EDIT For clarity please see the answer from Richard Crowley. Essentially I want to achieve his circuit with an automatic switch via a pre-set max temp. Really appreciate all the help so far. Thankyou all ******
So I want to vent my home server room as it is getting toasty. I have been running a couple of fans rigged into a homemade vent system to allow airflow. I use a voltage regulator to control fan speed and they have been fine but now cant handle the midday heat- fine rest of time.
What I want to do is keep them wired as they are but add in another power loop with a higher voltage wired through a temp activated switch. Unless I've messed my logic this should allow current cooling for most of the time but when it gets toasty the switch should trip and the fans will get a power boost= more CFM= more cooling till temp drops then back to normal again.
Will this work? thanks