Trane CFM settings

I have a 4 ton trane XLI1400 and it has been adequate the past several years here in central Florida. Since, I have added 300 square feet of A/C space. What I really need is a 4.5 ton, but since they don't make it and putting in a 5 ton requires complete rework of the ducting, we have decided to stick with the 4 ton until it breaks - it is 7 years old. Certain times when it is very hot outside, the A/C can only get the temp down to 79 and no more. Coming out of the registers is 65, which is pretty good considering the outside temp is 93 or so.
My question: I can change the CFM of the fan from 400 to either 350 or 450 by changing some dip switches. Would either improve my cooling? Or does it really matter?
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On 8/27/2011 7:44 PM, Lawrence Borne wrote:

You might be better off upgrading your insulation, weatherstripping and windows. If the blower speed was properly setup during the original installation, you could hurt performance by fooling around with it.
TDD
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On Sat, 27 Aug 2011 20:14:36 -0500, The Daring Dufas

    You might be better off getting the unit fixed, because it is not working properly.
    14 delta ( 79 - 65 ) is a SURE sign of a problem.
    BTW, the outside temp does not change that. If it were 90 inside, and discharge 65 - 70, THAT would be a properly working unit ( and too small ). Your unit may or may not be too small, but it is SURELY not working right.
    You need to see 20 - 25 delta when it's running.
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On 8/27/2011 11:38 PM, .p.jm.@see_my_sig_for_address.com wrote:

Well hell, I thought his question was about whether or not his unit was big enough to cool the extra space. I assume he's going to get the unit checked out, cleaned and serviced. I've gone to a customer location to check a unit and found the speed jumpers plugged into max speed and the darn thing was blowing the condensate out of the drain pan. Um, my AC is leaking water, I think it has a bad thermostat. ^_^
I repaired an AC in a rental house in the Bohemian section of town and the tenant later called me and said the unit had a problem because it wasn't cooling the house good enough. I asked what the problem was and the guy said it only cooled the place down to 78F so I asked him what the outdoor temperature was, 105F was his answer. It was an old house with no insulation in the walls and old leaky to air doors and windows. I thought the AC was doing a darn good job. :-)
TDD
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On Sun, 28 Aug 2011 00:20:23 -0500, The Daring Dufas

How could he tell with a unit that is not putting out its rated capacity ?

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On 8/28/2011 12:52 AM, .p.jm.@see_my_sig_for_address.com wrote:

I suppose I subconsciously assumed that the unit was OK because he wrote that it had been adequate until he added 300 extra square feet of space and I get your point but cleaning and servicing is a no- brainer for me. We did a remodel for a customer and I convinced my builder friend to add several layers of filter to the return air because I'm always having to remove the evaporator from places that have been remodeled because they're so dirty with things like sheet rock dust, it's the only way to get the coil clean. I just had a question pop in my head as to whether the fellow added any duct work which would have possibly required some HVAC guys on site. The work he did or had done could have easily dirtied up his evaporator.
TDD
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    'Is cuter with lipstick on' ?
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On 8/28/2011 11:45 AM, .p.jm.@see_my_sig_for_address.com wrote:

That is what drugs and cheap tequila will get ya.

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300 square feet is not that much however you should have good tech check refrigerant and see that condenser and evaporator are clean.
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wrote:

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Sorry, I was not clear with my temps. Here is what I am getting currently:
The temps vary depending on time of day, for example:
This morning:
Outside temp = 82 F Registers temp = 64 F Condenser air = 94 F
Afternoon:
Outside temp = 92 F Register temp = 70 F Condenser air = 110 F
During the afternoon, the best I can cool the house is about 78 or 79.
From my talking to an A/C guy, he said a delta of 25 - 30 from register to condenser would not indicate low freon. ???
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