> because our office fridge kept freezing my carrots.

That sounds like a goal to me

That's quite nice! You may wish to look into implementing a PID controller, so as to avoid overshoot (your carrots become too thawed initially) and unnecessary oscillation about the setpoint (meaning you are wasting energy on cooling and heating cycles that in the end cancel each other out, where you could have kept the temperature nearly constant during that time). I loved juicing carrots so much my face turned orange from the beta-carotene.