How do you tell condenser size without tag? - http://www.hvacmechanic.com/ Forums
Original message
| mitchedo
 |  "How do you tell condenser size without tag?"
, posted Wed 23 Jul 23:36  
How in the world did a service tech determine the size of my sister's dead central AC unit when there wasn't a legible number on the tag on the condenser unit? He even wrote on the work order that the numbers are illegible. Can you tell by the size of the condenser? Did he read the numbers off the compressor and use that? I think he grossly oversized the replacement unit and won't return any phone calls. We have to work with him because the insurance company sent him. He did not measure the house or do any sort of calculation to size the AC.
Now, for the rest of the story for those so inclined. My poor sister is a single mom with two girls -- trying to get by on $14 an hour and no welfare.
We live in a suburb of Salt Lake City, so we don't have a tremendous heat load for our AC units here.
My sister just bought a little house, about 1200 sq feet on the main, and 1200 in the basement. The basement is below ground level except for about a foot or two all the way around.
The house came with a warranty and the central AC just died. It was an ancient Lennox that was so old, all the writing on the tag on the condenser housing was unreadable. There were some readable numbers on the compressor.
The short story is, the AC quit cooling so she called the home warranty folks who sent out a tech. He spent about 15 minutes at the house, said the unit was a total loss, and she'd get a new one.
Well, he sized this thing at 4 tons. My sister, my parents, another sister, and myself all live within a few miles of each other. The largest AC unit on any of our houses is one with 1400 sq feet on the main, and 800 in the basement, with about 1/3 of the basement height below ground. This house has a 3-ton system.
My parents' house is of the same construction as the house in question, with the same insulation in the attic, and is slightly larger than my sister's house. It has a huge tree on the west that shades the house pretty good. This house has a 2.5 ton unit that works swell. My house is a bit larger, not as well insulated, and has a 2.5 ton unit. I have a huge tree on the south. My sister's house has no shade falling on it.
The insurance company says they have to put in the size the tech says. I say this tech has grossly oversized the unit. It seems the AC should be sized at 2.5 - 3 tons, and they're going to install a 3.5 ton evaporator, and a 4 ton condenser.
Does this all sound a bit off? What is sis in for if they install this system?
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Semper fi
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Replies:
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| Freon
| "Re(1):How do you tell condenser size without " , posted Thu 24 Jul 16:13
Simple answer. Analyze your existing duct system thoroughly and use that data to support your size determination. You duct system will tell you how much air flow you can support. The air flow will tell you what size unit you can have. Example... Lets assume each room in the house with a supply register has a 6" duct then count all the supply registers, multiply by 110 and divide by 400 to get the approximate tonnage that your duct system will support.
Too big a system will cause bad wind noise at the supply and return registers (high velocity due to too high static pressure from oversized blower) and could cause the indoor coil to freeze (not enough air flow so not enough heat transfer). Freezing is not as likely due to your desert climate (no humidity).
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| hollywood
| "Re(1):How do you tell condenser size without " , posted Thu 24 Jul 14:37
4 tons of cooling sounds like a bit much for her situation.Having an oversized unit will cause short cycling of said unit.This will in turn cause the elec. bill to climb to a noticable difference.As far as smaller coil size-many manufacurers make a single coil to accomodate multiple sized condensers.You can also find out the indoor(evaporator)coil tonage,if it is a lennox coil-by the model # of the coil.
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| mississippi
| "Re(1):How do you tell condenser size without " , posted Thu 24 Jul 12:41
the compressor model and serial #'s can be used to find size.is the basement heated and cooled if so unit is not oversized.load calc a good idea but not alot can be done as far as sizing because original duct work sized to original unit.
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| | mitchedo
| "Re(2):How do you tell condenser size without" , posted Thu 24 Jul 13:34
I forgot...
Might the compressor be a model used in a variety of sizes of condenser units? I wondered if maybe it was good for up to a 4-ton and that's what the tech used to size the unit?
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Semper fi
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| | mitchedo
| "Re(2):How do you tell condenser size without" , posted Thu 24 Jul 13:31
Thanks so much. The basement is climate-controlled living space. However, it has very little to no heat load. It might be as hot as 76 degrees down there on a 100 degree day outside. The only thing that makes the basement uncomfortable right now is the high humidity outside right now. It's about 40%, which really makes us desert dwellers whine. Before the existing unit died, she kept all the basement registers closed.
As a comparison, I have a 1400 sq ft basement that is ground level on the west, below ground level on the east. My basement heat load is much higher than hers, and I cool my whole basement with two 5000 btu window units.
Is there any concern with a 3.5 ton evaporator and a 4 ton condenser unit? I think the whole system is grossly oversized; does that affect the smaller indoor coil?
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Semper fi
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| | yuri
| "Re(3):How do you tell condenser size without" , posted Thu 24 Jul 19:22:
The size can be gotten from the model # off the top of the compressor. Most Lennox units use Tecumseh or Copeland compressors and if you get it for me I may be able to decipher it for you. Or phone a refrigeration parts supplier and ask for a replacement compressor and they can cross reference/size it for you. Try using a magnifying glass to read the numbers on the condenser label. Try rub some graphite powder on them to "lift" them or rub some cooking oil on them and use the magnifying glass.
Yuri
[this message was edited by yuri on Thu 24 Jul 20:59] |
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