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Old 07-14-2011, 03:31 PM   #1
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poor AC performance


I have a 2100 sf house in Florida with what I believe is a 4.5 ton 13 SEER unit. House faces East. House and AC are 5 years old. Since day one I have been betteling in the summer to get the house below 80 and the AC runs constantly. Installer says the unit is the correct size and is running properly but "It is hot outside", says I should only expect to get btw 15-20 degrees cooler than the outside air temp. I am trying to troubleshoot this from 7500 miles away as I am currently deployed in Afghanistan with the military. I also have a duffuser in the ceiling in the fron tbathroom that will build up condensation to the point of dripping, the diffuser is about 18 inches away form a skylight. Any ideas?

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Old 07-14-2011, 04:06 PM   #2
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For condensation to "drip" from bathroom register one of two things is happening. Either humidity in room is very high or register is very cold (both allowing register to hit dew point) I would sugest finding another company to give a free second opinion. The original installing company has not solved anything for you yet. Make sure filters are clean, ect.

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Old 07-14-2011, 04:08 PM   #3
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poor AC performance


We need the temperature at return and after evap coil. The temp diference between these 2 points. It will show the Delta T. AC should have a delta T 16-20

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Old 07-14-2011, 04:41 PM   #4
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I am guessing the room with the dripping diffuser is due to humidity but the question is why?? I even replaced the metal diffuser with a plastic one to try and stop it but no luck. I went into the crawl space and sealed all around the boot abov eth ediffuser and still nothing, could it be due to its proximity to the skylight? I will see if my wife can take temp readings and I will post them as well. I had one company look at it and said the ducting was too small and because of it, the air was moving too fast by the diffusers and not passing down through them, thney also said at the end of th erun of duct, the end plate was of the wrong design and the warmer air was now doubling back agianst the cooler air. Sounded about right to me but what do I know, I fight wars for a living not ac units.
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Old 07-14-2011, 05:36 PM   #5
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You may want to do a heat load calculation to make sure it is the right size for the house. Or get the Missus to do it. Not too complicated, just need an open mind and a tape measure.

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Last edited by yuri; 07-14-2011 at 06:17 PM.
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Old 07-14-2011, 06:06 PM   #6
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Also have her post the model number of the outdoor unit. No such thing as a 4.5 ton A/C unit.

Does the register get condensation on it while the A/C is running, or after it stops.
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Old 07-14-2011, 06:24 PM   #7
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I would like to thank you for serving our country. You are very appreciated by my family.
I am sorry that your house is not working properly for your family. With the answers you are getting from your current tech I would look for another opinion. Not sure there is much you can accomplish from where your at.
Good luck and be safe.
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Old 07-15-2011, 03:05 AM   #8
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@BEENTHERE..Not sure where I was getting the 4.5 ton number, as I said, I am no AC expert. Will have the wife check it out and post the model number, as far as the diffuser goes I can't tell if it is building up condensation with the AC not running because the dam thing hardly ever shuts off! I have someone coming out to do a load calc hopefully Monday, issu will be seeing if the installer will rectify the problem for free if it turns out the unit is too small. Not holding my breath there. IF it is undersized would one of those Mr Slim type units put in the living room, which is the hottest and biggest room in the house, do the trick?? Thanks for all the input
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Old 07-15-2011, 04:51 AM   #9
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If its a 5 ton and too small. A MR. Slim would help. You/they could install it and then remove/close off the supply/supplies from the central to that room, and have the extra supply now available added to other rooms.
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Old 07-15-2011, 05:35 AM   #10
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Can you trust them to do the load calc properly and not fudge the #s to save their butt if they screwed up? I would do it myself to be sure they are honest. Unless they give you a VERY detailed printout and you can read and interpret it and double check their #s I would want my own done.
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Old 07-15-2011, 10:24 AM   #11
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@Yuri, I have someone who is not affiliated with eithe rthe builder or the AC company coming out to do the load calculation. Come to find out it is a 3.5 ton, good thing I am better at fighting than I am at figuiring out ac sizes. Here are the numbers from the indoor and outdoor unit. Indoor unit: FY4ANF042 outdoor unit:25HBA342A300. Thanks for the help. Just sent an e-mail to the builder, not sure how far that will get me, since they pretty much su*k. I am open to any and all suggestions.
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Old 07-15-2011, 02:05 PM   #12
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I would put a 3 ton unit in that size of house where I am and we have 50% the cooling load you do because of the humidity and peak temps. Sounds like it may be small too me, but it depends on house construction and insulation etc. Sounds small to me.
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Old 07-15-2011, 04:08 PM   #13
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3 to 3.5 tons is fine for a 2100 sq ft newer house here also. Depends how far south in Florida, a 3.5 ton is plenty also.
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Old 07-16-2011, 08:25 AM   #14
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@beenthere, I am in Jacksonville FL where in the summer temps commonly hit triple digits
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Old 07-16-2011, 08:37 AM   #15
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Good chance, it was only sized to do 20F difference between outdoor and indoor.

Also as good a chance if not better, that the duct work is under sized.

A temp delta across the coil should be taken. If the charge is good, and no problems in the refrigeration system, and the delta is less then 20. A 4 ton could be installed in its place. Which would give you a few(5 or so) cooler temp in the house.

PS: a temp check at the registers to see if its gaining too much heat should also be taken, before just increasing size.

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