Should I open my AC register in the basement to help with condensation?
My recommendation would be to run a de-humidifier in the house to control the excess humidity. If you do not want the noise in the living space as I did not then I would put the de-humidifier in the basement. You should open 2 registers in the basement and have at least 2 floor level return grills to circulate air in the basement. Set the de-humidifier at a comfortable level and now you can control the excess humidity. This is what I did and it works great. My de-humidifier is a 70 pint model bought at the 1 of the big box stores.