[RobsGreen]

I have updated the setup slightly since then, I added a speed control and timer. This is how it works.

The timer is the very first thing inline, I can turn it to auto or on. For the first part of my grow (in my smaller cab) I didn't need the fan to run all the time so I put a thermostat inline. Power was alway on but it was up to the thermostat to kick a relay and feed power to the fan. I wired it on the cool side of the thermostat not the heat part. This way when temps got to lets say 76f the thermo would kick the relay and allow the fan to turn on until it got down to 75f. Just like your furnace but backwards. But then later in flowering I needed the fan to cut in every 15 minutes or the humidity got to high so thats when the timer came into play. I would set the thermostat down to say 65f, a temp that would never happen, that would always keep the relay kicked, they when the timer came on power would get to the fan. Hope all that makes sense. Here's an updated diagram, not much but might help.