New Holland ATC 126 – ATC (Automatic Temperature Control) controller: High pressure switch (+) input shorted to ground

This code indicates that the control module has detected a short-to-ground condition on the positive (+) side of the Air Conditioning (A/C) high-pressure switch circuit. Because the high-pressure switch is a normally closed switch, the short to ground could be present on either wire leading to the switch.

• T6
• T7
• T8
• T9
• CR9090
• CX8080 Elevation
• CX8090 Elevation (Tier 4A)
• SP280
• SP480
• L218
• L220
• L221
• L228
• C227
• C232
• C238

1. 1

   Visually inspect the wiring harness and all connectors between the A/C high-pressure switch and the ATC controller for chafing, rubbing, or pinched wires that could cause a short to ground.

2. 2

   Turn the key switch to the ON position to prepare for harness isolation.

3. 3

   Disconnect the connector at the high-pressure switch and measure voltage/resistance on the pins to determine if the short to ground is in the wiring harness or if the switch itself has failed internally.

4. 4

   If the wiring harness tests fine and the switch is not internally shorted, check the ATC controller for an internal failure.

1. 1

   Disconnect Power

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

2. 2

   Locate the Switch

   Locate the A/C high-pressure switch, which is installed on the high-pressure side of the A/C line (often near the compressor or receiver drier).

3. 3

   Repair Wiring (If Applicable)

   If your diagnostic checks revealed a chafed wire shorting to the frame, repair the damaged section of the wiring harness using weather-sealed connectors and re-loom the harness to prevent future rubbing.

4. 4

   Replace the Switch (If Applicable)

   If the switch is faulty, unscrew it from the A/C line. Note: On most modern New Holland equipment, this switch is mounted on a Schrader valve fitting, meaning it can be unscrewed and replaced without having to recover and recharge the A/C refrigerant.

5. 5

   Install New Part

   Thread the new switch onto the fitting (common thread sizes are M10 x 1.25 or 7/16" x 20) and tighten securely. Reconnect the electrical harness.

6. 6

   Clear Codes

   Reconnect the battery, turn the key ON, clear all fault codes from the ATC module, and run the A/C system to verify the repair.