condensation leaking from A/C duct

Just had a new furnace/AC installed, and they extended the ducts to the previously unAC'd addition.(Formerly heated by a wall furnace, now replaced with a gaping hole on an interior wall.) New furnace is 93+, AC is 12 or 13 SEER. It has inline humidifier, but that is turned off. Went downstairs to do laundry, and noticed a puddle under the low point of the duct run, about 4 feet from where it goes through the very expensive hole in the poured foundation wall, into the crawl under the addition. Outside of duct is dry, and the water appears to be coming from a joint in the new duct. It was hot (90+) today, with high humidity, so this is the first real stress test for the unit. The ducts in the crawl, to my dismay, are the 2-layer insulated flex- furnace company said that is all they will install in uninsulated crawls. There is an air return in floor right at the archway to the addition, and that duct is dry. Crawl is dry, as far as I know, but walls are not insulated, and there is no plastic on the dirt, and there are no vent holes to play with. Hasn't rained in several days, and I don't get ponding near foundation, so I'm pretty sure the dirt isn't the cause.
Anybody got any ideas?
Also, while I have your attention- Lots of pronounced air leaks from the box around the A-frame in the furnace stack, around where the access holes for the plastic plugs on the coil are. Is that normal? Should these holes be covered with plugs or aluminum tape or something?
I plan on calling the furnace company Tuesday when they reopen, but I'd like to not look like an idiot when I call....
aem sends....
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ameijers wrote:

improperly installed or plugged up drain. Condensation is normal, but it is supposed to be collected immediately under the evaporation coil and then piped to some place where it won't hurt anything. If you have a 93% furnace the flue on that will drip and that is supposed to also be collected and routed away from the unit. Frequently, but not always, it is run to the sewer. Any way there shouldn't be any condensation dripping from the ducts.
Also there is some question in my mind as to whether it should be able to drip from a duct joint. The joints should be sealed with mastic to prevent air loss. I think that would also impede the dripping. However, at least this way you did get notice that there is something wrong.
Come to think of it, my 93% furnace has a float switch on the drain. If the drain starts backing up the furnace cuts off. I assume the AC also would cut off.
Bill Gill
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