Assuming the thumb wheels are OK, place a long screw driver from your ear to the top of each of the 2 solenoid things that are just in front of the battery and electronics box.
These control the flow of hot water into each side.
With the A/C on and running, see if you can hear a clicking from one of them, and not the other.
If you do, then there's probably an issue with the panel module, if not then one of them could have it's valve stuck open.
There's a DIY on here somewhere about replacing the actuator valve stem with a pop rivet, believe it or not !!!!!