72 degrees to be comfortable

dantisMay 30, 2012

Hi all.

I had new system installed last summer, now turned on for the season. After reading here so much that people hav there settings at 74-76�' why is it I need 70� to feel "cool".? RH is always around 59%. Is that too high? If so how do I dry things out? My air handler is variable speed and set to operate as 50% speed for first minute, 100% as needed, than operate without condeser for 3min or so....what should my hideal humidity be? What is a typical cycle time?

Thank u

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A relative humidity of 59% is high. Ideally you should be in the 45-50% range. Your variable speed air handler should be operating at a low speed for long periods of time to dry out the air.

Can you post more information about your system (sizes, model numbers, thermostat, etc)? State your location and the size of your house. In addition do your windows and doors have a tight seal?

    Bookmark   May 31, 2012 at 7:27AM
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Post complete model numbers of outside condenser and inside air handler.

What is a typical run time cycle, at what indoor thermostat setting, and at what outside temperature.

What mdl thermostat do you have?

Your problem could be as simple as slowing the CFM setting at the air handler. Any idea what the setting is now? That would be my starting point.

I will assume you are sized correctly.


    Bookmark   May 31, 2012 at 7:44AM
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I will post as much info as I can find tonite. I hope its that simple....its brand new....

    Bookmark   May 31, 2012 at 11:20AM
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The 3-minute run time after compressor shutdown will put a lot of that humidity back into the air. 1 minute should be better.

    Bookmark   May 31, 2012 at 4:02PM
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Good point by weedmeister. Fan should be in auto setting not the on setting and should run no more than one minute after condenser shuts down. With three minutes, you are just reintroducing humidity into your house after paying to have it removed. This change will require an adjustment from your installer.

This could be a big part of your problem.


    Bookmark   May 31, 2012 at 4:53PM
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OK, sorry to take so long to get the specs. Havent exactly needed AC recently in Mass, thanks to the April weather in June.
Air Handler - American Standard Model AAM7A0C48H41SAA
Compressor - American Standard Allegiance 15, 15 SEER, 4 Ton Model 4A7A5049E1000AA

I have 2 thermostats, White Rogers (sorry forget model #), but 1 is upsatairs, the other downstairs. There are dampers on the duct work from the air handler depending on which zone is calling for cool.
CFM/Ton is set for 350, selectable 330, 350,370 or 390
Cool Off Delay is set for "Enhanced"- Compressor ON, 50%CFM for 1 minute, the 80% CFM for 7.5 minutes, then 100% "if necessary" then Compressor off 50% CFM for 3 minutes.
This setting is dip switch selectable for 1.5 minutes @100%, "No delay", 3 minutes at 50% and enhanced. I have thermstat fan set for "AUTO"
Last DIP switch is "Airflow Mode" selcatble for Torque or Constant CFM, currently set as "torque"

House square footage: approx 3700 sq ft.

Anothe note when I inspected the coils on the air handler, there is very little "white powder" residue on the door, is that normal from the install or do I have a refrigerant leak? It was very little.

I also found I did not have a filter installed, so I installed a MERV 11 filter, which may slow down air flow a bit.

As mentioned in the initail post, the house get cool, but humidity will creep up to 55-60% even though temp remains at 72�.

After digesting info, any helps or hints to getting the humidity out will be greatly appreciated. System installed July 2011.

Thank you

    Bookmark   June 8, 2012 at 9:08AM
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How long does your AC run before it satisfies the call of the thermostat? We have been having an usually cool and wet start of summer in the Northeast. Perhaps the cool damp weather is not allowing the AC run sufficiently long enough to dry out the air. How did the system perform in August 2011?

Are you keeping the windows closed? Opening up the windows allows the humid air to enter.

Has the HVAC contractor reviewed your set up? Any ideas?

    Bookmark   June 8, 2012 at 10:57AM
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Itll run about 10 min or so....Cool and wet now, but it wasnt in April :) August 2011 was pretty much the same, would cool but not get down to 45-50% RH. Windows are closed..

    Bookmark   June 8, 2012 at 11:32AM
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Do you have a lot of outside air infiltration into the home? Are your ducts outside of the structure envelope? Did you get new ducts with the new system? If not, were the old ones sealed well? If new ducts, are they sealed well?

    Bookmark   June 8, 2012 at 9:04PM
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Could this be a zoning problem? If only one zone is calling for calling how is the excess air flow handled? Perhaps the zoning is causing the system to short cycle.

Does the 3700 square feet represent the first and second floors? What is the area of each floor?

Why did your furnace have no filter? Did the contractor forget to install one?

Have you set up an appointment with the HVAC contractor to review the problems? You want to get this done before the one year anniversary.

    Bookmark   June 9, 2012 at 11:50AM
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