Hi,
Then see if the resistor/voltage follows Ohm Law and what speed the fan turns at.
Everything follows Ohms law, of course, but fans are inductive and mechanical, so won't follow with a linear relationship with voltage, if that's what you meant.
nixter <-
I wonder why everybody and his uncle (at least if said uncle is very young) have this strange idea, that they can control a fan better with manual control than with a thermal sensor and my guess is, that it must be a lust for buttons making them feel in control or something, but let me assure you - electronics is far better at regulating temperature than us humans that, over a year may claim it cold at so diverse temperatures as eg. -20°C in the winter and +20° in the summer.
That aside, even with manual control, you need something more than a high value potentiometer.
A rheostat (which is in reality just a high power potentiometer) is the low tech and quite poor solution - Go get rheostats of around 60 Ohm and at least 2W. Mount them, not as potentiometers, but as variable resistor in series with the fans.
60 Ohm makes sure you can cover their entire speed range (one should be around 40 Ohm and the other around 50 Ohm, but rheostats doesn't come in every size, so anything available to you which is between roughly 55 Ohm and 65 Ohm will have to do.
The sensible way (if that word could be used here), would be to use regular pots and a simple PWM circuit for each fan, as that would be easier to control and won't waste power in heating up a rheostat. With a bit of savvy, each could be tailored to cover the speed range from 0 to max. over the range of the potentiometer.
A good fan circuit speeds up the fans to full power for a few seconds at start, to make sure the bearings/bushings won't set. With manual control, do this at least every tenth time you use the fans by cranking it up all the way for a short moment.
