So on this truck, All of the user controls (buttons & ***** and LED Indicators) will be non-responsive. Normally pressing the Power Button will light up some of the Amber LED's to indicate power and the mode it's in, However this is completely dead (most of the time at least). The HVAC climate control module has already been replaced as well as the multi conductor harness. Intermittently, the climate control will light up and actually work and the blower fan will come on as well as the Compressor, and cold air will blow! However, without touching any wires, it will shut off on it's own and will "decide" when it wants to come back on again, of course not when you want it to. Tried replacing the 5A fuse and blower motor relay (just for kicks) and I though that fixed it, but now it's doing the same thing again. The HVAC module is getting power and ground but I'm wondering if it can be a CAN BUS issue as it seems this HVAC module must communicate with the PCM (which controls the relay for the A/C Clutch). I've attached the related diagrams for reference. It would seem the problem is just the HVAC module (Climate control Assy.), but I just wouldn't imagine it to go bad that quick as it was replaced a few months back.

 

Just to clarify, as it is now when it stops working, do you still have the switch led lit up on the climate control or do you loose that to?
If you loose the switch light, i think I would check the g203? ground and be sure it's clean and tight.
I would also look at the connectors involved in this circuit going to the BCM.
If the switch light stays on, to me it would say you have power to the climate control panel and yes you may have a communication issue.
As these trucks age, poor connections and broken wires do show up.

 

Possibly the blower motor resistor?

 

So, when it stops working, I DO loose LED indicators on the climate control. When probing with a smart probe, both grounds are present at the module even when it's not working. Also, the module wasn't replaced a couple months ago, but rather a week ago (got confused with another truck).
On Friday, connected to the truck with IDS and ran a test on Climate control module (of course it was working at the moment) and it pulled up (2) DTC's. One wasn't active (B10AF: blower fan relay circuit open) and the other one was active (U2100: initial config not complete).
So at the moment it worked each time I tried on Friday, so thinking on Monday to put it all back together and have the driver use the truck and report back if it acts up again. I'm afraid the "gremlin" will reappear, so want to make sure all the essential connections to/from the climate control module that relate to the module LED's working are good as relay output and such is easy to troubleshoot..

 

I would pull the C2280A connector at the BCM and be sure it looks clean etc. That looks to me where you would be getting power to the module. Maybe its loose there.
These pictures are from my 2013 manual.
Good luck.

 

I had exactly the same issue (intermittent climate control) and you are right it is coming from the C2280A connector. Unplug/Plug solve the issue temporary but in my case the underlying problem is a windshield tiny leak that drip down creating moisture around the BCM.
Have fun.
Mic

 

Yes you can get some quirky operation with water intrusion issues at the BCM. Ive also seen a control head blanking out from a network short caused by a bad blower speed controller, but you have manual AC according to your schematic so that should be ruled out.

 

Especially if you have the XM antenna leaking right above it on the roof, like mine did.