It took awhile, but I finally figured out that our condensation problem is due to poor ventilation in the crawl space. One short side of the house has two vents. The front (long side) has only one, as does the back. The attached garage was converted into a bedroom or recreation room. It is on slab, so there is no vent on that short side. The entrance to the crawl space is a 3 x 2 opening with a wooden cover. Rainwater goes into trench drains under the crawl space and out through a sump to a rain garden I just installed to alleviate a mud hole.
The problem is really everywhere, because there is a mold problem in most of the registers. The most serious problem in under the living room window on the long side of the house. Condensation is on the carpet three or four feet from the register. It is difficult to get an accurate measurement, because it migrates to apparent low spots.
Someone decided to route the heat and AC under the house by apparently one duct, but I'm not sure. This may have been to take care of the poor ventilation. However my energy analysis shows us as way above similar houses for electrical, but we have energy saving bulbs almost everywhere, excluding three closets.
What is the least expensive fix? We are retired and on a fixed income.