On Thu, 12 Jul 2007 00:20:23 GMT, M Q
wrote:

Art wrote:

That sounds normal. A system that is too large for a house will turn on,
cool the house quickly and turn off quickly. Every turn on and turn off
shortens the life time of an ac. In a perfect world it would be sized to
run forever keeping the house at the right temperature and never turn off.
Of course the outside temperature is always changing so that a perfectly
sized ac system is impossible to design. That is why they have multistage
systems. ...

Actually, while you are right that the reason for multistage systems
is so that the AC does not turn on and off as often, the major reason
that this cycling is undesirable is not AC lifetime, but energy efficiency
and humidity control.

When the AC turns on, you are spending energy for a while cooling down
you evaporator, ducts, etc. before you get to full efficiency.

Your reason below certainly makes sense, but I don't think this one
actually does so much.

When the evaportator, ducts etc. warm up between AC cycles, they are
sucking in heat from their surroundings. This cools the house, and
keeps the surroundings from warming the air when the AC is on.

And at he same time, the condenser is cooling down, which should make
the condenser more efficient until it warms up again.

When you
turn on and turn off, you are blowing previously condensed moisture back
into your home.

Yes, but I'm sure you mean some of it. Not the stuff that has drained
from the pan and gone into the sump or the condensate pump.