Case IH 128 – ATC (Automatic Temperature Control): High pressure switch (-) input is shorted to ground

The system has detected a short to ground condition on the circuit for the Air Conditioning (A/C) high-pressure switch. Because this switch is a normally closed switch, a short to ground on either wire leading to the switch can trigger this code.

• STX Steiger
• MX Magnum series
• TG series
• Steiger series (STX, 350-600)
• Puma series
• Maxxum series
• AFX8010
• T8.xxx series
• T8020
• T8040
• TG215

1. 1

   Visual Inspection: Inspect the A/C high-pressure switch wiring harness and all connectors for physical damage, rubbing, or exposed wires that could be grounding out against the machine's frame.

2. 2

   Harness Continuity Test: Disconnect the harness lead to the A/C high-pressure switch. Use a multimeter to test both the positive and negative wires in the harness for continuity to ground.

3. 3

   Switch Test: Test the high-pressure switch for internal shorts to its casing. Under normal system pressures, the switch should have continuity across its terminals (normally closed) but should not have continuity to the switch body/ground.

4. 4

   Controller Test: If the harness and switch both test good, the ATC controller itself may be internally shorted and failing to read the circuit correctly.

1. 1

   Locate the Switch

   Find the A/C high-pressure switch, which is typically threaded into the A/C compressor or the high-pressure A/C line.

2. 2

   Disconnect Power

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

3. 3

   Repair Wiring (If Applicable)

   If the diagnostic tests revealed a chafed wire, repair the damaged section of the wiring harness using heat-shrink connectors and re-loom the harness to prevent future rubbing.

4. 4

   Replace the Switch (If Applicable)

   Disconnect the electrical connector from the switch. Note: Check if the switch is mounted on a Schrader valve. If it is, you can unthread it without losing refrigerant. If it is not, the A/C system must be properly evacuated by a certified technician before removal. Thread the new switch into place and reconnect the harness.

5. 5

   Replace the ATC Controller (If Applicable)

   If the wiring and switch are perfectly fine, replace the ATC module located in the cab console.

6. 6

   Clear Codes and Test

   Reconnect the battery, use the electronic service tool or the tractor's diagnostic monitor to clear the stored fault codes, and run the A/C system to verify the repair.