That speed adjust device is a piece of trash. Either that or I got a bad one. I initially had it on my Zalman and it kept the fan from running at max speed. Also sometimes the fan would stop spinning completely and the fan controller's controls would reverse and I'd have to turn it the other way to turn the fan on. And then the RPMs would be very low on max. So basically, I ripped that piece of crap off and threw it in my closet somewhere. I get better temps and no bull without it.