I have lived in this house since it was new, 20 years ago. This past
week, during the late afternoon, I would get condensation coming from the
air outlet closest to the air handler and right after the coil. I
remember reading on this group that this is probably caused by icing of
the coil. remembering that low air movement across the coil could cause
this, I changed the filter and this time used a filter that would allow
more flow ( I had one of those super duper ones that wouldn't let any
pollen through). For the next day or so, that seemed to fix the problem.
Now today, It has started again. I turned the AC off for about an hour,
then turned it back on and no more condensation dripping from the outlet.
I know, however, that it will probably return in another couple of hours.
It is presently 100 degrees outside. The humidity is about 40%. Inside
the temp is 77 degrees with a humidity of about 33%.

This is the situation. The compressor is out side. Everything else is
inside in the attic. Over the life of the AC, the filters have NOT be
changed out on a regular basis. For the first 15 years or so, I used the
el-chepo filters. Usually, when I did remember to change them, they were
clogged up with dust. Last year I had someone come out to do a checkup.
This was the first time in about 10 years. He measured the flow from the
vents and used the gauges (I have no idea what the measurements were but
he said the readings all looked good). He also checked the temp of the
air coming out of the vents. All was good for the unit I had. He of
course tried to sell me a new high effency unit, but when we finished
talking, the payback would be after I was dead.

So now I'm thinking that one of two things is wrong. Either the coil is
clogged up and won't allow enough air to flow through the coil and it
therefore freezes up, or the freon level is low(?). There seems to be
good air flow coming from the vents and the air is cool, but can the air
get around the coil? Or is it possible that some of the coil is clogged
and that's where the ice starts to form, and then it just gets worse from
there?

I know I'm going to have to call an AC guy out, but I'd like to have an
idea of what else the problem could be.

Thanks.

Dave