What are these wires /sensors above my APU display panel?

The parameters can be adjusted through programming by a Thermo King dealer. Heres a link for a service manual (PDF).

 

That wire is your temperature probe. Senses air temp. Looks like your control box sides have sleeper sides against the box so the sensor probe had to be routed out of the panel front. The lack of control can be either a problem with the control box or the temp sensor probe just doesn't have enough air around it for it to notice any change in cab temp. The heater is not part of a TRI Pac. It is a seperate unit put out by Espar that can be tied into the control panel of the TRI Pac. It is possible that since you have 2 sensors that one is for the TRI Pac's air conditioner (part of your TRI Pac) and the other sensor is for the Espar heater. I'm going to bet the the only control you have for the heater is On/Off and it is not wired into the control temp. Take the truck to a ThermoKing dealer and see what they can tell you about the wiring. There are options that will make it more usable.

 

there are two sensor settings you can have on your APU.

One is for the Espar. You pretty much NEED that one.

The other is an ambient air temp sensor. If you have two sensors, it's likely that is turned on as well.

Without going in and seeing the HID settings, I won't speculate past that.

 

They just send signals to a digital potentiometer on the motherboard under your bunk. The problem can be anything.