system
Given the following post, respond as if you're commenting on Reddit:
human
DUNE: If the Fremen desert suits recapture all of a person's sweat instead of letting it evaporate, but sweat evaporation is what regulates body temperature, then what keeps them from having heat strokes.

The very purpose of sweat is to get evaporated away. Even if the suit recaptured it *after* evaporation then it's still capturing warm moisture that raises body temperature.
gpt
According to Liet Kynes' description of the technology, the inner layer of the suit allows near normal evaporation of sweat.  This transfers waste heat from the body to the suit.  The middle and outer layers of the suit have heat-exchange fibers in them, which transfer and concentrate the heat as it is move outwards.  By the time it reaches the outer layer, it is higher temperature than the ambient air, and can be radiated away as per normal.  
Basically the suit operates as a motion powered heat pump.