AC question(s)

	AC question(s)

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Subject

Author

Date

AC question(s)

wedge40

06-13-2006

Travis Jordan

wedge40

Travis Jordan

wedge40

trader4

Travis Jordan

wedge40

udarrell

trader4

cornytheclown

trader4

Stormin Mormon

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Posted by wedge40 on June 13, 2006, 10:03 am

OK, I'm going to start this thread and as I get more info I'll update.

I have 1100 sf house with (I believe) 2.5ton AC unit. When the outside
temp gets above 80 or so the AC unit will not shut off cause it can't
keep up, even thought the I have the thermostat set on 80.
I have only 6" of insulation in the attice and have two-by walls. I
had a professional come out to inspect the ac and he said my problem is
the units too big. If the unit was too big for the house wouldn't it
run for short periods of time and the shut down and I would end up with
a cold/damp house. Instead it runs constant.
Any clues as what really needs to be done.

V/R Greg

Posted by Travis Jordan on June 13, 2006, 10:39 am

wedge40 wrote:

> If the unit was too big for the house wouldn't

> it run for short periods of time and the shut down and I would end up

> with a cold/damp house. Instead it runs constant.

Sounds like the unit either isn't performing correctly or is undersized.

You can't use rules of thumb like "square feet per ton" to size air
conditioning, so I don't know how a tech would know that a unit was
oversized just by looking at it.

If you have an accurate probe-type thermometer you can do some
diagnostics by yourself. Start by measuring the temperature at a return
register, at a supply register, at the return plenum (attached to the
base / end of the air handler), and at the supply plenum (the output
side of the air handler). Also measure the ambient temperature in the
area of the condenser inlet (fins), and the outlet air temperature at
the condenser exhaust. Post those numbers and we'll see if that turns
up a useful hint.

Posted by wedge40 on June 13, 2006, 2:52 pm

I can quickly measure temps at every place but the supply side of the
plenum.
How accurate will this need to be be. I have a kitchen type instant
read thermometer that should be good to within a few degrees.. Im
guessing that we are looking for the temp differences between these
point so any inaccuracies will be constant from one measurement to
another.
I will also post the correct size of the unit.
Thanks Travis.

Greg

Travis Jordan wrote:

> wedge40 wrote:

> > If the unit was too big for the house wouldn't

> > it run for short periods of time and the shut down and I would end up

> > with a cold/damp house. Instead it runs constant.

> Sounds like the unit either isn't performing correctly or is undersized.

> You can't use rules of thumb like "square feet per ton" to size air

> conditioning, so I don't know how a tech would know that a unit was

> oversized just by looking at it.

> If you have an accurate probe-type thermometer you can do some

> diagnostics by yourself. Start by measuring the temperature at a return

> register, at a supply register, at the return plenum (attached to the

> base / end of the air handler), and at the supply plenum (the output

> side of the air handler). Also measure the ambient temperature in the

> area of the condenser inlet (fins), and the outlet air temperature at

> the condenser exhaust. Post those numbers and we'll see if that turns

> up a useful hint.

Posted by Travis Jordan on June 13, 2006, 5:06 pm

wedge40 wrote:

> I can quickly measure temps at every place but the supply side of the

> plenum.

> How accurate will this need to be be. I have a kitchen type instant

> read thermometer that should be good to within a few degrees.. Im

> guessing that we are looking for the temp differences between these

> point so any inaccuracies will be constant from one measurement to

> another.

Your kitchen thermometer should be OK for this application.

Is your supply plenum made out of duct board? If so you can poke a
small hole in it and insert the temperature probe. When you are done
simply cover the hole with a piece of *yes* duct tape.

Posted by wedge40 on June 14, 2006, 5:45 am

Travis Jordan wrote:

> wedge40 wrote:

> > I can quickly measure temps at every place but the supply side of the

> > plenum.

> > How accurate will this need to be be. I have a kitchen type instant

> > read thermometer that should be good to within a few degrees.. Im

> > guessing that we are looking for the temp differences between these

> > point so any inaccuracies will be constant from one measurement to

> > another.

> Your kitchen thermometer should be OK for this application.

> Is your supply plenum made out of duct board? If so you can poke a

> small hole in it and insert the temperature probe. When you are done

> simply cover the hole with a piece of *yes* duct tape.

First let me state one thing.. I didn't build this home or have it
built.. It was bought this way. I knew the problems going in.. This
statement will make sense as you read further.

Ok I'll try and answer a few question this morning and then this
weekend I can get the rest of the info.
I live in Southern Indiana with Bloomington about 10 miles away.
I didn't get any measurements last night when I got home since it only
hit about 77 yesterday. But that shouldn't be a problem this weekend
since it's predicted to hit the 90's by Friday.

I have duct board for all the plenums, and flex duct for the runs.
There is complete access in the attic and this is where my return lines
are. My supply lines are in the crawl space.. And when I say crawl I
MEAN CRAWL. I believe at most a two block space to work in, really
more like a block and a half. This means any plenum needs to be
measured and cut outside, taken into the crawl space and assembled
there. Not an ideal situation.

I did try something the othter day and am waiting to see what real
difference it makes. When they put the furnace and AC in almost 10
years ago they sort of jury rigged a setup so I can put my filters in
the return line. At the time I had the non-replaceable things that you
take out and wash. To accomplish this they cut a "door" in the side of
the plenum and would place two filters inside so they looked like a
"V". This access door is 18"x18" and somebody at work suggested to try
and just open that door to make sure I dont have any back pressure. I
did this the other night and the flow from the supply lines did seem to
increase some, but unless I do more evealuation I'm not sure just how
much.

Well this is where I'm at for now. The contractor who came out is
suppose to give me an estimate for new/upgraded duct and different
outside unit.

Oh one more question.. So I dont sound like an idiot when I call other
contractors do I just say I'd like someone to do a heat loss/gain
evaluation on my house.

Time for work..

Greg
PS thanks for the advice so far.. I WAS going to post on alt.hvac, but
after reading some stuff there I didn't think it would be wise. (mom
always alwasy said if ya cant say something nice...)

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