Air Conditioning - Lenox Air handler Sweating Badly

We just had 2 new lennox 20 SEER type units installed here in Florida. The 2 ton works perfectly. The three ton keeps sweating so much inside the cabinet, it drips into the overflow fan. The installers have been back many times. It's a 3 ton 20 SEER unit mounted in the attic space. All pressures have been checked OK. The backpresure is less than 0.2 and the supply pressure measures 0.2 inches of water. They added a second return duct, so now we have 2, 18"x24" return filters a few feet from the intake on the air handler. They sealed up the cabinet with tape and sticky foam tape. When you open the air handler, the bottom inside is wet. You can also see condensation on the back wall where the electronics is located. The drains are all working fine. It just appears that the inside of this unit sweats and they can't fix it. After 2 months, you can see rust on the 50 amp circuit breaker terminals. Maybe the whole cabinet needs to be insulated??? Does anyone out there have any ideas? It's a real reputable company, they are trying, but I think they are stumped.

Have they lowered the fan speed?

No. They said they measured the CFM and it is OK. I did not actually see them measure air flow.

What is the RH in the home?

The RH is 52%. The thermostat reads out RH. The speed setting is at 980 cfm for first stage cooling and 1400 cfm at second stage cooling. (First stage is 70% of second stage cooling.)
There are two 14" inlet ducts from the filters. On the supply side there are four 8" ducts (they start as two 12" ducts off the supply plenum and then split into the 8" ducts, one 3", and two 6" ducts.

Id lower the fan speed and see if that helps.

Is there a reason for lowering the fan speed? Why would lowering the fan speed cause less condensation inside the air handler cabinet?

Increasing the fan speed would dry out the air handler (wouldn't be as cold). It would also decrease the humidity removal .

The system is working in PRECISION MODE and it is set at 50% humidity. Sometimes the fan runs slowly if it is in dehumidify mode and it goes to a medium speed for regular cooling. When it goes to second stage, the fan speed ramps up to maximum setting of 1400 cfm.

Is the moisture showing up on the foil covering of the insulation, outside of the cabinet or just the bottom of the unit?

The unit is mounted horizontally. The moisture/water is in the bottom under the fan. The air comes in on the left and flows accross the evaporator. Then there is the fan and then the supply plenum. The moisture/water collects under the fan. There is evidance of condensation in the electronics compartment. The water actually puddles inside the cabinet under the fan and then leaks out at the cabinet seam under the fan assembly into the emergency overflow pan under the entire air handler.

If I were in your situation the first thing I would do is ask the installing contractor to bring in the factory tech support rep because he is not able to figure it out. Beyond that if I was stuck without help and wanted to try to figure it out I would change some things to see what impact they might make. First thing I would try is to reset the internal controls to get the fan to run close to 1400 CFM constantly for a day or two then see if the cabinet dries out then if it does you can surmise that reduced air flow is causing this problem and start making decisions from there. And because you have another system that is not having the problem you have a test control to use to see what differences there are (is one ducted significantly different, are the controls set up differently, etc.)

My installer is meeting with the Lenox rep on Monday. The fan is set at 1400 now. I think it's best to wait until they see what the next step should be. One of my big concerns is that the entire bottom inside is wet and all the components in the air handler are wet. Mold will start to form. Like I mentioned already, the 50 amp breaker failed after one year. It was a corroded mess on the inside of the breaker.(I took it apart.) The new breaker is only a few months old and is showing signs of rust on the terminals. I'm starting to think that I need additional ducts on the supply side. They said the supply side static pressure is 0.2" of water.

Let's back up a little bit. You said both of your drains are working, that includes primary and secondary. However, If your primary drain wroks, you should not see water under the fan, if the primary does not work, or for some reason the water did not go into the primary drain, but because your secondary drain works, the water should be drained out from the secondary drain pipe, which means you should not see water puddles in your pan, or under your fan. .......... I would double check both drains to make sure they are working.

The main drain under the evaporator is working perfectly. When the air handler is open, you can see a small amount of water in the fiberglass drain, not much, what is expected according to the installer company. The water collects in the air handler enclosure under the fan. It drips out into the emergency at a very small rate. actually, you have to run your hand over the underside of the air handler and your hand comes out wet. It does not puddle in the emergency overflow pan. The big question is why this water is collecting in the air handler cabinet.

Yeah if you start looking at all theses other things you can get away from the real issue. You know a plugged up drain is not going to cause breaker corrosion you obviously have metal surfaces whose temperatures are below dewpoint. If you have the factory guy coming and you are at full air volume you have done all you can. That is why I was talking to you about the similar system so you could compare the installation. I would just about bet there is not enough ductwork on this thing and when the factory guy walks in I guarantee you that will be the first thing he looks at.

Like I mentioned above, they added 100% more return ductwork. I have two 18 x24 returns. This has been going on for a while, so I hope they can fix it. Does anyone have a feel if I have enough supply ducts? See above for how many and the sizes.

i wonder why they are trying to flow 1400 cfm on a 3 ton should be 1200 also i think they are bsing about the static pressure .02 return and .02 supply = .o4 total that is one hell of a duct system . what does the trap on the drain line look like maybe not deep enough .

The supply plenum static pressure is 0.2, not 0.02
As an Engineer, I have always put a zero in front of a decimal point so there is no confusion, sorry.

The return went from 1" of water down to 0.4" after the new return intake was added.

The drain line trap has water in it and is dripping when the unit is on.

What does the extra cfm cause?

has the tech or yourself checked the temp change across the coil ? .to much air flow causes poor dehumidification. if the duct system is to small the air velocity will be high causing condensate to blow off the evaporator coil

I will ask them to measure it. That sounds like something that could be causing the problem.

The Lennox tech rep suggested that the condensation INSIDE the air handler may be due to a very humid attic. The test will be to seal up the soffit vents in the attic over the garage. This attic is connected/open to the main house attic. I am leary of this idea. He says that a very humid attic can cause this problem. The air handler is super sealed up at every pipe in/out and has tape over all seams. I'm not sure how or if any of the attic air could even get into the system. The attic is accessed via a drop down stairway. I have noticed that when the air handler spools up, you can feel a slight breeze coming up through the hole where the stairs are located. There is no apparent leak in the system. I'm still thinking I need insulation on the outside of the air handler and the in and out plenums.

Blocking up the soffit vents is not OK with me. I just added a 1500cfm attic vent fan that comes on at 105 degrees F and off at 100 degrees. maybe this will help keep the temp down around the air handler and reduce the possibility of sweating inside the unit.:D

I took out the attic fan since I was told it would make things worst.
Today, we decided NOT to plug up the soffit vents. We read the manual from Lenox. The manual is clear on the following for a HORIZONTAL RIGHT-HAND DISCHARGE:
The top down-flow rail must be removed for all applications and the bottom down-flow rail has to be removed when the unit is in a high humidity location, which it is. These are metal 22"x1"x1" metal angle pieces. My guess is that they do something when the unit is mounted upright. My guess is that they were forming condensation and dripping to the bottom of the air handler and leaking out the middle bottom seam. They also set the blower speed from 1545 to 1400 cfm for second stage cooling. First stage is now set for 980 cfm for a 3 ton unit. Second stage is 1400 cfm. If this does not fix it, I think additional air handler insulation may be a good idea.