Case IH 518507-14 - BCM – BCM: A/C compressor low pressure switch circuit - invalid input voltage

The controller is detecting an 'invalid input voltage' from the A/C compressor low pressure switch circuit. This means the voltage returning from the low pressure switch to the controller is outside the expected parameters (e.g., shorted to ground, shorted to power, or an open circuit), preventing the system from accurately determining if there is enough refrigerant pressure to safely run the A/C compressor.

• MAGNUM AFS Connect
• Magnum series (MX100 to MX285, 7210-7250, 8910-8950)
• Steiger/Quadtrac (STX325, STX440, 9270, 9370)
• Maxxum (5120-5150, MX100C-MX135)
• CX series (CX50-CX100)
• Legacy models (485-895, 786-1586, 3088-7488)
• Axial-Flow series (1420-1688, 2144-2188, 2366-2388, 7230, 7240)
• Cotton Pickers (782, 1800-2055)
• Swathers (4000, 5000)
• Case loaders/dozers

1. 1

   Check refrigerant levels to ensure the A/C system has a proper charge; if empty, the switch will remain open to protect the compressor.

2. 2

   Visually inspect the wiring harness and pigtail connector at the A/C low pressure switch for chafed wires, melted insulation, or corrosion inside the connector pins.

3. 3

   With the key ON and engine OFF, use a multimeter to check for the proper reference voltage at the switch connector and verify ground circuit continuity to the chassis/battery ground.

4. 4

   Unplug the switch and test it for continuity based on its specific Normally Closed or Normally Open specifications; if the system is charged but continuity is incorrect, the switch has failed internally.

1. 1

   Locate the Switch

   Find the A/C low pressure switch, typically located on the suction line (the larger diameter A/C hose) between the evaporator and the A/C compressor.

2. 2

   Disconnect Power

   Turn off the machine and disconnect the battery ground to protect the BCM.

3. 3

   Disconnect the Connector

   Unplug the electrical connector from the low pressure switch.

4. 4

   Remove the Switch

   Unscrew the faulty switch from the A/C line. (Note: Most modern Case IH low pressure switches are mounted on a Schrader valve fitting, meaning you can unscrew the switch without discharging the A/C system. Verify this before removal to avoid venting refrigerant).

5. 5

   Install the New Switch

   Lubricate the O-ring on the new switch with a drop of clean PAG refrigerant oil. Thread the new switch onto the fitting (many use a 7/16"x20 or M10 thread) and tighten to the manufacturer's specified torque. Do not overtighten.

6. 6

   Reconnect

   Plug the electrical connector back in and reconnect the battery.

7. 7

   Clear Codes & Test

   Use a diagnostic tool to clear the 518507-14 code from the BCM. Start the machine, turn on the A/C, and verify that the compressor clutch engages and the cab cools properly.