AC fan wont run on auto mode

There's no owner's manual for installing it into an RV, but I did follow the instructions from others who have done it before me - with success. I'm really hoping it's not the t-stat itself since I am unlikely to get it replaced with the modifications I have made to it - everything I did was to the plastic housing, but I wouldn't out them past saying I somehow damaged the electronics in the process. It's been installed for less than 2 months, but now that I think of it I think the only way I tested the AC was with the fan switch set manually, so I don't know that it ever worked right.

I'll mess with it some more on my day off tomorrow. I was hoping it was going to be an easy answer saying I did something dumb, but I guess it's not that simple! ;)