I have two AC units that cool the house fine when they are running throughout the day. At night when it is cooler, I have one that comes on for one a minute or less and then turns off. I have also noticed very hot, moist air coming from the floor vents around the house with the air handler off. This is new, or I haven't noticed it before. There is a moist, mildew odor with the hot air as well. What causes this and what do I need to do to correct this?