I did not recall that, but it is nonsense. It requires the body to generate the power necessary to cool the body.
But, by the law of entropy, that is impossible.
The body would automatically generate more waste heat than it was capable of removing, because it would be using muscle power to run the pumps.
You have to dump the waste heat somehow.
Maybe that escaped my memory as well. Was there some sort of magic material to dump the heat to the atmosphere? Did the book mention the temperature?
I am sure others will check my logic here.
All a stillsuit was supposed to do was preserve as much moisture from escaping as it could. It was not anywhere near 100% efficient even under the best conditions. It required the wearer to breathe in thru the nose and out thru the mouth. Urine and fecal matter was collected in side leg pockets and moisture recycled. Even with a good Fremen-made stillsuit, a person could only last about two weeks in the open desert of Dune with no replenishment of water supply........................