Case IH 126 – ATC (Automatic Temperature Control) module: High pressure switch (+) input shorted to ground

The system has detected a short to ground condition on the positive (+) side of the A/C high-pressure switch circuit. Because this switch is normally closed, the short could technically be present on either wire leading to the switch.

• STX Steiger
• Magnum
• Steiger
• Puma
• MX series
• TG series
• Maxxum
• AFX series
• 8010
• Axial-Flow

1. 1

   Visually inspect the wiring harness and all connectors between the A/C high-pressure switch and the ATC controller for chafed wires, pinched harnesses, or damaged connector pins.

2. 2

   Perform a harness short test by turning the key switch ON, disconnecting the high-pressure switch connector (C175 or S-47), and using a multimeter to measure for a short circuit to ground on the harness side.

3. 3

   If the wiring harness tests fine with no shorts to ground, verify if the fault lies internally within the ATC controller itself (less common).

1. 1

   Address Wiring Issues

   If diagnostic checks revealed a damaged wire or connector, repair or replace the affected section of the wiring harness.

2. 2

   Recover Refrigerant

   If the wiring is intact and the switch itself has failed internally (shorted to ground), use an approved A/C recovery machine to safely evacuate the refrigerant from the system.

3. 3

   Remove the Switch

   Disconnect the 2-pin electrical connector from the high-pressure switch. Unthread and remove the faulty high-pressure switch from the A/C line/receiver drier.

4. 4

   Install the New Switch

   Thread the new normally-closed high-pressure switch into place. Reconnect the electrical connector.

5. 5

   Recharge the System

   Evacuate the A/C system using a vacuum pump, then recharge the system with the factory-specified weight of R134a refrigerant.

6. 6

   Clear Codes

   Use the Electronic Service Tool (EST) or the in-cab display to clear the ATC 126 fault code. Run the machine and verify that the A/C operates normally and the code does not return.