Condensation leaking from cooling coils and plenum

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Old 11-06-16, 09:00 AM
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Condensation leaking from cooling coils and plenum

Two year old home in Austin, TX. Water collecting in auxiliary pan. Temperatures were seasonal(75-90 degrees), with unusual higher humidity due to rain storms. The house is kept between 72-78 degrees. The source of the 1/2 inch of water in the pan is coming from the mastic joint between the cooling coils and the plenum.
A technician offered repairs such as creating an angled flashing piece so if water is being sprayed out into the plenum, it will be diverted back to the internal pan. He also offered replacing the cooling coils! We've yet to have the original installer evaluate, but his first impression was to reduce the fan speed. By the way the unit cools the home nicely.
Questions: 1. Will reducing the fan speed correct the problem without affecting humidity control in the home or the efficiency of the unit?
2. I was amazed at all the vents... I understand the post P trap vent on the primary drain, but the pre-trap vent? Also, should there be a trap on the auxiliary drain? I understand from researching that the 'positive' blower side will not allow condensation to remain in the pan.....What is thoughts regarding the drain design?
3. Any other thoughts?
Thanks!

Link to pictures: https://goo.gl/photos/wNovGeGNGz6xJ3v1A
 
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Old 11-06-16, 09:34 AM
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In that application, I would blow out the drain, lose the trap, measure the temperature drop across the evaporator coil, measure the external static pressure, verify that the furnace airflow setting matches the condenser size, verify that the coil and filter are clean, ( we don't want a manual up against the inside of the evaporator coil).

It is unlikely that a splash guard is required with that application.
 
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Old 11-06-16, 09:50 AM
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It does sound like more diagnostics are required. Drain line was clear and the filter was changed. Thanks for your thoughts.
 
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Old 11-06-16, 02:17 PM
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As Houston mentioned, make sure the coil is clean so the condensation is running down the coils and not blowing off.
 
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Old 11-06-16, 03:13 PM
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The one technician cut out a small opening in the plenum and the coils looked good. Thanks.
 
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Old 11-06-16, 03:23 PM
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The plenum only reveals the outlet side of the evaporator coil. The inlet side of the coil can look very different.

I have seen a 5 ton furnace installed with a 3 ton condenser cause water to blow off of the coil.

I have seen a dirty coil cause water to blow off of the coil.

I have seen lack of refrigerant cause water to blow off of the evaporator coil.

When you shine a flashlight down the primary drain line tee, does the drain appear to be flowing correctly? A poorly sloped drain line can cause water problems.

Do you see water in the secondary drain line tee?

A manometer reading inches before the furnace, two inches before the coil and a few inches after the coil would be of assistance.

You want the first two readings below .6" water column ( drop the positive and negative in the equation). Removing the coil panel would reveal a safe spot to drill a 1/4" hole before the coil.
 
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Old 11-06-16, 05:13 PM
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Houston I appreciate your thoughts. It is my son's home, and I won't be in town until December.
Your comment about the fluid flow piques my interest. The pics were from Saturday. The AC was running and there was now water in the auxiliary pan.
If the 2 vents were capped, I.e. the one prior to the trap on the main drain and the vent on the secondary drain, would the air force the condensation out of the AHU?
 
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Old 11-06-16, 09:58 PM
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The tee before the trap is a clean out and the tee after the trap is a vent. The vent should not be capped unless you are blowing out the drain.
 
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