heating an object, then cool and then reheat , step function

Hello.
I wanted to study the behavior of the von Mises stress that will developed in a spheroidal object subjected to the following conditions.

time: 0 --> 3 mins ----- heating at constant temperature 45 C
time: 3 --> 4 mins ----- cooling at constant 15 C
time: 4 -->10 mins ----- reheating at 45 C

I am using version 4.0a for the coupled thermal diffusion and structural mechanics to study the temperature distribution and mechanical deformation. But I do not have an idea on how to put up the step function on the temperature settings on the conditions that I wanted to.

The step function in the under the Global Definitions seems do not have temperature settings.
Is there somebody out there who can give me some hints on how to properly do this.

I'll appreciate much for your help.
Thank you.

Jonathan