Home Ownership (misc.consumers.house)

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Old May 22nd 04, 11:17 AM
unix-freak
 
Posts: n/a
Default AC Advice Needed!

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 foor home. I have a 3 ton unit now. It's
a Trane and the house is 21 years old.

  #3   Report Post  
Old May 22nd 04, 05:37 PM
John Davies
 
Posts: n/a
Default AC Advice Needed!

On 22 May 2004 03:17:56 -0700, (unix-freak)
wrote:

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.


Pardon me, but what are you trying to say? Are you measuring the temp
of the condensor cooling fan air or what? The important temp is the
air coming off the evaporator coil into your ductwork - what is that
value?

There is 3 feet above the deck. He checked the
charge and said it was good.


What were the pressures measured at the compressor? You can have
plenty of freon and the system still may not work if you have a
plugged expansion valve or other easy-to-fix problem.

Inside supply air was 70 degrees.


Air coming out of the registers?

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


150 in the attic? No wonder your house is warm inside. Get some
adequate ventialtion and fix that vent fan and then see how your
system does.

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


I live in a hot (not blistering) climate in Eastern Washington. My a/c
is a 5 ton, but I have 4500 sq ft. Unless you live in the SW desert I
don't see how you need a 5T unit in an 1800 sq ft house. I second the
comment that your duct system won't work if you double the size of the
a/c and air handler.

Talk to at least two more reliable contractors before acting. And get
that attic temp down first.



John Davies
http://home.comcast.net/~johnedavies/
'96 Lexus LX450
'00 Audi A4 1.8T quattro
Spokane WA USA
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Old May 23rd 04, 01:10 AM
unix-freak
 
Posts: n/a
Default AC Advice Needed!


"John Davies" wrote in message
...
On 22 May 2004 03:17:56 -0700, (unix-freak)
wrote:

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.


Pardon me, but what are you trying to say? Are you measuring the temp
of the condensor cooling fan air or what? The important temp is the
air coming off the evaporator coil into your ductwork - what is that
value?


Yes. The air temp was measured at the compressor just to see if there was
too much air getting trapped under the deck.

A couple of days ago it was 80 outside. I measured 78 into the condensor
coil and at the plenum after the coil was 68.


There is 3 feet above the deck. He checked the
charge and said it was good.


What were the pressures measured at the compressor? You can have
plenty of freon and the system still may not work if you have a
plugged expansion valve or other easy-to-fix problem.


I don't remember. I think the high side was at 200 lbs.

Inside supply air was 70 degrees.


Air coming out of the registers?

Yes.


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


150 in the attic? No wonder your house is warm inside. Get some
adequate ventialtion and fix that vent fan and then see how your
system does.


I just replaced the fan an hour ago.

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


I live in a hot (not blistering) climate in Eastern Washington. My a/c
is a 5 ton, but I have 4500 sq ft. Unless you live in the SW desert I
don't see how you need a 5T unit in an 1800 sq ft house. I second the
comment that your duct system won't work if you double the size of the
a/c and air handler.

Talk to at least two more reliable contractors before acting. And get
that attic temp down first.



John Davies
http://home.comcast.net/~johnedavies/
'96 Lexus LX450
'00 Audi A4 1.8T quattro
Spokane WA USA





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Old May 23rd 04, 02:18 PM
Travis Jordan
 
Posts: n/a
Default AC Advice Needed!

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 foor 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.

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


  #7   Report Post  
Old May 23rd 04, 07:07 PM
unix-freak
 
Posts: n/a
Default AC Advice Needed!


"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.


  #8   Report Post  
Old May 23rd 04, 09:25 PM
Travis Jordan
 
Posts: n/a
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.


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Old May 23rd 04, 09:56 PM
unix-freak
 
Posts: n/a
Default AC Advice Needed!


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

Yeah...that's what I meant. I actually opened up the plenum and there's
plenty of water. I didn't do anything as far as coil cleaning. I guess I
could spray it down with the proper coil cleaner. I also made sure that the
PVC wasn't clogged while I was there.

The most common causes of low delta-T a

1) undercharged refrigerant due to a leak

I had a different tech out last summer and he said that the charge was fine,
so that's 2 techs that have had their guages on it saying it's fine.


2) excessive air flow over evaporator (i.e.air handler fan set to wrong
speed)

I double checked it, and it's wired for high with the heater wired for low.

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.


Oh...one more thing. It's 88 outside right now and my compressor just cut
off on it's own even though the fan is still running and the thermostat set
to auto. It did that yesterday and I had to turn off power to it for 10
minutes, then it came back after that. I know in automotive ac, the clutch
with kick off if the charge is low.





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Old May 23rd 04, 10:14 PM
Travis Jordan
 
Posts: n/a
Default AC Advice Needed!

unix-freak wrote:
I assume you mean "There's not much condensation from the evaporator
(inside) coil..."

Yeah...that's what I meant. I actually opened up the plenum and
there's plenty of water. I didn't do anything as far as coil
cleaning. I guess I could spray it down with the proper coil cleaner.
I also made sure that the PVC wasn't clogged while I was there.

The most common causes of low delta-T a

1) undercharged refrigerant due to a leak

I had a different tech out last summer and he said that the charge
was fine, so that's 2 techs that have had their guages on it saying
it's fine.


2) excessive air flow over evaporator (i.e.air handler fan set to
wrong speed)

I double checked it, and it's wired for high with the heater wired
for low.

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.


Oh...one more thing. It's 88 outside right now and my compressor just
cut off on it's own even though the fan is still running and the
thermostat set to auto. It did that yesterday and I had to turn off
power to it for 10 minutes, then it came back after that. I know in
automotive ac, the clutch with kick off if the charge is low.


It is also possible that the compressor is overheating and shutting down
on overtemperature. If the system were just low on refrigerant (and it
had an auto-reset low-pressure switch installed, a feature seen mostly
on high-end systems) then indeed it might restart after 10 minutes. How
ever, I wouldn't risk compressor damage if I were you.

Tomorrow morning call one of the local HVAC distributors and ask the
counter person for the name of a really good technician that they would
have work on their personal system. Johnstone Supply will do if you
have one in the area, or find the distributor for the manufacturer of
your system.




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