Case IH 16120 – Cab Controller / ATC (Automatic Temperature Control) Module: Blower speed select potentiometer open or shorted to power.

This code indicates a circuit failure where the controller is receiving a voltage signal from the blower speed selection dial (potentiometer) that is either completely missing (open circuit) or abnormally high (shorted to a power source). When this occurs, the system cannot determine the operator's requested fan speed, which typically causes the HVAC system to default to an automatic blower speed or disable manual control.

• Puma/Mid Range Magnum
• Maxxum
• Puma Series Tractors (125, 140, 165, 180, 195, 210, 225 CVX)
• Magnum Series Tractors (MX210, MX230, MX255, MX285, 310)
• Steiger Series Tractors
• Axial-Flow Combines (5088, 6088, 7088)

1. 1

   Inspect the Control Panel: Check the physical condition of the blower speed dial on the climate control panel. Does it feel loose or lack resistance?

2. 2

   Check Connections: Access the rear of the climate control panel. Disconnect the harness and inspect the pins for corrosion, pushed-out terminals, or moisture.

3. 3

   Test for 5V Reference and Ground: Using a multimeter, verify that the potentiometer is receiving its 5V reference signal and has a solid ground from the Cab Controller.

4. 4

   Test the Potentiometer (Sweep Test): Measure the resistance across the signal and ground pins of the potentiometer while slowly turning the dial. The resistance should change smoothly. If the reading drops out to infinity (open) or stays static, the potentiometer is internally failed.

5. 5

   Harness Continuity: If the switch tests fine, check the signal wire between the climate control panel and the Cab Controller for continuity, and ensure it is not shorted to a 12V power source in the cab harness.

1. 1

   Power Down

   Turn off the machine and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Access the HVAC Controls

   Carefully pry off or unscrew the cab interior trim panels surrounding the A/C and heater control unit (usually located on the right-hand console or B-pillar, depending on the model).

3. 3

   Remove the Control Unit

   Remove the retaining screws holding the climate control module in place and pull it forward.

4. 4

   Disconnect Harnesses

   Unplug the electrical connectors from the back of the unit.

5. 5

   Replace the Component

   Depending on the specific model, the blower potentiometer may be a replaceable switch on the board, or you may need to replace the entire HVAC control module assembly. Swap the faulty component.

6. 6

   Reassembly

   Plug the wiring harnesses back in, secure the control module with its retaining screws, and snap the trim panels back into place.

7. 7

   Test Operation

   Reconnect the battery, turn the ignition to the ON position, and clear the inactive fault codes via the AFS monitor or instrument cluster. Test the blower motor through all speed settings to verify the repair.