Case IH 16128 – ATC (Automatic Temperature Control) / HVAC Controller: High pressure switch (-) input shorted to ground

The ATC/HVAC controller detects a short to ground on the negative signal wire of the A/C high-pressure switch. Because the controller cannot accurately read the switch's state, it disables the A/C compressor clutch to protect the system.

• Puma/Mid Range Magnum
• Maxxum
• Magnum series (235-340 Series 4, MX/TG series)
• Puma series (140, 165, 180, 195, 210, 225)
• Steiger series
• Axial-Flow series (2166, 2188, 2366, 2388)
• Case wheel loaders
• Case backhoes
• Case skid steers

1. 1

   Visual Wiring Inspection: Locate the A/C high-pressure switch on the high-side A/C line and trace the wiring harness back toward the cab, looking for chafed insulation, pinched wires, or melted spots where the negative wire might be touching the chassis.

2. 2

   Disconnect Test: Unplug the electrical connector at the high-pressure switch and check the negative (-) signal wire for continuity to ground. If the short remains, the harness is faulty; if it disappears, the switch is internally shorted.

3. 3

   Check Cab/Controller Grounds: Verify that the main cab ground strap is clean, tight, and free of corrosion to rule out voltage drops.

4. 4

   Controller Pin Check: Inspect the ATC controller connectors for moisture, corrosion, or bent pins that could be bridging the circuit to a ground pin.

1. 1

   Disconnect battery

   Turn off the equipment and disconnect the negative battery cable.

2. 2

   Repair wiring harness

   If the harness is faulty: Splice and repair the damaged section of the negative signal wire using weatherproof heat-shrink connectors, then re-loom and secure the harness away from vibration points.

3. 3

   Prepare to replace switch

   If the switch is faulty: Locate the high-pressure switch on the A/C line. Check if the switch is mounted on a Schrader valve. If it is, it can be unscrewed directly without losing refrigerant. If it is not, the A/C system must be properly evacuated by a certified technician using a refrigerant recovery machine.

4. 4

   Replace high-pressure switch

   Unscrew the faulty high-pressure switch and install the new OEM replacement switch.

5. 5

   Reconnect electrical connector

   Reconnect the electrical connector to the switch.

6. 6

   Clear fault codes

   Reconnect the battery, turn the key on, and clear the inactive fault codes from the ATC module.

7. 7

   Verify repair

   Start the machine, engage the A/C, and verify that the compressor clutch cycles properly and the code does not return.