"Joseph Meehan" wrote in message
...
Because it is more than 78º in side and to keep it there it needs to
run. You could open up windows and run a fan to get it below 78º but that
would let in so much moisture, the A/C would run longer to get rid of that
extra moisture than it now runs to keep it down to 78º.

Actually, that's not completely correct.

If the homeowner has a combination thermostat/humidistat that will turn on
the A/C to lower humidity, you make an excellent point. In other words,
most current Tstats have no way to measure the %RH in the house.

Otherwise, the Tstat is just reading the heat level in the house.