Air Conditioning - Condensation Leaking from the Plenum !

My original problem was that the master bedroom was not cooling equally with the rest of the rooms on the same floor. We have two units for a three story home. One unit cools the down stairs and the second cools the second floor and a loft area. I called a service tech to come and inspect the second floor system and give me some advice on how to cool the master bedroom. First tech said I needed to install a third system due to the construction of the house and the way the duct work had been installed. Second tech said to change the location of the duct that was being used to cool the bedroom. Tech advised me to remove the duct from the side of the plenum and attach it to the front of the plenum, thus forcing more air to the bedroom. So, I relocated the duct from the side of the plenum to the front and sealed the original and new location of the duct. Last night the room was cooler and all was well. However, today I was working in a room below the air handler and water started pouring from the ceiling. I went to the air handler and discovered water under the plenum and leaking from the plenum onto the ceiling. Why did this happen? Is there too much cool air being forced down the duct and not being able to get through the register?

Dont see why this just started. Is new out let near the coil?? But first have you checked the drain line is it clean ??? You didnt drop anything on the coil?? or down in to the drain pan. Take a shop vac and suck and blow on the drain line.
ED;)

There are a few reasons why water would leak from the plenum. I find it interesting that the problem started after you moved the duct. Excessive air velocity through the evaporator coil could cause the condensation to blow over the pan and leak out of the plenum. But this is an uncommon problem.

This problem typically occurs if the fan is oversized or if the evaporator coil is dirty. If you have had a filter in the unit continuously since it was new then it is unlikely that the coil is dirty.

First I would check the filter. This is the number one cause of water leakage. A dirty filter will cause the coil to ice up. Condensate pans aren't usually designed to contain the water from an iced up coil.

Second I would check the condensate drain pipe for blockage. This is also a common problem. The best way to unplug a drain pipe is with compressed air. Another way is with your garden hose. Though this can be messy if your not careful.

If you have an older unit I have actually seen condensate pans develop cracks. Inspect the drain pipe also and make sure it is not cracked or leaking. I have seen drain pipes come apart just by bumping into them.

If the problem persists then I recommend having a technician check it out. If the condensate is blowing over the pan he may be able to slow the fan down. If the pan is cracked he may be able to seal it. Odds are he'll just sell you a new evaporator. Sealing a pan can be difficult and doesn't always work. The unit may also be undercharged. This can cause a coil to ice up. A technician will check this also.

Thanks for the advice and direction this site is great.
Okay here's what I found. Upon opening up the panels to the cooling core I discovered that the entire air handling unit was leaning towards the plenum and not allowing the water to drain from the pan into the drain line. Instead the water was flowing out of the drain pan into the plenum and the out of the plenum onto the ceiling. Our unit is in the attic and sits horizontal. I used a small car jack and a 1 X 6 to raise the area of the cooling core and plenum then placed a 4 X 6 under the core area to keep it level. This allows the condensation to drain through the drain line. Replaced the panels and sealed the area with tape and mastic. I am concerned about the build up of mildew from the water draining into the plenum. Should I remove some duct work and spray some disinfect in the plenum or not worry?

Instead the water was flowing out of the drain pan into the plenum and the out of the plenum onto the ceiling. Our unit is in the attic and sits horizontal. Dont know where you are . But most codes call for a overflow pan under the AC unit up in the attic. This has to have a drain pipe to the outside of the home. They also call for a overflow cut off switch now on the unit. They have one that will go right into the P trap on the unit. You might look into it

ED;)