aluminum fins of the evaporator core.

4. 4

   Disconnect the electrical pigtail connector from the sensor

5. 5

   Carefully pull the old sensor probe straight out of the evaporator fins

   Be gentle to avoid bending or damaging the delicate fins of the evaporator core.

6. 6

   Insert the new sensor probe into the exact same location in the evaporator fins

   Ensure it is seated to the proper depth so it accurately reads the core temperature.

7. 7

   Reconnect the electrical connector

8. 8

   Reassemble the HVAC housing and cab panels

9. 9

   Reconnect the battery, turn the key ON, and clear the fault codes

   via the diagnostic menu or scan tool.

10. 10

    Run the machine and turn the A/C on

    to verify the compressor engages, the system cools properly, and Fault Code 115 does not return.