Case IH 518502-03 - BCM – BCM: Air Conditioner Clutch Solenoid Driver - Voltage Above Normal, Or Shorted To High Source

The control circuit is detecting battery voltage (B+) when it should not be. This is typically caused by a wiring harness shorting to a power wire, a welded relay sending constant power, or an internal short within the control module's driver circuit.

• MAGNUM AFS Connect
• Magnum tractors
• Steiger tractors
• Axial-Flow combines

1. 1

   Use a bidirectional scan tool to manually command the A/C clutch ON and OFF to determine if the BCM can control the circuit or if the driver is permanently shorted.

2. 2

   Perform a circuit load test at the A/C compressor clutch connector using a load device (like a headlight bulb) to verify adequate amperage, rather than relying solely on a multimeter.

3. 3

   Verify the A/C clutch relay is receiving its ground control signal from the BCM and ensure the relay contacts are not stuck closed.

4. 4

   Verify proper refrigerant pressure and pressure switch readings via live data to rule out secondary HVAC issues.

1. 1

   Isolate the Component

   Turn the machine off and disconnect the electrical connector at the A/C compressor clutch solenoid. Turn the key back on and check if the 518502-03 fault code changes status (e.g., from 'Short to B+' to 'Open Circuit').

2. 2

   Inspect the Relay

   Locate the A/C clutch relay in the junction box. Remove the relay and test it for internal shorts (welded contacts). Swap it with a known good relay of the same type. If the clutch operates normally and the code clears, replace the relay.

3. 3

   Harness Inspection

   If the relay is good, trace the wiring harness from the BCM to the relay, and from the relay to the A/C compressor. Look for chafed wires, melted insulation, or pinched harnesses where the clutch power wire might be touching a constant 12V (B+) source.

4. 4

   Test the Clutch Coil

   Measure the resistance of the A/C compressor clutch field coil. If the coil has zero resistance (internal short), it can cause excessive current draw that damages the relay or driver.

5. 5

   Repair and Clear

   Repair any shorted wiring, or replace the shorted clutch coil/relay. Clear the fault codes using a scan tool and run the A/C system on MAX to verify the clutch cycles properly without setting a new code.