I made a post a few weeks ago that I had 4 closets with surface mold. My wife insisted we have the ceilings cut out and replaced which I did to appease her. But the underlying issue is still there.

First it started with 75-80% humidity in the closets and moldy smell. I found what I thought was the source being a clogged AC condensate line in the wall sweating and putting a ton of moisture in the walls, where the wall cap and insulation the line was running into was wet to the touch.

I cut that line and re-ran it to the emergency drain line straight out of the house for now. Had AC company check it out and they say the unit is working fine. Bathroom started smelling better afterwards.

Now a couple of weeks later I have 75-80% humidity in the entire house throughout the day even at night with the A/C cranked to 69 degrees.

I have been in the attic to check for leaks 1548472 times this past week and nothing. No known roof leaks, no plumbing leaks from what I can tell as there is no water damage throughout the house.

I am dumbfounded on what to do next....

How and where are you measuring the humidty. I'd think if it's that's high and you're running it that cold you'd have condensation forming in places. Did AC co check your evaporator coils? Did they mention the humidty at all?

We put a whole home dehumidifier in our house. The variable AC handles much of the load, but there are a few weeks in the year where the variable AC handles the humidity. I keep our humidity level set at 40%.

I have 3 separate gauges and my thermostat gauge around the house. All between 68-80%

And when they came out it was two weeks or so ago when there was only humidity in the closets.

They said everything on AC running fine

My thermostat always gave wrong readings. I think it's because the sensor was on the back where the hole in the wall is for the wires. I'd probably call them back and tell them it's been two weeks and the humidity is too high and have them come back out. Have you turned off all water and checked your meter to see if it changes to see if you do actually a leak somewhere?

When the AC is running to 69 degrees, how long does it run to get to that set point? This sounds like your AC system either isn't operating efficiently or it's massively oversized. Has anything changed with the AC system or your house since you noticed this issue? Houston should be close to 100% humidity right about now and that's going to find its way inside if the AC can't ramp down and dehumidify a bit.

Going from 72-74 down to 69 I would say it takes about 45 minutes to an hour on a wild guess to get there

69 is at night.

During the day it would have trouble reaching 69 for sure. Normally keep it around 75 during the day

When it's set to 75, how much is it "on"? Does it run all day long continuously, or does it come on for 15 minutes and shut off for 30 and then on for 15?

BrazosDog02 said:

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213 Grove said:

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Going from 72-74 down to 69 I would say it takes about 45 minutes to an hour on a wild guess to get there

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Man, it sure sounds like the system is grossly oversized. Personally, I don't think it should be able to reach that set point at all in Houston in July.

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Really? It's currently 74F outside and its been getting into the 70s at night. If your HVAC can't get to 69F, I think you have either an insulation or HVAC problem.

4 closets? Are they in the same part of the house or scattered? Was the surface mold on all the walls or just one particular wall or exterior wall? Do you have good air flow out of all of your vents? What is the condition of the condensate pan? Evidence of water? Has it always been bad or just a recent development? Any work done recently? Lots of questions just trying to get a feel of the situation.

My first expedition into the attic would be to check for duct leaks
#1 EZ to seal would be return air plenum and would throw insulation over it for good measure
#2 not fun checking all the supply ducts UGH a laser temperature gun might help when cold air running through
#3 if system is over/near 20yo, then it's time to replace system & seal all ducts in the deal

Since NOT a HVAC guy, take this with a grain of salt
Just bad experiences a talking

I do not know his design specs, temperature, humidity, AC size, or build quality of the home. Builders often spec oversized units because they don't want to listen to people ***** and moan about not being able to keep their AC at 75 when it's 110 outside. I just can't figure what else would cause his high humidity aside from having his fan set to on instead of auto. Just trying to work through it. Even at 74 outside, if it's properly sized, 69 degrees should definitely yield less than 60% humidity unless it's a builder grade single speed unit.

And at that point, I'd run that thing down to 60 and see what happens. What's the temp split on the unit?

Another issue I have had with bonehead HVAC companies is not properly configuring the air handler. Most of them can accommodate multiple tonnages so if they have an air handler defaulted at 5 tons and your outdoor unit is 3, then it's going to be humid and inefficient. Some air handlers have dehumidification options with the right thermostats and those will ramp down the air speed to increase dehumidification but again it has to be set up by the installer. I haven't a clue if any of this applies. Just thinking out loud from 20 years of misery trying to fix my own issues that are wierd like this.

Fan is on auto and not set to on ?

I have seen high humidity levels when the coil is not draining condensate properly

What ton size is the unit and what is the heated square ft of the house ?

BrazosDog02 said:

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I just can't figure what else would cause his high humidity aside from having his fan set to on instead of auto. Just trying to work through it.

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An attic duct leak creating negative air pressure when the system runs drawing in humid outdoor air is a possibility.

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Another issue I have had with bonehead HVAC companies is not properly configuring the air handler. Most of them can accommodate multiple tonnages so if they have an air handler defaulted at 5 tons and your outdoor unit is 3, then it's going to be humid and inefficient. Some air handlers have dehumidification options with the right thermostats and those will ramp down the air speed to increase dehumidification but again it has to be set up by the installer.

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Funny you mention this. I just went through a replacement of my 3 ton outdoor unit. The installer tinkered with the dip switch settings on the variable speed furnace. They turned off the Trane Comfort-R settings and set the furnace to think it was matched to a 1.5 ton unit.

Sweet Kitten Feet said:

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My thermostat always gave wrong readings. I think it's because the sensor was on the back where the hole in the wall is for the wires. I'd probably call them back and tell them it's been two weeks and the humidity is too high and have them come back out. Have you turned off all water and checked your meter to see if it changes to see if you do actually a leak somewhere?

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Ecobee? Same here, that sensor is ***** I have 2 old Honeywells near it to get an accurate humidity reading.

Yep. I have 3 other sensors spaced throughout the house to get humidity reading and actually trigger the bathroom fans to come on

Do you have an Aprilaire ventilation system to pull in fresh air when it's "cool" outside? I found out my intake was stuck open even when it was above any reasonable set point and once I fixed that the humidify went way down in my house. Not sure what was going on but I just turned off the ventilation on the thermostat and then tightened the set screw to prevent it from opening again by accident. I'll look at it again in the winter.

Use a little plumber's putty to fill the hole on the back where the wires run through.

I don't really have any specific solution, but a few notes and things to think about:

1) A properly sized system should be running 6-8hrs plus in a 24hr period in 95F weather. If you are running less than that, it is oversized.
2) Make sure your fan is not running continuously. That evaporates water from the pan under the evaporator and humidifies your house.
3) These oddball low heat load days like we have had recently, coupled with rain and high humidity outside, can cause high indoor humidity. We normally get some days like that in the fall and spring, not in July. The ac just isn't running enough to dehumidify.
4) You need to get immediate control of this situation until you can determine a root cause. I would suggest getting the $300 Hisense dehumidifier from Lowe's. I have one and use it on these oddball days. It is a workhorse.

Oh, and something else that deserves its own post - don't say a word about this to anyone.