New Holland ATC 121 – ATC (Automatic Temperature Control) module / HVAC control module: Temperature select pot open/shorted to power

The control module has detected an open circuit or a short-to-power condition at the temperature selection potentiometer (the dial/switch used to set the cab temperature).

• T8 Series (T8000, T8040, T8.xxx)
• T9 Series (T9000, T9.xxx)
• TG Series (TG215, TG245)
• T6 Series
• T7 Series
• MXM/TM Series
• CR9090
• CX8080
• CX8090
• Magnum Series (235–340 Series 4)
• Steiger
• Puma

1. 1

   Perform a functional display check by activating the AUTO switch and slowly adjusting the temperature select control from maximum low to maximum high, observing if the ATC display reading jumps or drops out.

2. 2

   With ignition ON, disconnect connector C079 at the overhead HVAC control module and check voltage between pin 3 and a good ground (expected reading is approximately 5.0 Volts).

3. 3

   If no voltage is indicated (open circuit cause): Inspect wiring between connector C079 pin 3 and HVAC floor module controller connector C055 pin H.

4. 4

   If voltage exceeds 5.8 Volts (short to power cause): Inspect wiring for a short circuit to power between connector C079 pin 3 and connector C055 pin H.

1. 1

   Repair wiring harness

   If harness damage (open or short) was found during the diagnostic checks, repair the damaged wiring harness.

2. 2

   Reconnect and clear codes

   If the wiring is intact and the expected 5V reading is found, the issue lies within the temperature select potentiometer itself or the ATC controller. Reconnect all connectors and clear all fault codes.

3. 3

   Test HVAC system

   Test the operation of the HVAC system.

4. 4

   Replace faulty component

   If the fault code re-displays immediately, replace the faulty temperature select potentiometer switch. If the switch is integrated into the panel and cannot be serviced separately, the HVAC control panel/ATC module must be replaced.

5. 5

   Clear codes and return to service

   Clear all fault codes and return the unit to field operation.