This looks like either a control head or the ac BCM issue. It needs to be checked with a DRB scan tool.
The ATC system can be diagnosed two ways. The DRB II scan tool can be used or the vehicle's own control head display may be used. If the DRB II scan tool is to be used, refer to the Diagnostic Charts later in this section.
The control head can only be placed into the diagnostic mode while the engine is running and the vehicle is not moving. Set the control to a 75°F. Setting (so there is no confusion with 23-36 Diagnostic Trouble Codes).
Entering Self-Diagnostic Mode
To place the system into it's diagnostic mode, press and hold the floor, mix and defrost buttons (at the same time). The ATC head display will begin to blink. When the control head display begins to blink release the floor, mix and defrost buttons. Once the control head enters its diagnostic mode, the display on the control head will continue to blink until it completes its tests and calibrations. Then it will display any diagnostic trouble codes that are present in the body controller (which relate to ATC operation) on the control head display. If there are no diagnostic trouble codes the system will return to its normal operation as indicated by temperature display.
Diagnostic trouble codes related to the ATC system will appear on the display in numerical form. The diagnostic trouble codes are stored in the body controller and diagnostic trouble code numbers can range between 23 and 36. The control head can only show one diagnostic trouble code at a time. Under certain circumstances more than one diagnostic trouble code could be in the memory. To scroll through any additional diagnostic trouble codes, press the panel button.
If diagnostic trouble codes are found, refer to the Diagnostic Charts for repair procedures.
IMPORTANT NOTE: The control head cannot display all diagnostic trouble codes stored with in the body controller. There may be other diagnostic trouble codes in the body controller not related to the ATC system. These codes can only be found using the DRB II scan tool.
Images (Click to enlarge)
Wednesday, June 6th, 2018 AT 8:25 PM