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Travis Jordan
 
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Default AC Advice Needed!

unix-freak wrote:
"Travis Jordan" wrote in message
m...
unix-freak wrote:
Greetings,

An AC man came out checked my system a few days ago and I was told
that I needed a bigger compressor/furnace.

Basically, it was 85 or so outside and 80 inside and no hope of
getting any cooler inside. Compressor output air temp was 99 with
the coil's input at 91. The compressor has a deck over it (was like
that when I moved there). There is 3 feet above the deck. He
checked the charge and said it was good.

Inside supply air was 70 degrees. Surface mount attic fan had
stopped, so the attic was 150 or so. The fan's bad so I'll replace
it today.

Anyway all that to say, the AC guy told me that I needed to go with
a 5 ton unit for my 1800 square foot home. I have a 3 ton unit now.
It's a Trane and the house is 21 years old.


What did his Manual J heat gain / loss calculations show that you
need? He DID do a Manual J, right? If not, call another contractor.


Not sure.

What is the return air temperature measured at the registers?


76
What is the return air temperature measured at the air handler plenum
(return side)?


78
If there is more than 2 degrees difference between the above two
readings you either have a leak or inadequate insulation on the
return ducting.

What is the supply air temperature measured at the air handler plenum
(supply side)?


68
Subtract the last two - What is the delta-T (temperature drop across
the air handler)? Should be 17 - 22 degrees. If it is outside this
range then I'd call another contractor.


Somethings not right. There's not much condensation from the
condensor coil either. Maybe I need to get in there and clean it.


I assume you mean "There's not much condensation from the evaporator
(inside) coil..."

The most common causes of low delta-T a

1) undercharged refrigerant due to a leak
2) excessive air flow over evaporator (i.e.air handler fan set to wrong
speed)
3) dirty condenser coil

There are other less-common things that go wrong such as problems with
the thermal expansion valve (TXV), bad compressor valves, bad reversing
valve, and more. About the only thing you can do as a homeowner is
check the outside coil to make sure it is clean. If it is, you really
need to call a qualified serviceperson (I would submit that the one you
called last time who recommended a larger unit is not among the list of
service people to talk to).

Please post back when you have a final resolution.