Plenum Box In Attic Leaking Water

If it is just leaking a brush on mastic sealant works well.

Plenum box in attic leaking water.

If it s not able to pump the excess out check to make sure the pump is getting power. The first thing you should look into is the condenser pump as it could be broke. Excessive air velocity through the evaporator coil could cause the condensation to blow over the pan and leak out of the plenum. As an added measure fiberglass tape bedded in the mastic will help strengthen that joint against expansion and contraction.

To test if it is the condenser pump you can pour water into the condenser pan if it works the excess should be pumped out properly. As soon as you discover a leak be sure to turn off your air conditioner. Because the plenum is where the greatest air pressure differential is found it is therefore the 1 place to seal to save energy and cash. Seal all seams and where the ducts connect.

If the sheet metal is ruptured it has to be placed back together and reinforced. Any leaking or pooling water around an indoor ac unit should be attended to right away. Your plenum will typically be located in an unheated area of the house such as the attic or garage. If the metal anywhere on the ductwork is exposed to ambient air from the hot attic then it will cause the ductwork to sweat leak and cause damage in your attic.

But this is an uncommon problem. I find it interesting that the problem started after you moved the duct. There are a few reasons why water would leak from the plenum.