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Old 08-09-2008, 03:29 PM   #1
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Still having problems with insufficient cooling in my house. I had an a/c tech come out and take temps from the room air entering the coil (where the squirrel cage is at) and that air was 80 degrees, he then measured the air exiting the coil and that temp was 51 degrees...can anyone tell me is this coil performing like it should...? (outside temp was 97 degrees and the attic temp was 118 degrees.)

After he took these temps he said the coil was fine that my duct work was funky...he said the transitions in my ducts need "triangle shaped duct board" for better air flow...can anyone give me an opinion on this...I've read that duct board really isn't a good substitute for this....

(He used a digital thermo and punched a hole in the top of the air handler and inserted a lengthy wire to get his readings).

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Old 08-10-2008, 05:59 AM   #2
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What was the space temp at the time? If it wasnt 80 degrees, your pulling attic air through the return. Cant really find fault with a 30 deg drop accross the coil, if anything its a little low.

At the return air openings, diffusers, will they hold a tissue if you lay one accross it? What is the total sqin of all the return openings?

Is there anywhere your drawing outdoor air into you system, a scuttle kit or combustion air for something?

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Old 08-10-2008, 07:21 AM   #3
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that 80F return tells me that the house inside is .....80F if the interior around the stat is lower then 80F you might be sucking some of the 118F atic air into the air handler killing your discharge and with that killing your design tonnage.
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Old 08-10-2008, 10:52 PM   #4
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The space temp if your talking about the room temp was the same...80 degrees. And what exactly do you mean when you say that the 30 deg drop across the coil is a little low...?

Yes, the return air will hold a tissue and the return is 21"x 26". (only have one centrally located in a 1636 sq. ft. house).

And no, no scuttle kit or combustion air drawing outdoor air into the house. Thanks for your response 8 Ball.

Actually biggles...the interior air around the stat is the same as the stat...thanks for your reponse biggles.
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Old 08-11-2008, 04:59 PM   #5
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Your return air duct/opening is too small. Is it loud when the AC is on?

How many supply registers, and thier size?

Do you have a 21/2 ton AC?

By low, I mean that normaly you see a 15-20 degree drop. If you have 30 degrees, your undercharged or dont have enough airflow. Im thinking airflow.

Last edited by 8 Ball; 08-11-2008 at 05:03 PM.
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Old 08-11-2008, 11:01 PM   #6
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Hey 8 Ball to answer your questions...

No...my return air duct is not too loud.

I have 9 supply registers that are 9"x5 1/2" in a 1636 sq. ft. house.

My unit is 4 tons.

Thanks for responding 8 Ball...
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Old 08-13-2008, 05:03 AM   #7
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Four tons? That would be great if you were in a 2400 sqft home. Are both the airhandler/furnace and outdoor unit 4 tons? How did you end up with an oversized AC.

Even if your ductwork was sized for the additional airflow required for the larger AC, it will never work properly, let alone the fact that it will short cycle and never be able to dehumidify properly, increasing the probability of premature failure. Bigger is not better. Once you go beyond the accepted design criteria, the only certainty is poor performance.

Your return air size indictes you ductwork is not sized for a 4 ton unit, I would expect to see twice the size you have indicated.

Last edited by 8 Ball; 08-13-2008 at 05:20 AM.
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Old 08-13-2008, 03:43 PM   #8
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8 ball is 100% correct . your ducts are 2 small for the system and a 30 degree drop is wayyyyyy to much. how is the air flow on the supply vent . I suspect the system is freezing up for the precisely the reasons stated above. the fact that its not reaching temp can be corrected but it wont dehumidifiy properly dont give up yet.
only cheap installers even look at fiberboard . find a company that works with metel and at least knows somthing about ac a guy walking away from that saying your good doesnt

Last edited by geo fan; 08-13-2008 at 03:49 PM.
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Old 08-14-2008, 10:02 AM   #9
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Hey 8 ball...that's just it...during the heat of the day my unit will not cycle...it will not take the temp in the house below 81 degrees...

During hot Houston weather typically between 95 to 101...with the subtropical climate that's here ( extreme humidity)...my a/c will not cycle off and can only bring the temp to 81 degrees.

Now at night or in the morning when it's not so hot...the unit can bring the temp below 81 degrees...but never during the heat of the day.

This house already had the 4 ton unit when I moved in...and I think the unit was oversized due to the climate of Houston and also because this is a patio home...skylight in the kitchen...large sliding patio glass door in the living room...also in the master bedroom...all the windows including sliding glass patio doors are single pane. That's just an assumption.

This is a 4 ton trane inside and out.

So 8 ball should I expand the return air from 21" x 26" to 42" x 52" (this is a wall cavity return air) or should I put in an additional return duct...? And if so, what size duct should I use, what size should the return air vent be and what strategic location should this new return vent be located...? The present return air vent is located in the hallway near the entrance of the living room. Thanks for your help 8 ball.

Geo, so you say my ducts are too small? What size should my ducts be? Thanks for your help Geo.

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