On Tuesday, August 13, 2013 9:23:38 AM UTC-4, Peter wrote:
On 8/13/2013 6:19 AM, Frank Thompson wrote:

Thank you, Tim. Your explanation sure helps me understand. What you

are calling the main one is made of plastic. My number one contender

to the source of the problem is that the drain from it is clogged.

HVAC person partially unclogged it on initial visit, but it is my

belief that it is still partially clogged. HVAC person suspects leak

in it but I suspect drain is clogged. Removal of pan is major task

because section of rafter and knee wall supporting beam must be

removed in order to replace it. The cover can be removed w/o

removing section of beam. Is it possible to unclog the drain w/o

removing pan. He has sent water up the drain from the exit of the

drain outside the house and since then situation has improved, but it

is still partially clogged IMHO because some condensate is still

draining into the metal external pan (more into in it than the

internal one).





If water is still leaking from the internal pan into the external pan

after the internal pan's drain has been cleaned, and no one can detect a

crack or corrosion hole in the internal pan,

They can't detect it or investigate it because it appears to be virtually
inaccessible.




it suggests that perhaps

some rafter may have settled (only has to be a degree or two of tilt) so

that cold condensate remains as a shallow puddle at the bottom of the

internal pan, sufficiently cooling the bottom (downward facing) surface

of the internal pan to cause water vapor in the hot, humid attic air to

condense on the bottom surface of the internal pan and fall into the

secondary pan.

The condensate "pan" is normally part of a coil unit that is encased.
The thing is typically insulated. And it's basically inside the
plenum and right next to the coils. Whatever temp it is, it's going
to be with or without a little more or less condensate in the pan.

Now if something has settled so much that the unit is not flat or pitched
slightly toward the drain, then water could be overflowing, but that
would take a lot of pitch in the wrong direction.



You could test that theory by placing a small amount of

water soluble food coloring dye into internal pan and noting whether the

water collecting in the external pan has that color. If the water is

colored, you have drainage/leakage from the internal pan. If the water

is clear, you are seeing atmospheric condensate in the external pan

because of puddling of cold condensate in the internal pan that is not

being drained off properly.

The whole cased coil unit is cold on the inside. It's insulated, or should
be. If it's not insulated, then you can have condensation on the outside
regardless of whether there is 1/4" of extra water or not. The whole
inside is cold, a little more water here or there doesn't matter.