New Holland ATC 122 – ATC (Automatic Temperature Control): Mode Select Pot Open Or Shorted To Power

The control module has detected an electrical fault—specifically an open circuit or a short circuit to a power source—in the mode door selector potentiometer circuit.

• T6 series
• T7 series
• T8 series
• T9 series
• T6000 series
• T6010-T6070
• TG series
• TG215
• TG255
• TL series
• TM series
• TS series
• CR series
• CR9090
• CR8.90
• CX series
• CX8080
• CX8090

1. 1

   Perform a functional test using the ATC display by activating the mode control switch and observing the mode door indicator. If the indicator does not change, proceed to electrical testing.

2. 2

   Disconnect the overhead HVAC control module connector (e.g., C079) and turn the ignition switch to the ON position.

3. 3

   Check voltage between the potentiometer's 5V reference pin (e.g., pin 4 on C079) and ground using a multimeter. Expected reading is approximately 5.0 Volts.

4. 4

   Evaluate voltage readings: 0V indicates an open circuit (trace wiring between overhead connector and HVAC floor module controller), >5.8V indicates a short to power (trace wiring to find short to 12V), and ~5.0V indicates good wiring but a failed potentiometer or ATC controller.

1. 1

   Resolve Wiring Issues

   If the diagnostic tests revealed an open or shorted wire, repair or replace the damaged section of the HVAC wiring harness.

2. 2

   Replace the Potentiometer

   If the wiring tests normal (5V reference and good ground are present), the mode select potentiometer itself has failed internally. Remove the overhead or side console panel to access the HVAC control switches, remove the retaining hardware for the rotary switch, and install the new potentiometer.

3. 3

   Reassemble and Reconnect

   Plug all HVAC connectors back into the ATC module and the new potentiometer.

4. 4

   Clear Codes and Retest

   Turn the ignition ON, clear all fault codes from the ATC module, and test the operation of the HVAC mode doors.

5. 5

   Controller Replacement

   If the wiring is perfect, the potentiometer is new, and the ATC 122 code immediately re-displays, the ATC controller has suffered an internal failure and will need to be replaced (contact dealer support/ASIST before condemning the controller).