New Holland ATC 133 – ATC (Automatic Temperature Control) controller: Low pressure switch (-) input is shorted to ground

The controller has detected an electrical short to ground on the negative input circuit of the A/C low-pressure switch, which monitors the refrigerant pressure in the air conditioning system to prevent the compressor from running when the pressure drops too low.

• T5 Series
• T6 Series
• T7 Series
• T8 Series
• T9 Series
• TG Series
• TG210
• TJ Series
• TJ325
• T9.390
• CR Series
• CR9040
• CR9090
• CX Series
• CX8070
• CX8090
• FR Series
• FR600
• FR850
• L223
• L225
• L230
• C232
• C238

1. 1

   Check refrigerant levels to ensure a physical refrigerant leak is not causing irregular A/C cycling or masking the issue.

2. 2

   Visually inspect the wiring harness and all connectors between the low-pressure switch and the ATC controller for chafed wires, bare insulation, or pinched harnesses grounding out against the chassis.

3. 3

   Perform a voltage test: Turn Keyswitch ON, set ATC Switch to DEFOG, disconnect harness at the low-pressure switch, and test for 5 Volts. No voltage indicates a failed ATC controller or harness break/short. 5V indicates an internally failed switch.

1. 1

   Power Down

   Turn off the machine and disconnect the battery ground if you need to perform wiring repairs.

2. 2

   Harness Repair

   If damage to the connectors or wiring was found during the visual inspection, repair or replace the affected harness section. Clear all fault codes and test the system.

3. 3

   Switch Replacement

   If the wiring and controller tested fine, replace the low-pressure switch.

4. 4

   Disconnect Connector

   Disconnect the weather-sealed electrical connector from the A/C low-pressure switch.

5. 5

   Remove Old Switch

   Unthread the old switch from the A/C low-side service port.

6. 6

   Install New Switch

   Thread the new OEM switch onto the port and tighten securely.

7. 7

   Reconnect Connector

   Reconnect the electrical connector.

8. 8

   Reset System

   Toggle the ATC switch to OFF, then to the appropriate operational mode to reset the system. Clear the fault codes from the ATC module and run the A/C to verify it blows cold and the compressor engages properly.