new HVAC not cooling

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We recently had a contractor install a new unit (a Bryant Puron 2.5 ton in a 1500sq/ft 3br/2ba home) a couple of months ago. This week we've had some really warm weather with temperatures in the 90s nearing 100 degrees. The problem is the unit is not cooling the house. The unit runs all day and doesn't drop the temperature below 78 degrees. Our older unit never had this problem.
We called the contractor that installed the unit out and he said that was normal. He told us that these units won't cool more than 20 degrees below the ambient air temperature. He also said that the fact that our ducts are in the celing makes this problem worse. Something doesn't sound right here. I mean, our old unit cooled the house fine and that unit was smaller (2 ton).
What's going on here? Is he correct, ignorant or simply lying? Can you guys educate me on this? Should this unit be capable of cooling the house better than it's doing now?
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On Jun 9, 5:11 pm, snipped-for-privacy@gmail.com wrote:

Not expert here, but it sounds like the guy is trying to swat you away, at least for awhile. Exactly how 'cool' does the new unit actually get the house now, vs what your old one got it to?
I would wait for some good feedback here and get your ducks in a row before you pressure the AC guy too much more. That way you'll maybe be able see through some of the smoke screen excuses he might be giving you.
Good luck. Post how it all gets resolved.
Brian
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snipped-for-privacy@gmail.com wrote:

I'm in Texas. It's hot here. My house is bigger than yours, and 3 tons will cool it as low as I want to go.
The "20 degree" rule of thumb is across the A/C. So if your house is at 100 degrees, the A/C should be able to blow (more or less -- it's just a rule of thumb, not Gospel) 80 degrees. Then, once the house is cooled down to 80 degrees, it should be able to blow 60 degrees. Etc.
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wrote:

Btu is Btu. If the new unit is larger, it should cool to a lower temperature than the old one. Proper sizing aside, the higher capacity can remove more heat. Proper sizing gets into things like humidity control where to big is no good. If the 2 ton unit was good, the 2.5 ton should be at least as good at reducing the temperature.
I'd do a quick check of the basics first. Are the duct leaking? Was something left undone or is airflow blocked? Check the temperature of the air entering and leaving the AC. It should have about a 20 degree drop across the coil. Cooler at night with no sun load? By cooler, I mean the differential between outside and inside temperature. Personally, I think there is a problem and since it is new, get him back to check things, such as the pressures in the unit. There may have been a leak.
There is a lower limit, of course. At 100 degrees, a properly sized unit won't get it much more than 20 to 25 degrees cooler than outside, but if the old one did, the new one should.
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On Mon 09 Jun 2008 06:52:50p, Edwin Pawlowski told us...

The design and sizing of a system is also somewhat dependent on where you live. We live in the Phoenix area. Few people here would be happy with 95 degrees inside on a 120 degree day, a 25 degree differential. We can easily cool our house down to 70 degrees on a 120 degree day, although we usually keep it at 75 degrees.
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Wayne,
Your reply makes me curious........how many tons of a/c do you need to be able to get a 50 degree temperature drop for how many square feet of living space? What would be a typical electric bill during the summer months? Thanks,
Smarty
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It's a 3 ton high efficiency unit. House is 1500 sq. ft. The walls have a 6" insulation space with R50 insulation, as does the roof. The house is 1- 1/2 years old. We're on "averaged billing" which runs $165/mo. year round. It's also an all-electric home.
Wayne...
On Tue 10 Jun 2008 06:56:12a, Smarty told us...

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Check the basics first. See if the pipe leaving the compressor is cold and sweating, if it is, its probably charged right. Also check to see if some ducts were closed inadverdantly. Was there a new air handler put in too? Its possible the fan speed has changed. Also check if your filters are clean.
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The pipe leaving the compressor should be about 200 degrees F. When the system is running. Or even hotter. Fortunately, it's encased, and you can't touch it unless you remove access panels.
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On Jun 11, 9:49am, "Stormin Mormon"

Sorry, I meant the pipe going into the compressor should be cold The pipe could also be checked at the air handler.
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Yes, generally a suction line on a working AC gets cold.
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Not always. This may be the case with r22, but with 410a, the line barely feels warm at all.
s

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How does the system release heat, if the discharge refrigerant is "barely feels warm"?
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Beats me. I didn't design the shit. I have 3 systems with 410a and all of them just barely feel warm right out of the outdoor unit, and they all work great.
s

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That is a lot smaller than I would have guessed. I too am in a 1500 square foot house, but in the northeast, have 3 tons of a/c, and probably average about the same electricty cost as you do, but I have a 60 year old house with much less insulation and never need to pull the temperature down more than about 25 degrees, usually only 15 degrees. I also have a hefty winter gas bill for heating. I would have imagined that Phoenix was a lot more tonnage of a/c but apparently not.
Smarty
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The major difference is that my house is new and heavily insulated. Similar size houses here that are older and less insulated might need up to a 5 ton unit.
On Wed 11 Jun 2008 04:38:31a, Smarty told us...

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I'd be curious as to what material you were ripped off for that claimed R-50 in five and a half inches of wall....
do tell....
s
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On Wed 11 Jun 2008 05:55:04a, S. Barker told us...

I have no idea what it is. Only a certification of the builder that the insulation was rated at R50.

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You better look into the "certification" because I think you are entitled to a refund and have an easy claim. I know of no foam that is more than R 7.2" new, before stabilising at near R 6.7". I would like to know of any product that is better than R 7.2" foam, at even 6" thick that is only R 43.2 , 5.5" of R 6.7 foam = R 36.85.
There are also different foams which range from R 4 and up. Maybe he put in something like "reflextic" but I dont believe their "independant" rating and question product life.
In reality I dont see how a wall 6" total, with 5.5" of the best product on the market could be advertised at maybe more than R 43. I would like to buy a R 50 wall, so would anybody.
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On Thu 12 Jun 2008 06:22:36a, ransley told us...

As I said, I have no idea, and I don't even know if it's foam or another material. In any event, it's the best insulated house we've ever owned.
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