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  1. #40
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    Sep 2008
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    Quote Originally Posted by GT1980 View Post
    if pumping into the cdsr, it changes - higher only a little, enough to fill the cdsr.

    eh?
    What you also have to consider here is the location of the "restriction"

    When you're pumping down a unit, you are emptying the liquid line of refrigerant, adding MORE REFRIGERANT to the condenser than you would in the case of a metering device shut down which would leave the liquid line full.

    This could conceivably cause a higher head pressure rather than a lower pressure, which is what one would "theoretically" get.

  2. #41
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    Quote Originally Posted by Frostmonkey74 View Post
    When you pump a system down by front seating the king vale on the receiver the gauge port on the king valve is still on the high side if the system. ( refrigeration condensing unit not AC/heat pump unit) so there for is still sensing high side pressure..
    Remember that a great many techs have never worked on a refrigeration unit with a discharge service valve.

  3. #42
    Join Date
    Nov 2006
    Location
    Southeastern Pa
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    19,497
    The other aspect is that the compressor is then radiating heat toward that condenser, and often it is in an enclosed space without the proper ventilation (under a bar cabinet, or an enclosed island salad bar, or even a hot kitchen) which will raise the temp and pressure of the refrigerant you discussed.

    Further, I have never found a clean condenser, unless I serviced it the day before. So the fan may not be moving enough air to keep the heat from the compressor from raising the pressure of the refrigerant.

    There are a lot of factors that are not ideal that affect systems with problems. And, compressors always have refrigerant in the cylinders due to the area at the top where it cannot be forced out. So, it is continuously expanded and compressed with every stroke, making pressure at the output of the compressor while it is running, even when all of the low side volume has been consumed. In order to raise the pressure at that point, you would indeed have to add more refrigerant for it to compress, and that would be the overcharge mentioned by others earlier in this thread.

    We would need to know how much of a charge was forced into the condenser, and how hot that charge is due to environment and radiant heat from the compressor shell, in oder to predict the pressure you would find on the high side with a cap tube restriction.

    Then there is a restriction in a cap tube that is not 100%...

    Shall we continue?
    [Avatar photo from a Florida training accident. Everyone walked away.]
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  4. #43
    Join Date
    Jul 2013
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    63
    Quote Originally Posted by Frostmonkey74 View Post
    When you pump a system down by front seating the king vale on the receiver the gauge port on the king valve is still on the high side if the system. ( refrigeration condensing unit not AC/heat pump unit) so there for is still sensing high side pressure..
    Gotcha. I was thinking heat pump or ac.

  5. #44
    Join Date
    Jul 2013
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    63
    I'm still going to argue that a slight restriction Causes high heads. It's goes against what were taught and what the books say but high head low suction is a classic sign of a partial restriction in a system. I've seen it argued on here before and you have the guys who go and read and say low head and the guys who go off what they are and say or can cause a high head.

  6. #45
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    Feb 2006
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    USA
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    Quote Originally Posted by Tommyz23 View Post
    I'm still going to argue that a slight restriction Causes high heads. It's goes against what were taught and what the books say but high head low suction is a classic sign of a partial restriction in a system. I've seen it argued on here before and you have the guys who go and read and say low head and the guys who go off what they are and say or can cause a high head.
    I encounter multiple restrictions on a monthly basis. Grant it I don't do residential but I occasionally encounter a spilt system. A restriction is a restriction. A properly charged system with a restriction in or upstream of the liquid line will show a low suction and a low head. My eyes, gauges and many years of doing this know that as do many guys here

    Sent from my SGH-T999L using Tapatalk 2

  7. #46
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    Jul 2013
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    63
    Quote Originally Posted by hvac wiz 79 View Post
    I encounter multiple restrictions on a monthly basis. Grant it I don't do residential but I occasionally encounter a spilt system. A restriction is a restriction. A properly charged system with a restriction in or upstream of the liquid line will show a low suction and a low head. My eyes, gauges and many years of doing this know that as do many guys here

    Sent from my SGH-T999L using Tapatalk 2
    I see both but you know how residential can be. I've never see the system before and neither has my company and I have a high head low suction. Package units are great.

  8. #47
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    Jun 2013
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    NORTHERN
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    Quote Originally Posted by Tommyz23 View Post
    I see both ....have a high head low suction. Package units are great.
    Comm and Inds and a few chillers, and 'lotta chillers called GeoThermal Ht P, and just 'chillers' that have no rev valve at all that are in R/A of quick install drop-ins- for lowest amortized return$$$ period heating a spce vs. oil/Propane/Elect-scorched air...

    Pumped by compressor raises pressure a lot of what's REM: those into out door condensers or the indoor chillers that heat a space (comm and res) , right off to the packaged cdsr: Pumped just heats a little, heads discharge up a bit to even relatively higher than expected in other than other comm rfg.
    ... however, much work still needs to be done.
    CLOSED LOOP newer ratings are listed, but in numerical EER's Closed- is posted below OPEN LOOP EER's:

    http://www.energystar.gov/productfin...r=0&lastpage=1

  9. #48
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    Jul 2010
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    Quote Originally Posted by GT1980 View Post
    Comm and Inds and a few chillers, and 'lotta chillers called GeoThermal Ht P, and just 'chillers' that have no rev valve at all that are in R/A of quick install drop-ins- for lowest amortized return$$$ period heating a spce vs. oil/Propane/Elect-scorched air...

    Pumped by compressor raises pressure a lot of what's REM: those into out door condensers or the indoor chillers that heat a space (comm and res) , right off to the packaged cdsr: Pumped just heats a little, heads discharge up a bit to even relatively higher than expected in other than other comm rfg.
    Does anyone have any idea what this guy just said?

  10. #49
    Join Date
    Jul 2011
    Location
    Nanaimo,BC, Canada!
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    346
    Nope.

  11. #50
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    Sep 2002
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    2,887
    Quote Originally Posted by Brian8383 View Post
    Does anyone have any idea what this guy just said?
    I think he's trying to sell us a chiller!

  12. #51
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    Sep 2002
    Location
    Virginia
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    3,325
    i read it twice .... i think my brain is tied into a knot now

  13. #52
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    Jul 2009
    Location
    new york
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    Quote Originally Posted by Snapperhead View Post
    i read it twice .... i think my brain is tied into a knot now
    I agree with you - both pressures will be low. The suction will be very low and the discharge pressure just a little low. The reason people think the high side will rise is because the refrigerant pile up in the condenser. However, since it is not going anywhere, it just sits there as long as there is a reasonable amount of space. The condenser in most systems can hold all of the system refrigerant. However, if someone tries to "fix" the restriction by adding refrigerant, you can fill up the condenser and the high side pressure will rise. This can also happen with long line sets. The best way to tell the difference between an undercharge and a restiction is looking at the subcooling.An undercharged system will have a low subcooling while a system with a restriction will have a high subcooling. Both will have a high superheat.

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