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  1. #1
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    Refrigersnt pressures with low ambient temp.

    I've been in the field learning HVAC for a little over a year and still have the hardest time judging whether or not the pressures are correct when the outdoor ambient is around 60-70 degrees. Sometimes I want to say they're low then end up doing a pointless leach search while possibly over charging the system. Any tips that could help me figure this out more accurately?

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  3. #2
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    Mar 2016
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    Checking pressures in cooling

    When checking pressures at the condenser and the outdoor temp is 67 and indoor temp is 75, what is the best way to accurately determine whether or not the system is over charged or low?

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  5. #3
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    Mar 2016
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    Determining refrigerant pressures. Please help.

    I still have the hardest time determining whether a system is over charged or under charged. For example, system with R-22, TXV, temp in the house was 75 and the temp at the condenser was 74. Pressures were 50/165. Split was 17 and subcooling was 23. Brand new filter and clean evaporator. What you guys think?

  6. #4
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    R 22 at 50 psi is about 14°F saturated. Without a suction line temp you don't have all the data needed. If you had 10° to 15° of superheat then you would have a suction line temp of 24 to 30° and coil would be icing up. But it would indicate the txv is doing it's job. Low airflow or dirty coil might be the issue. If you had a 70° suction line then your superheat would be way out of the ballpark at over 50°. This would be many possibilities including restricted filter drier, failed txv. Higher than normal subcooling may support that. You need to get more data.
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  7. #5
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    This is what pisses me off most of the time because when it comes to 22 I've been told to check super heat with a piston and to check subcooling if there is a TXV. Air flow was good, air filter was brand new and coil was clean.

  8. #6
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    Jan 2004
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    Subcool and superheat.
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  9. #7
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    Mar 2016
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    On the subcooling chart located on back panel says to not check subcooling or superheat if ambient temp is lower then 70.

  10. #8
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    At 67 outdoor, its still accurate enough.
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  11. #9
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    Mar 2005
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    Pearland Texas
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    R22 at 50 psi is 26 degrees saturation

  12. #10
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    Jul 2013
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    Quote Originally Posted by flogprousa7368 View Post
    This is what pisses me off most of the time because when it comes to 22 I've been told to check super heat with a piston and to check subcooling if there is a TXV. Air flow was good, air filter was brand new and coil was clean.
    Check system charge by superheat with a piston and by subcooling with a TXV for any refrigerant, not just R22.

    23 degrees subcooling is very high, which would mean a restriction or overcharge. What was your suction line temperature?

  13. #11
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    Jul 2013
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    65 degrees or higher is fine, but if you have a TXV, you can always block the coil/cycle the ODF to drive up the head pressure and simulate a warm day. That's what I do on start-ups in cold weather.

  14. #12
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    Oct 2015
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    Any Fixed type office superheat, txv use sub cooling. The super heat will vary according to conditions, i.e. out side temp and inside temp and humidity. Super heat can range from 0 to well into the 20s, although I will always have some super even when it calls for 0. Manufactures have charts that show superheat required for their units. This is much as We can help you in the general forum.
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  15. #13
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    Quote Originally Posted by flogprousa7368 View Post
    This is what pisses me off most of the time because when it comes to 22 I've been told to check super heat with a piston and to check subcooling if there is a TXV. Air flow was good, air filter was brand new and coil was clean.
    Yes, those are the values you should check if you want to know where the refrigerant is in the system, and if you are reasonably close to a good charge.

    What is it about recording those values that frustrates you?

    Have you been taught how and where to make those measurements, and if so, what were the superheat and subcooling values you measured?
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