Case IH 191 – Engine Controller (Engine ECU): ATC clutch driver shorted to ground when ON

The Engine Electronic Control Unit (ECU) has detected a short circuit to ground in the driver circuit that engages the Automatic Temperature Control (ATC) clutch (the A/C compressor clutch). When the system commands the clutch to turn ON, the current draw exceeds safe parameters due to the short, prompting the controller to log the permanent fault and disable the circuit to prevent electrical damage.

• MX Magnum
• STX Steiger
• MX210
• MX230
• MX255
• MX285
• MX305
• Magnum 215-335

1. 1

   Inspect the wiring harness running from the Engine ECU to the A/C compressor (ATC) clutch for chafed insulation, melted wires, or pinch points touching the chassis.

2. 2

   Disconnect the electrical connector at the A/C compressor clutch and measure the resistance of the clutch coil with a multimeter (near zero ohms indicates an internal short).

3. 3

   With the clutch disconnected, use a multimeter to check the ATC clutch driver wire for continuity to ground to isolate a harness short.

4. 4

   Verify the pins at the Engine ECU connector for corrosion or damage that could be bridging the circuit to a ground pin.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to ensure safety while working on the electrical and engine systems.

2. 2

   Recover Refrigerant

   Using an approved A/C recovery machine, evacuate the R134a refrigerant from the HVAC system.

3. 3

   Remove the Drive Belt

   Relieve tension on the A/C compressor belt and remove it from the compressor pulley.

4. 4

   Disconnect Lines and Wiring

   Unplug the ATC clutch electrical connector. Disconnect the high and low-pressure refrigerant lines from the compressor. Cap the lines immediately to prevent moisture from entering the system.

5. 5

   Remove the Compressor

   Unbolt the A/C compressor from its mounting bracket and remove it from the engine bay.

6. 6

   Install the New Compressor

   Mount the new A/C compressor (which includes the new ATC clutch) and torque the mounting bolts to OEM specifications.

7. 7

   Reconnect Lines

   Install new O-rings on the refrigerant lines, lubricate them with a small amount of PAG oil, and bolt the lines to the new compressor. Reconnect the ATC clutch electrical connector.

8. 8

   Reinstall the Belt

   Route the A/C compressor belt back onto the pulleys and restore tension.

9. 9

   Evacuate and Recharge

   Pull a vacuum on the A/C system to remove air and moisture. Recharge the system with the correct capacity of R134a refrigerant and PAG 100 oil. (Note: For MX Magnum 215–335 models, the system takes 2100g of R134a and 290ml of PAG 100 oil).

10. 10

    Clear Codes

    Reconnect the battery. Use a diagnostic tool (such as Jaltest or the Case IH Pro monitor) to clear the permanent fault code 191. Run the tractor and engage the A/C to verify the ATC clutch engages without logging the code.