Case IH 131 – ATC (Automatic Temperature Control) module: Low pressure switch (+) input shorted to ground.

The system has detected a short circuit to ground on the positive signal wire of the A/C low-pressure switch. This circuit is part of the "Low Pressure Switch Clutch Latching Circuit," which is designed to monitor refrigerant pressure and protect the A/C compressor from running dry.

• STX Steiger
• Magnum MX215
• Magnum MX245
• Magnum MX275
• Magnum MX305
• Magnum 235-340 (Series 4)
• Steiger 280
• Steiger 350
• Steiger 385
• Steiger 435
• Steiger 485
• Steiger 500
• Steiger 530
• Steiger 535
• Steiger 600
• STX 280
• STX 350
• STX 385
• STX 435
• STX 485
• STX 500
• STX 530
• STX 535
• STX 600
• Puma 165
• Puma 180
• Puma 195
• Puma 210
• Puma 225
• Maxxum 125
• AFX8010
• 6140
• 8240

1. 1

   Visually inspect the wiring harness between the ATC control module and the A/C low-pressure switch for chafing, pinched wires, or damaged connectors touching the chassis.

2. 2

   Disconnect the electrical connector at the low-pressure switch and use a multimeter to check for continuity between the positive signal wire (e.g., pin A-15 or connector X022) and a clean chassis ground.

3. 3

   Perform a controller-based resistance test: If continuity to ground exists while the switch is unplugged, the short is in the wiring harness. If the short disappears when the switch is unplugged, the switch itself is internally shorted to its metal housing.

1. 1

   Turn off machine and disconnect battery

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

2. 2

   Locate the A/C low-pressure switch

   Locate the A/C low-pressure switch, which is typically threaded onto the low-pressure A/C line near the receiver drier or evaporator.

3. 3

   Disconnect wiring harness

   Disconnect the wiring harness from the switch.

4. 4

   Repair harness or replace switch based on diagnostics

   Based on your diagnostic continuity test: If the harness is shorted: Trace the specific signal wire (often labeled 907, 908, or 909 depending on the chassis) back to the ATC module. Repair the damaged insulation or splice in a new section of wire where it is grounding out against the frame. If the switch is shorted: Unthread the faulty low-pressure switch from the A/C line (most are mounted on a Schrader valve, meaning you will not lose refrigerant charge when removing it, but verify your specific model's setup). Thread the new OEM switch into place and tighten to spec.

5. 5

   Reconnect electrical connector

   Reconnect the electrical connector to the switch.

6. 6

   Reconnect battery and clear codes

   Reconnect the battery, turn the key on, and clear the ATC fault codes via the cab display.

7. 7

   Verify A/C system operation

   Engage the A/C system to verify that the compressor clutch latches properly and the code does not return.