Issue with entering piecewise function into rkfixed?

Hello,

I am trying to solve a series of two first order ODEs, the ODEs are a function of time but also include a piecewise temperature component that varies with time. I believed at first this is what was breaking the solver but when I make the temperature constant the solver remains broken. Can anyone see where my mistake is? I am thinking it is most likely the constants and/or initial conditions. 

Thanks for any help that can be provided.