HI. I recently did a major overhaul on our house in Atlanta, due to a
fire last summer. My house is about 2500 sq.ft. and the sub contractor
put in a 4 ton unit with three zones. We are having a great deal of
difficulty getting the temperature to be below 78 degrees, especially
on hotter mid ninety afternoons here. the AC guy says the best you can
expect is a 20 degree difference on a hot day from the outside
temperatures. Is that right? We had a 3 ton unit previously that kept
us at a comfortable 70 (brrr) all year. Oddly enough, the zones
furthest from the unit keep a cooler temp more consistently. Any
Something's got to be wrong if your old 3-ton unit was adequate.
I'd have a blower door and load analysis done on the house to see how
the numbers come up. You might also get a thermometer and read the
temperatures going into and coming out of the AC at the closest
register (after it's been running constantly for maybe 1/2 hour) to see
if the differential is in the right ballpark. Did they tell you the
capacity of the air handler in cubic feet/minute? You can have someone
do calculations given the humidity, temperature differential and air
handler cfm's to see if you're roughly getting what you should out of
In Arizona it can be 120 degrees outside and plenty of houses and buildings
are 70 degrees or so inside!
Might want to have another company look at your system. Maybe they did not
install what you paid for? Something is fishy here.
If you can, post the brand and model of your 4 ton unit (read label on unit)
here along with the square footage of your house. One or more of the experts
here should be able to tell you if this is in fact a 4 ton unit.
"beth" wrote in message
OK, Sorry for the delay in responding. I really appreciate all the
It is a Copeland Scroll version of a unit made by Goodman Manufacturing
company out of Houston, tx. the model number is #CLJ481-C. I hope
this helps. IN the meantime I am having the a/c guys come back out to
do the temp. comparisons. The unit is running almost constantly to
attempt to reach a cooler temp, and there is a significantly higher
temp near the ceilings. Thanks again!!
Searching on the internet I found that this is in fact a 4 ton unit...
Page 14 or search the text for CLJ481
So it would seem that the unit is not working properly if you in fact had a
3 ton unit which worked OK previously.
The 20 degree rule applies to the difference between the air at the
return and what's coming out of the registers. I'd _guess_ there is
either something wrong or you have a very poorly insulated/leaky house.
4 tons for the avg 2500 sq ft house should be good.
I'm no A/C expert but even I know that four tons for 2500 sq. ft. is
too little. I've come to believe that the rule of thumb (for standard
eight foot ceilings) is one ton for every 400 sq. ft. I think you're a
couple of tons short.
It was 102F outside the other day (not counting the fact there was also
high humidity, which apparently made it feel like 117, and the A/C
happily kept the house at 72F. I have a 2 tonne air conditioner, total
condition space is 2000 sq ft with 8ft ceilings well sealed.
PS. I also have a heat recovery ventilator and didn't need to switch it
to recirc or having to run any additional dehumidifier, the A/C removed
any extra humidity the HRV might have been bringing in.
replying to New Wave Dave, Imnukingfutz wrote:
It may be fine and not undersized at all...I have 2300 sq ft and am only running
a 3 ton system and it works perfectly. Many other factors come into play other
than sq footage when sizing a system.
I have an even better one. My ex moved into a trailer when she moved
out last summer, one without A/C. She had a new furnace & A/C
installed last Nov. This spring she finds out that the A/C apparently
doesn't work.(NO cooling at ALL!) After several calls to the
installer, she finally gets a response that turns out to be a
different outfit responding to the call as a favor to the original
co. since they are going belly up. After about 45 min. of trying to
get some freon into the system since it is showing all the symptoms
of being low, one of the guys decides to check something really
stupid. It seems that compressors come pre-charged, and there is
some sort of valve at the intake and output that needs to be opened
when the system is being charged during install. You guessed it -
they had not been opened yet. As soon as he started to open the
valves heat started coming off of the heat exchanger and she was in
business. Guess that's why the original outfit was going under!
Good point! You would assume that someone installing something would test
it after installation to be sure everything is working properly, etc.
However I have worked for many companies which have "that one new employee"
who never does anything right, will not be sure everything is working before
leaving, etc. So if you get a bad "luck of the draw", might get one of these
guys installing something for you.
Usually the repair guys are well trained - experienced and can resolve these
problems. The installation department has the new employees typically.
(Sometimes a boss will keep sending the same installer out in an attempt to
educate him so he will do things right in the future... "You will keep going
out there until you get it working" is the thinking.)
"tim" wrote in message
I had the exact same situation as Bill. A new installation of an A/C
unit, the air that was coming out of the registers was not very cold,
and it seemed that no matter how long we ran it, the house would not
cool down much.
As time went on (for a couple of weeks) it got worse and worse until
the A/C did no good at all. We called the contractor who found a leak
in the freon. He fixed the leak, and the problem was instantly solved.
Night and day difference, we had no problem (even on very hot days -
100+) cooling the house to below 70. Took less than an hour of the
One additional note - we had the same problem again a few months later;
a different leak in a different area. After they fixed the second
leak, we had no further problems.
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