Temperature sensitive vents are vent covers that go into the crawlspace vent openings designed to open when temperature is high (typically around 70 degrees F) and close when temperature is low (typically around 40 degrees F).
These temperature sensitive vents are effective in aiding to contain temperature levels in the crawlspace with the goal of saving energy and especially keeping pipes from freezing in extreme cold temperatures. For some homes, that may be very important. However, they are not an effective tool for moisture control.
As has been explained in the Moisture Section of the website, the air is often at its driest outside when it is cooler and at its wettest when it hotter outside. These temperature sensitive vents will open during the wetter times and close during the drier times.