You have humidity infiltration.

You have to understand it, its location, and reasonable remediation options to reduce it.

Your home is on crawl space or slab?

IMO

Basements with walls which are below grade are going to have a higher humidity level than the floors above grade. Some of that humidity is coming up through the floor to the first level.

The AC needs to run for long periods of time to dry out the basement and first floor. Have you tried using a dehumdifier in the basement? It may allow you to maintain the 50% humidity level without having the run the temperature down to 69 degrees.

The home has a basement....on a concrete slab.....with block walls. The home was built....1950? Even, now.....the temperature is comfortable.....71 or 72......feels okay......the a/c hasn't been running......but the humidity is around 65% on the first floor......it feels kind of muggy......see my problem.......the temp is good......how could I possibly run the a/c with the temp this low.......it would only run a few minutes......unless i set the thermostat at 65 degrees! Help!

Read carefully!! Use a dehumidifier in the basement!!

Almost forgot.....I am using a separate portable dehumidifier in the basement......it fills up each day.

I want to thank....you all.....for your very helpful advice/comments

Are you able to keep up with emptying out the dehumidifier? Does the dehumidifier run constantly? It would be best to either hook up a drain or add a condensate pump. You may also need a bigger dehumidifier.

Make certain blower speed is no more than 400 CFMs/ton, possibly even one step lower. Also blower fan at thermostat should be set to auto, not fan on. Both should help dehumidification.

IMO

This post was edited by tigerdunes on Fri, Jul 12, 13 at 13:02