I am creating a closed loop gycol heating/cooling system for beer fermentation and lagering. The system uses a ITC-1000 temperature controller and two power supplies to feed a heating circuit and a cooling circuit with peltier devices attached to a water block and pump. See below:
I need to have a single pump(to pump gycol) and fan(to cool internal components) powered when either circuit is active. The circuits will not be active at the same time. How do I wire these to not create a feedback loop and not supply power to both circuits? Do I need to use diodes, and if so how/where do I wire them?