I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

OK, I've gotten a better handle on this (better doesn't mean a whole
lot in my case, though).

Here are my stats:

Suction line - 63 psi, line temp is 53.5 deg F
Liquid line - 215 psi, line temp is 163 deg F.
Ambient air at bottom of condenser is 81 deg. F.

(This is after adding about 2 lbs of R22.)

If I get it, the subcool is now about 15 deg, and the superheat is
about 60 deg. But, I don't know how this relates to what I need. How
do I figure that out?


BTW, my system is a 5 ton unit, which is oversized for my house, but
that's what the idiot installed 11 years ago. I have been told that a
3.5 ton unit would be better for my place. I plan on replacing the
whole thing as soon as the money's there; preferably with a
ground-source heat pump.

Joe

On Sat, 09 May 2009 18:30:25 -0400, Joe wrote:

I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

On May 9, 7:17 pm, Joe wrote:
OK, I've gotten a better handle on this (better doesn't mean a whole
lot in my case, though).

Here are my stats:

Suction line - 63 psi, line temp is 53.5 deg F
Liquid line - 215 psi, line temp is 163 deg F.
Ambient air at bottom of condenser is 81 deg. F.

(This is after adding about 2 lbs of R22.)

If I get it, the subcool is now about 15 deg, and the superheat is
about 60 deg. But, I don't know how this relates to what I need. How
do I figure that out?

BTW, my system is a 5 ton unit, which is oversized for my house, but
that's what the idiot installed 11 years ago. I have been told that a
3.5 ton unit would be better for my place. I plan on replacing the
whole thing as soon as the money's there; preferably with a
ground-source heat pump.

Joe

On Sat, 09 May 2009 18:30:25 -0400, Joe wrote:
I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

Not enough information Joe. What type of high side to cold side
regulation device does this system have; is is a capillary tube, or
thermal expansion valve system?

From your data I would assume capillary tube control, you need to look
up the temp. vs pressure tables for R22. You want to shoot for, at
minimum thermal load, and saturated suction pressure that is near or
above freezing to prevent your evaporator from freezing up. The
problem is if that is the operating condition. With this type of
"expansion regultor" slightly undercharged systems can freeze the
evaporator, overcharged systems will not be cold enough to remove heat
quickly. Measure the suction line temperature at the air handling
unit, and try to shoot for 38-42 degrees F operating temp. with light
load. If it frosts up, add more refrigerant. If too warm, dump some
back into your tank.
One question would be how low on charge was this, it may have sucked
air into the system if too low and as you indicate the leak on the low
side, this could be a problem if ANY air has gotten into the system.
Along with is water vapor, and this would be a very bad thing if you
don't have a dryer installed.
ignator

ignator wrote:
On May 9, 7:17 pm, Joe wrote:
OK, I've gotten a better handle on this (better doesn't mean a whole
lot in my case, though).

Here are my stats:

Suction line - 63 psi, line temp is 53.5 deg F
Liquid line - 215 psi, line temp is 163 deg F.
Ambient air at bottom of condenser is 81 deg. F.

(This is after adding about 2 lbs of R22.)
I would stop adding refrigerant here. When
outdoor temps get into the upper 90's, the high
side pressure will be 250 or higher. That liquid
line temp is really high, especially for a
relatively new unit. I'd check for dirt in the
condenser. I have to wash crud out almost every
year with a highly focused water spray, and it
makes a huge difference in performance. (I have a
pair of 33 year old Bryant ultra-cheapo units that
I'm babying along until one blows the big one,
which can't be long off.)
What is the outlet air temperature from the
evaporator?

JOn

Joe wrote:
I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

Don't know all that much about superheat and saturation temps , but when
mine got low from a return line leak (second season of use is when it showed
up) I put a clamp-on ampmeter on the compressor lead and charged it until it
read rated amps . I did have gauges hooked up , but can't remember now what
the exact readings were , but it's run flawlessly now for 8 or 9 years
without touching anything but the condensate drain line .
--
Snag
Daddy was an AC&R man ... after he retired from being an ET .

Joe wrote:

I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.


With cars, monitoring the outlet temperature as one adds refrigerant seems to work.
Coldest is best.

Spraying water on the condensor is a subsitute for a big fan. A warm day is optimum for
trying this shortcut.



Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

On Sun, 10 May 2009 00:09:51 -0500, Jon Elson
wrote:

ignator wrote:
On May 9, 7:17 pm, Joe wrote:
OK, I've gotten a better handle on this (better doesn't mean a whole
lot in my case, though).

Here are my stats:

Suction line - 63 psi, line temp is 53.5 deg F
Liquid line - 215 psi, line temp is 163 deg F.
Ambient air at bottom of condenser is 81 deg. F.

(This is after adding about 2 lbs of R22.)
I would stop adding refrigerant here. When
outdoor temps get into the upper 90's, the high
side pressure will be 250 or higher. That liquid
line temp is really high, especially for a
relatively new unit. I'd check for dirt in the
condenser. I have to wash crud out almost every
year with a highly focused water spray, and it
makes a huge difference in performance. (I have a
pair of 33 year old Bryant ultra-cheapo units that
I'm babying along until one blows the big one,
which can't be long off.)
What is the outlet air temperature from the
evaporator?

JOn

Thanks, Jon. The outlet from a register close to the air handler ended
up being at 63 deg, with the incoming (room) air at 75. This was in
the evening, when things outside were beginning to cool down. Does
that seem cool enough?

Eleven YO is a relatively new unit? It's funny how the A/C contractors
who come here tell me it's way past its prime. You don't suppose they
are possesed by ulterior motives, do you?

I will spray the condenser coils this afternoon; I hadn't thought of
that in a while.

Joe

On Sat, 9 May 2009 19:05:46 -0700 (PDT), ignator
wrote:

On May 9, 7:17 pm, Joe wrote:
OK, I've gotten a better handle on this (better doesn't mean a whole
lot in my case, though).

Here are my stats:

Suction line - 63 psi, line temp is 53.5 deg F
Liquid line - 215 psi, line temp is 163 deg F.
Ambient air at bottom of condenser is 81 deg. F.

(This is after adding about 2 lbs of R22.)

If I get it, the subcool is now about 15 deg, and the superheat is
about 60 deg. But, I don't know how this relates to what I need. How
do I figure that out?

BTW, my system is a 5 ton unit, which is oversized for my house, but
that's what the idiot installed 11 years ago. I have been told that a
3.5 ton unit would be better for my place. I plan on replacing the
whole thing as soon as the money's there; preferably with a
ground-source heat pump.

Joe

On Sat, 09 May 2009 18:30:25 -0400, Joe wrote:
I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

Not enough information Joe. What type of high side to cold side
regulation device does this system have; is is a capillary tube, or
thermal expansion valve system?

From your data I would assume capillary tube control, you need to look
up the temp. vs pressure tables for R22. You want to shoot for, at
minimum thermal load, and saturated suction pressure that is near or
above freezing to prevent your evaporator from freezing up. The
problem is if that is the operating condition. With this type of
"expansion regultor" slightly undercharged systems can freeze the
evaporator, overcharged systems will not be cold enough to remove heat
quickly. Measure the suction line temperature at the air handling
unit, and try to shoot for 38-42 degrees F operating temp. with light
load. If it frosts up, add more refrigerant. If too warm, dump some
back into your tank.
One question would be how low on charge was this, it may have sucked
air into the system if too low and as you indicate the leak on the low
side, this could be a problem if ANY air has gotten into the system.
Along with is water vapor, and this would be a very bad thing if you
don't have a dryer installed.
ignator

I don't know what type of system I have; I had assumed capillary, but
don't know what to look for. Since the suction line was at 63 psi,
that translates to about 36 deg F, but what constitutes a "light
load"? If the outdoor temp is around 80, is that good enough? Real
summer temps here in the South Carolina "mountains" get to be in the
low-to-mid 90s on many days.

I may have some air in the system, but I think I'm OK. Anticipating
this problem, last fall I shut off the valves in the outside unit to
minimize leakage. Yesterday, there was still a little bit of pressure
in the lines going up into the attic, so I hope it's alright. There is
a dryer installed, as well.

I'll check the line temp at the evaporator as soon as I can.

Thanks for your helpful reply, BTW.

Joe

Terry Coombs wrote:

Joe wrote:
I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system repaired, I
need to add a charge. I've got the gauges hooked up, and measured the
ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

Don't know all that much about superheat and saturation temps , but when
mine got low from a return line leak (second season of use is when it showed
up) I put a clamp-on ampmeter on the compressor lead and charged it until it
read rated amps . I did have gauges hooked up , but can't remember now what
the exact readings were , but it's run flawlessly now for 8 or 9 years
without touching anything but the condensate drain line .
--
Snag
Daddy was an AC&R man ... after he retired from being an ET .


He was an Extra Terrestrial? Wow! ;-)


--
You can't have a sense of humor, if you have no sense!

Michael A. Terrell wrote:
Terry Coombs wrote:

Joe wrote:
I have a small leak in my evaporator. So, here comes the cooling
season again, and until I have the money to get the system
repaired, I need to add a charge. I've got the gauges hooked up,
and measured the ambient temperature at 82 deg F.

I remember that I used to just subtract x deg. from the ambient, and
add refrigerant until I reached that value on the low-side gauge.
However, I don't remember what that value is. IIRC, it was 35 or 40,
but the synapses don't fire like they used to.

Can anyone help me out here? I fail to understand the
superheat/subcool stuff, but the rule-of-thumb has served me well in
the past.

Joe

Don't know all that much about superheat and saturation temps ,
but when mine got low from a return line leak (second season of use
is when it showed up) I put a clamp-on ampmeter on the compressor
lead and charged it until it read rated amps . I did have gauges
hooked up , but can't remember now what the exact readings were ,
but it's run flawlessly now for 8 or 9 years without touching
anything but the condensate drain line .
--
Snag
Daddy was an AC&R man ... after he retired from being an ET .


He was an Extra Terrestrial? Wow! ;-)

No , no , no , he was an Electronics Tech ! Worked at HAFB for something
like 26 years in an electronics test eqpt repair shop , forced retirement in
'78 due to a broken hip ca 1964 (slipped on a loading dock at Malmstrom
AFB). Dad was one of the first people (AFAIK) to be trained to repair CNC
machinery for the Air Force . He also worked in Minuteman silo's , and did a
lot of other things he never talked about ... he got to ride in some very
fast aircraft from time to time , when there was "a problem we need you to
look at , Dick" .
Dad was one of the most intelligent people I ever knew , and I wish I knew
a tenth of what he did ...
--
Snag
Been gone ten years now ...

Terry Coombs wrote:

Michael A. Terrell wrote:

He was an Extra Terrestrial? Wow! ;-)

No, no, no, he was an Electronics Tech! Worked at HAFB for something
like 26 years in an electronics test eqpt repair shop, forced retirement in
'78 due to a broken hip ca 1964 (slipped on a loading dock at Malmstrom
AFB). Dad was one of the first people (AFAIK) to be trained to repair CNC
machinery for the Air Force. He also worked in Minuteman silos, and did a
lot of other things he never talked about... he got to ride in some very
fast aircraft from time to time, when there was "a problem we need you to
look at, Dick".
Dad was one of the most intelligent people I ever knew, and I wish I knew
a tenth of what he did ...
--
Snag
Been gone ten years now ...


You will always miss him. I've lost both family, and close friends
over the years. I think of one or more of them several times a week.

As far as ET = Electronics Tech, I try to avoid the confusion by just
saying I'm an Electronics Tech, Electronic Engineering Tech, or
Broadcast Engineer. In a few months it will be 44 years, including the
time I worked as a Broadcast Engineer in the US Army for AFRTS. I
tested out of the three year engineering school, and got dumped into a
really screwed up radio & TV station in the middle of nowhere. Over the
years I worked in almost every area of electronics, including avionics.
(A communications system for the ISS, along with the telemetry equipment
that tracks the Space Shuttle missions. That was a cool job.

BTW, Just think how much smarter he would have been if he was an
Extra Terrestrial! ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

http://www.flickr.com/photos/materrell/

"Joe" wrote in message
...
I have a small leak in my evaporator.

Block off the fan discharge of the condensing unit until the liquid line
temperature runs at 100F to 110F. Then shoot for 10-15 degrees subcooling.
It will be reasonably close. Far better than ambient plus 30 degrees or any
other rule of thumb!
Greg