HVAC is not working why?

Additional information:

(I'll try to record video when behavior changes again)

Start truck - system turns on (backlights lit up, and amber control lights on buttons responsive to changes).
Driving down road - working, then stopped out of nowhere.

Get call on cell - system kicks on (blowing air/control amber light on)
*I disconnected battery yesterday for 2 hours/stereo was set to use SYNC for Bluetooth handsfree by default* (Didn't answer call). Display panel on top rebooted at this time as well.

Stopped working shortly after starting with Bluetooth kick in butt.

Stop truck, park - still not working, sit in truck for 20 seconds (seat began to slide back - ez exit). Then air controls kick on again (amber lights on).

*Is it SYNC related?

This might help - Video link:
https://photos.app.goo.gl/kH2C9k3dkze3Nydv5

Thanks for the schematics and documentation. I ran FORscan on it last night and reset the APIM, FDIM and BCM. It throws errors about communication to the FDIM. (Code: U0164 - Lost Communication With HVAC Control Module) and the APIM has this code: (Code: U0256 - Lost Communication With Front Controls Interface Module A).
Is the APIM a swappable part from another salvage truck?

Not sure I can run the tests in FORscan. I connected and cleared all codes (DTCs would not fully clear). What is in logs is persistent.
===TPM DTC None===
Successful DTC reading, no error codes found

Module: Tire Pressure Monitor

===END TPM DTC None===

===GPSM DTC None===
Successful DTC reading, no error codes found

Module: Global Positioning System Module

===END GPSM DTC None===

===FDIM DTC None===
Successful DTC reading, no error codes found

Module: Front Display Interface Module

===END FDIM DTC None===

===PCM DTC None===
Successful DTC reading, no error codes found

Module: Powertrain Control Module

===END PCM DTC None===

===OBDII DTC None===
Successful DTC reading, no error codes found

Module: On Board Diagnostic II

===END OBDII DTC None===

===APIM DTC U0256:00-2B===
Code: U0256 - Lost Communication With Front Controls Interface Module A

Status:
- DTC Present at Time of Request
- Malfunction Indicator Lamp is Off for this DTC

Module: Accessory Protocol Interface Module

===END APIM DTC U0256:00-2B===

===OCS DTC None===
Successful DTC reading, no error codes found

Module: Occupant Classification System Module

===END OCS DTC None===

===TCCM DTC None===
Successful DTC reading, no error codes found

Module: Transfer Case Control Module

===END TCCM DTC None===

===RCM DTC None===
Successful DTC reading, no error codes found

Module: Restraint Control Module

===END RCM DTC None===

===PAM DTC None===
Successful DTC reading, no error codes found

Module: Parking Aid Module

===END PAM DTC None===

===PSCM DTC C1B00:62-0B===
Code: C1B00 - Steering Angle Sensor

Additional Fault Symptom:
- Signal Compare Failure

Status:
- DTC Present at Time of Request
- Malfunction Indicator Lamp is Off for this DTC

Module: Power Steering Control Module

Freeze Frame :
-MOD_SUP_V: 11.75 V - Module Supply Voltage
-PWR_MODE_KEY: Accessory - Power Mode Key State
-PWR_MODE_QF: Eval in Progress - Power Mode Quality Factor
-SW_ANGLE: 0.00 ° - Steering Wheel Angle
===END PSCM DTC C1B00:62-0B===

===BdyCM DTC B10F1:14-0A===
Code: B10F1 - Key In Switch

Additional Fault Symptom:
- Circuit Short To Ground Or Open

Status:
- DTC Present at Time of Request
- Malfunction Indicator Lamp is Off for this DTC

Module: Body Control Module

===END BdyCM DTC B10F1:14-0A===

===SCCM DTC None===
Successful DTC reading, no error codes found

Module: Steering Column Control Module

===END SCCM DTC None===

===IPC DTC None===
Successful DTC reading, no error codes found

Module: Instrument Panel Control Module

===END IPC DTC None===

===ABS DTC None===
Successful DTC reading, no error codes found

Module: Antilock braking system

===END ABS DTC None===

I also ran live scan on FDIM.(See pic)

For replacement parts. I replaced the climate controls BL3T-18C612-DF, last October (per eBay purchase). This unit worked well for a couple months then began to bug out. Rarely, progressively getting worse.
My stereo completely quit working, no audio (was 6disc).I swapped w/ the JVC in the video, I have iDataLink and setup with SYNC integration. (This was done June 2020)

When I did all my test/scans tonight the HVAC was working the entire time, I might have to wait for it to fail to see where the problem is?

Cool, I'll get that done this weekend and report back. Thank you sir!

Finally got by the parts store and they tested alternator and battery. Battery was bad. Replaced, unit is working, but it was working before. The issue was intermittent. I do believe this to be the cause though, I noticed when the truck fired up after replacing the battery the HVAC controls were off. I thought, great still broke. But when I hit power, it powered up. This hasn't been the case since this issue started. I never really had 'control' of power to the unit it seemed like. So that is a difference I do know that is positive. I will continue to monitor, but overall I greatly appreciate your help and will mark this fixed. If it comes back to haunt me I'll jump back on this thread. Thanks so much!