Nominal Low Pressure Range for Freon Charge?

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Old 08-14-13, 12:35 PM
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Nominal Low Pressure Range for Freon Charge?

What is a nominal Low Pressure range when charging the following HVAC unit?
Nordyne-Gibson JS3BC-042KA, 3.5 ton. Inspection plate indicates unit was designed for R22 at 150 psi low range and 400 psi high range. However, an AC technician indicated 75 psi was a good low pressure range, (high range was not obtained). The unit does not cool as well as it did last summer during the same climatic conditions. And I can’t help but wonder if the charge pressure is too low. Although, 75 psi does fall just within the liquid-vapor Ph curve for R22. Please share your thoughts (the more technical the better, please).
 
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Old 08-14-13, 12:50 PM
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I have to retract the statement as to where the 75 psi falls on the Ph curve because of inadequate data.
 
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Old 08-14-13, 02:43 PM
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NOPE! Can't answer that question! Please read forum rules....http://www.doityourself.com/forum/ai...ng-your-c.html
 
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Old 08-14-13, 02:48 PM
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Thats a valid question according to the sticky... He is only asking about pressures...


General questions on what the effects of too much refrigerant or too little refrigerant in the case your system is freezing or a tech added refrigerant and it's not performing properly are welcome but repair remedies will not be given if it pertains to the refrigerant circuit. We will tell you what to look out for when a tech is working on your unit but no step by step or technical information.

Read more: http://www.doityourself.com/forum/ai...#ixzz2byzfHlp2



http://www.doityourself.com/forum/ai...ng-your-c.html


To the OP I cant answer since I am not an HVAC tech... Perhaps one of the pros will guide you..
 
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Old 08-14-13, 04:59 PM
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There are many variables that are used to determine if a unit is properly charged or is working at full capacity. Just knowing the low side pressure is not nearly enough to know.
 
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Old 08-15-13, 06:01 PM
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Yeah, I had previously read the Sticky Notes before posting my question and the nature of my question was to try and understand why the Tech thought 75 psig on the low side was adequate and I had no intention of charging the unit myself.

Yes, it takes more than just the low side pressure reading to determine if a unit is working at full capacity; but, that is not my focus at the moment. Later yes, but I wanted to resolve the low pressure question first and I think the nature of the question can be isolated from an “entire system perspective” for the moment. Information not consistent with forum rules has been removed. Unedited post archived.
 

Last edited by ray2047; 08-15-13 at 06:19 PM.
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Old 08-15-13, 06:36 PM
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With the information given, we have no way to know if the 75# is a "good pressure" or not. 75# under some conditions could be low yet under other conditions it could be high.
If he charged the system to a low side pressure of 75# without even checking the high side, you'd better find a new tech.
 
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