Bunk Heater

I have a 2006 379 Pete with a separate bunk heater unit. I am only getting cold air to blow. If I unhook the wire from the temperature sensor in the duct work, the heater goes to full blast hot. Fan speed works on 1234 just fine. I have replaced the actuator, temp sensor, and reastate (hot/cold) knob up on the bunk control panel. I am at a loss for things to try next to try and fix this problem. I think the only other part is the $550 wiring harness/module that is on top of the heater unit with all the wire pigtails attached to it.
Any experience or advice is appreciated.

 

I have not found any yet. I checked all fuses in panel by clutch pedal.

 

All the wires go into a module for the whole wiring harness. This is the only part I have not replaced yet cuz it is $550. Peterbilt tells me they have never sold one, so I hate to buy one just to try it, but im running out of options. Luckily I am in my shop and have some time, cuz this is getting frustrating. I just want to find the issue, so i can get the bed back together and get on to the next project.