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Old 05-01-2010, 10:51 AM   #1
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Proper technique?


In another forum, it was suggested that without using gauges, a homeowner could determine if charge was low by 'taping' thermometers to the high and low lines and recording the individual temperatures.

I am familiar with the principles of SH & SC and realize that pressure readings are required. Is there any way that proper charge can be determined by using the 2 temperatures, only?

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Old 05-01-2010, 11:25 AM   #2
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Proper technique?


even simpler take supply air temp vs. return air temp if you have 16 to 20 degrees differance your likely ok


Last edited by kennzz05; 05-01-2010 at 11:58 AM.
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Old 05-01-2010, 11:35 AM   #3
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Proper technique?


16 is not uncommon with the more powerful ecm blowers in new furnaces. I get a LOT of them running 16 degF Delta T and 18-20 on the old school units with fixed orifices and slower and smaller fans. The only correct way to charge a system accurately is by weighing in the charge according to line length and manufacturers specs. Reading a superheat or subcooling chart the manufacturers always factor in +/- values so using thermometers is never going to be 100% accurate. Works well enough 95% or more of the time but TX valves modulate and lines temps modulate with it. Airflow and cleanliness or both coils can affect the readings. Beer can cold can be usefull also.
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Last edited by yuri; 05-01-2010 at 12:10 PM.
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Old 05-01-2010, 01:17 PM   #4
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Proper technique?


With the large number of approved coil matches to outdoor units. And the effect it has on operating parameters.
Line temps alone. Are about as accurate as holding your hand over he closest supply register.

EG: 85 outdoor temp. 78 indoor temp.

52 vapor line, 95 liquid line temp.

Is it an under or over charged 10 SEER, or an over or under charged 14 SEER.
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Old 05-01-2010, 04:24 PM   #5
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Proper technique?


Quote:
Originally Posted by beenthere View Post
With the large number of approved coil matches to outdoor units. And the effect it has on operating parameters.
Line temps alone. Are about as accurate as holding your hand over he closest supply register.

EG: 85 outdoor temp. 78 indoor temp.

52 vapor line, 95 liquid line temp.

Is it an under or over charged 10 SEER, or an over or under charged 14 SEER.
No information given, except that unit is not cooling.

Looking at your (example) temps, I'm guessing they are meaningless.

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Old 05-01-2010, 05:36 PM   #6
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Proper technique?


Yep, they are pretty much useless. They are the line temp readings from a slightly under charged 14 SEER A/C though.

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