Case IH 122 – ATC (Automatic Temperature Control) module: Mode Door potentiometer open circuit or shorted to power.

The Automatic Temperature Control (ATC) module has detected an open circuit or a short-to-power condition at the mode door potentiometer. The mode door controls the direction of the airflow in the cab's HVAC system. Possible failure modes include a failed mode door selector/potentiometer, wiring harness damage, or an internal failure of the ATC controller.

• STX Steiger
• Case IH Steiger series (280, 335, 350, 385, 400, 435, 450, 485, 500, 535, 550, 600)
• Case IH Quadtrac series
• Case IH STX series
• Case IH Puma series (Puma 125)
• Case IH Magnum series

1. 1

   Perform a functional test using the ATC display to check the mode door potentiometer by activating the mode control switch on the overhead HVAC control module.

2. 2

   Observe the ATC display while stepping through mode door positions. If the indicator changes, the problem may be intermittent. If it does not change, proceed to electrical testing.

3. 3

   Check for power at the mode door actuator and test for a short circuit to power between the mode door connector and the HVAC module controller.

4. 4

   Inspect the wiring harness for physical damage, pinched wires, or loose/corroded connector pins.

1. 1

   Access the Actuator

   Access the mode door motor/actuator, which is typically located within the cab roof or behind the HVAC control panel depending on the specific tractor model.

2. 2

   Repair Wiring

   If the diagnostic checks revealed an open or shorted wire between the ATC controller and the mode door potentiometer, repair or replace the damaged section of the wiring harness.

3. 3

   Replace the Actuator

   If the wiring and connectors are in good condition and the expected voltage readings are present but the door still fails to operate or report its position, the mode door potentiometer has failed. Remove the mounting screws, disconnect the electrical pigtail, and install a new mode door actuator.

4. 4

   Reassemble and Clear Codes

   Reconnect all connectors, reassemble the cab trim/roof access panels, and use the electronic service tool or cab display to clear all fault codes.

5. 5

   Test Operation

   Test the HVAC system by cycling through all mode door positions to ensure the fault code does not return and airflow is directed properly.