If your crawlspace floods, regardless of the season, the vents should be opened to help dry out the crawlspace. When the humidity levels in the crawlspace are higher than the humidity levels outside the crawlspace, the vents should be open.
A sudden moisture change at the windows can be caused by various conditions inside the home. It is extremely important to drain water away from the home for several reasons.
Ensure gutters and downspouts are not clogged and are draining at least six feet away from the foundation. If the grading of the yard looks like it is not sloped to carry surface water away from the house, it will need to be regraded. Have someone check the roof and exterior walls for any obvious signs of water entry and repair if needed.
As for the crawlspace, make sure you have a good vapor barrier (plastic sheeting) covering all of the exposed ground inside the crawlspace. The vapor barrier prevents moisture from the ground getting into the crawlspace and home.
Your air conditioner is a dehumidifier and that’s why most moisture problems do not appear in the summer months. Adding a dehumidifier to the basement will help to control the indoor humidity problems.