Case IH 519051-14 - BCM – BCM: ATC blower speed decrease switch - invalid input voltage

The control module is receiving a voltage signal from the Automatic Temperature Control (ATC) panel's "fan speed down" button that falls outside the expected normal operating range. This is typically caused by a short to ground, a short to power (B+), or an open circuit in the switch or its wiring harness.

• MAGNUM AFS Connect
• Magnum 250
• Magnum 280
• Magnum 310
• Magnum 340
• Magnum 380
• Magnum 400
• Steiger AFS Connect
• Quadtrac AFS Connect

1. 1

   Test the Switch: Gain access to the back of the ATC control panel. Use a multimeter to test the resistance/continuity of the blower speed decrease switch when pressed.

2. 2

   Inspect the Wiring Harness: Trace the wiring harness between the ATC control panel and the BCM. Look for pinched wires, chafing against cab framework, or melted insulation.

3. 3

   Check Connectors: Disconnect the plugs at both the ATC panel and the BCM. Inspect for loose, backed-out, bent, or corroded pins.

4. 4

   Check the Blower Resistor Circuit: Inspect the blower motor resistor and its pigtail connectors for overheating and melting, as a severely shorted blower resistor circuit can sometimes cause erratic voltage feedback to the ATC panel.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery to prevent accidental shorts while working on the cab electronics.

2. 2

   Access the ATC Panel

   Remove the interior cab trim/bezel required to access the HVAC/ATC control head.

3. 3

   Isolate the Fault

   Disconnect the ATC panel. Probe the signal wire for the blower decrease switch at the BCM connector. If the wire is shorted to ground or has infinite resistance (open) while disconnected from the panel, the harness is the issue. Repair or splice the damaged section of the wire.

4. 4

   Replace the ATC Panel (if necessary)

   If the harness tests good, the internal contacts of the blower decrease switch on the ATC board have failed. Because these switches are typically integrated into a single printed circuit board, the ATC control head unit will need to be replaced or sent out for board-level repair.

5. 5

   Inspect the Resistor

   As a preventative measure, remove the blower motor resistor (usually located near the blower housing/evaporator) and inspect the 5-spade connector for melted plastic. Replace the resistor and pigtail if heat damage is present.

6. 6

   Reassembly

   Reconnect all harnesses, apply dielectric grease to the connections, and reinstall the cab trim.

7. 7

   Clear and Test

   Reconnect the battery, turn the key on, clear the inactive BCM fault codes, and test the blower speed decrease button to verify the repair.