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Thread: Gauge Reading

  1. #1
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    May 2005
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    Gauge Reading

    Ok yeah Im not that good at reading my gauges, I admit that, but here goes. R22, 91*ambient, suction 75#, discharge 300#, low on refrigerant? Im only getting about 60* DA temp. Room temp is about 76, sorry, didnt get RA temp. And for future reference, the temp readings on the gauges, what do they correspond to? The suction temp is the evaporator temp, correct? And on the discharge side is ambient plus 20*?
    A lack of planning on your part does not constitute a state of emergency on my part.

  2. #2
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    Temps on your gauge are saturation temps for a given refer. Yes suction line is out of evaporator.

  3. #3
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    the temperature scale on your gauges show the refrigerant temperatue at saturation.

    the only reason to connect a set of gauges is to read saturation temps. stop thinking of them as pressure gauges. they're not. they're saturation temperature gauges.

    need way more info to help with this particular problem
    my boss thinks its possible to repeal the laws of physics

  4. #4
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    None of the pressures you posted indicate a system is short on refrigerant with the outdoor and indoor temperatures given. It may not be cooling well, I suspect refrigerant levels aren't the issue.

    Liquid line side can be ambient +15 for some of the modern high efficiency systems and ambient +30 for some of the ancient ac systems. Ambient plus 20 or 25 isn't bad for many 13 or 14 seer systems. Look to the manufactures data and correlate those pressures to point you in the right direction.. Superheat and sub-cooling will to tell you what is happening along with the pressures.

    The 300 psi correlates with a condensing P/T of 130 degrees. A bit high for a 91 degree ambient. I'd check the condenser coils and make sure they're clean. Check to make sure you don't have a two coil system (one behind the other). In time, these will catch dirt between the 1st and second coil, making a thin blanket that reduces the air volume through the coil. They look clean and aren't. This leads to a higher condenser temperature like what you're seeing. The liquid line is usually hot to the touch too.

    The double coil systems are connected together at one end with clips, zip ties or even a small metal link. Remove those links and gently spread the coils apart and wash between them. You'll have to disconnect power and possibly remove hail guards, condenser fan and condenser top to get the job done. Every system is a little different, some are really time consuming to do. After getting it clean, push the coils gently together, refasten and reassemble.

    These get to be easy once you've done five or six of them.
    Last edited by allan38; 06-11-2013 at 10:23 PM.
    “I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.”
    ― Benjamin Franklin

  5. #5
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    Quote Originally Posted by ch4man View Post
    the temperature scale on your gauges show the refrigerant temperatue at saturation.

    the only reason to connect a set of gauges is to read saturation temps. stop thinking of them as pressure gauges. they're not. they're saturation temperature gauges.
    Excellent way to look at them!
    “I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.”
    ― Benjamin Franklin

  6. #6
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    X2 on the condensing coil clean. super heat and subcool are your buds

  7. #7
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    That's another thing...I have never reallyunderstood sh/sc...can someone splain it in english?

  8. #8
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    SH is heat above the sat temp, usually taken just down stream of the compressor or outlet of evaporator. SC is temperature below sat temp usually taken on the high side just befor the expansion device or out of the condenser.

  9. #9
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    You'll need an accurate (and convenient) way of measuring pipe temperatures. A couple clamp thermometers are what most pros use.

    This is crucial for measuring SH and SC.

    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    Wayne Pendergast, efficientcomfort.net

  10. #10
    Join Date
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    A good example is a 7.5 ton system I had earlier this week.

    Other hvac company wrote on their invoice "Systems freon pressures normal". So the customer assumed the freon was ok and I should look elsewhere.

    The main complaint was humidity problems in the building.

    I corrected the systems charge going from a subcooling of 26* to 13*, way overcharged. They called just today to say it feels much much better in there. Pressures were good to look at, but meant little in knowing what it was actually doing.

  11. #11
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    Study refrigeration theory if you can like take some community college classes if possible it would help and you'll learn alot

  12. #12
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    Jun 2013
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    When a liquid evaporates it absorbs heat and when a vapor condenses it rejects heat and refrigerant has a pressure and temp. Relationship so when refrrigerant evaporates in the evap your measuring the amount of heat added after evaporation with superheat and vise versa in the condensor your measuring the amount of heat rejected from the vapor that was condensed into a liquid after it condenses at a certain pressure

  13. #13
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    Jun 2013
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    * with subcooling

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