I read a article by Jim Wheeler on subcooling considerations. He states that a unit with a TXV should have atleast 10* of subcooling, but to achieve even greater efficiency charge until the liguid line temp. reaches the outside temp. or until you notice a significant rise in head pressure whichever comes first. I have a Rheem 12 seer 3 ton system with a TXV. I added refrigerant until the liq. line temp dropped to 98*. Outside temp. was 95*. Liq. line pressure was 295. That gave me about 31* of subcool. Is this system over charged or is it more efficient?
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Its sounds like you over charged it.
Did the temp delta across your coil increase?
head pressure kinda high i think... maybe a 200 sounds better..
When you charge it SC method and the liquid line temp. rises and then starts to drop as your charging then to me you have it overcharged, SC you just subtract the reading on you high side gauge from liquid line temp and I try for anywhere from 10-13 degree difference and leave it alone.
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The Delta T did not increase still at 20* split
You are definitely overcharged with that type of sub-cooling. Next subject - high head pressure trips.
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what's the low side at?
seems to me the only thing that's happening is the compressor is working harder just to lose that heat in the condensor.
...that's another thing , what's the compressor amp draw?
[Edited by wolfstrike on 08-15-2006 at 07:10 AM]
The amp draw on the compressor is about 13 amps
usually newer units have the subcooling rating stamped on the name plate.
31 degrees is overcharged. the highest i have ever seen is 18 but usually 10.
but if your not sure just install a sightglass then put a false load like if it were 95 degrees outside and when it clears you should be close
You don't charge to a clear sight glass on residential systems. You will overcharged.
coach...you need to register as a pro. This topic needs to be discussed in the professional forum.
Please register as a PRO, and this thread will be moved to the PRO area.
Perhaps you should have read the instructions before calling.
This is the article I read on SUBCOOLING. My question is by charging the system to achieve more subcooling are you over charging the system or is it more efficient like the article says?
Subcooling occurs when the
temperature of the refrigerant in the
liquid line is lowered below its
saturation point. When refrigerant is
subcooled, there is less heat content as
it enters the metering devise and thus,
more cooling is possible. Most
modern equipment is designed to
provide 10 or more degrees of
subcooling, by using larger condensers
or by addition of subcooling coils.
So after adding refrigerant to clear
the liquid line sight glass at normal
temperatures, you must add more
refrigerant to provide the necessary
subcooling. If you fail to do this, the
equipment will not work to capacity
and further losses due to liquid line
“flashing” will occur.
Subcooling charging method
The amount of subcooling can be
determined by checking the liquid line
temperature and then comparing it to
the saturated condenser temperature as
read on a high side gauge. As an
example: A head pressure of 250 psig
yields a saturated temperature of
117*F [using a refrigerant pressuretemperature
chart or from the gauge
Charging until the liquid line
temperature leaving the condenser is
107*F [in our example] assures at
least 10* subcooling [117-107=10].
This [10*] is the amount of subcooling
specified for many systems, and it will
seldom get you in trouble.
However, to achieve even greater
efficiencies on some systems [where
subcooling circuits are large enough],
charge until the liquid line temperature
at the metering device equals the
outdoor temperature. Since condenser
coils are less than 100% efficient, the
refrigerant temperature leaving the
condenser will never equal the outdoor
ambient, but a liquid line that is
sufficiently long and which runs
through a cooler outdoor ambient may
be used to provide additional
subcooling. You can then achieve
maximum efficiency by adding
refrigerant to cool this line, until you
note some significant rise in head
pressure or until the line temperature
reaches outdoor ambient, whichever