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Old Yesterday, 11:04 AM   #1
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One Degree Subcooling


Inside temp split 12 degrees when i started using ac this year. I keep a thermometer in a vent and have observed this split to be 16 to 20 degrees for several years. Condensor coil appeared clean but I hosed backwards through the fins anyway. Did not make any difference. While I did not inspect evap coil, I believe it to be clean. Airflow seems normal.

410a split system with txv 4 ton
85 ambient
Gauges showed:
Suction line 90psig suc line temp 55
Liquid line 290psig liq line temp 92.3

I make this to be 1 degree SC (as near as I can read the gauge) and ~30 degrees SH. I conclude (maybe incorrectly) that low SC and high SH means low charge.

Added refrigerant...less than one pound. Liq line pressure now 300 but liq line temp now 96...still little to no SC. Inside temp split improved to 16.

When I saw no change in SC I stopped...afraid of overcharging.

Time for some help from the experts.

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Old Yesterday, 11:23 AM   #2
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One Degree Subcooling


It still could be undercharged as everything is heading in the right direction. Did your superheat come down any? Do you have a way of heating the TXV sensing bulb while monitoring your readings?

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Old Yesterday, 11:26 AM   #3
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Give it 10 - 15 min. then check subcooling again.
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Old Yesterday, 12:13 PM   #4
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One Degree Subcooling


TXV - carefully take the remote sensing bulb loose from the copper refrigeration line it is connected / strapped to . ( This would be a good time to visually inspect the evaporator coil & clean if necessary . )

Have a friend insert the remote sensing bulb into warm water or hold it in his / her hand until it reaches approximately body temperature .

While this is taking place , watch your pressures and temperatures . Report back with info / data .

God bless
Wyr

Last edited by WyrTwister; Yesterday at 12:16 PM.
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Old Yesterday, 12:17 PM   #5
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One Degree Subcooling


85 outside, 13 SEER R410A, normally has a head pressure somewhere around 340PSIG. What was your SH and suction pressure.

A wet condenser coil takes 15 minutes or so to completely dry.
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Old Yesterday, 12:31 PM   #6
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Please pardon me , I am confused .

The pressure chart I downloaded indicates R410a , at 85F , has a boiling point of around 255 PSI . I would have thought the head pressure would be 10F - 15F ( no more than 20F ) more than that ?

Please try to explain to this old , fat DIY'er what is going on . I know , sometimes I can be slow on the uptake , but I find HVAC interesting and really wish to learn .

Thanks :-)
God bless
Wyr

Please pardon me again . After studying the chart again , the light bulb flashed on ! A 15F difference gives you almost precisely 340 PSI . Right on the button , to what you predicted ! :-)

Thanks again .

Last edited by WyrTwister; Yesterday at 12:39 PM.
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Old Yesterday, 03:57 PM   #7
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OP here. Thank you very much for the replies. Took advice and ran system for a longer period of time and took more data.

92 ambient
77 inside @52% RH

After 15 minutes:
Suc pressure 107 suc line temp 72
Liquid line pressure 315 liquid line temp 96

after 25 minutes
suc pressure 110 suc line temp 74
liquid line pressure 335 liquid line temp 99.5

after 40 minutes
suc press 107 suc line temp 73
liquid line pressure 320 liquid line temp 97

After 45 minutes I had to disconnect due to an approaching thunderstorm but the pressures were slowly creeping up again.

The period of these P/T changes was about 10 to 15 minutes. Are these P/T swings normal or is something else going on ?

Even at the best readings, still looks like SC is low and SH is high.

Sorry, I have not checked the txv per instructions due to lack of help and a very hot attic.

Thanks again for the responses.
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Old Yesterday, 04:06 PM   #8
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One Degree Subcooling


Its still low on charge. Or you have a restriction or TXV that isn't functioning correctly.

Most likely its low on charge. The readings changed as the air temp of the return came down, and it as able to feed more liquid to the evap.

It needs more refrigerant.
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Old Yesterday, 04:19 PM   #9
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What Bitters meant was to give the system 15 minutes to stabilize when first starting up or after making any changes such as adjusting the freon charge. Then take note of the measurements.
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Old Yesterday, 05:12 PM   #10
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Quote:
Originally Posted by tyeboe View Post
OP here. Thank you very much for the replies. Took advice and ran system for a longer period of time and took more data.

92 ambient
77 inside @52% RH

After 15 minutes:
Suc pressure 107 suc line temp 72
Liquid line pressure 315 liquid line temp 96

after 25 minutes
suc pressure 110 suc line temp 74
liquid line pressure 335 liquid line temp 99.5

after 40 minutes
suc press 107 suc line temp 73
liquid line pressure 320 liquid line temp 97

After 45 minutes I had to disconnect due to an approaching thunderstorm but the pressures were slowly creeping up again.

The period of these P/T changes was about 10 to 15 minutes. Are these P/T swings normal or is something else going on ?

Even at the best readings, still looks like SC is low and SH is high.

Sorry, I have not checked the txv per instructions due to lack of help and a very hot attic.

Thanks again for the responses.

Which is precisely why I do not want an air handler / furnace in an attic . :-(

My attic is too " low " anyway . I sacrificed 2 small back to back closets to make our furnace closet .

God bless
Wyr

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