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  1. #53
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    Nov 2006
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    Quote Originally Posted by ar_hvac_man View Post
    LOL! Thats wrong TB.

    I know, I know. Sometimes, the morning DJ comes back out....
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    2 Tim 3:16-17

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  2. #54
    Join Date
    Mar 2007
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    NW AR
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    Changed powerhead, no change. Put in the number 4 and shes rockin and rollin

    Thanks guys!

  3. #55
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    May 2004
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  4. #56
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    Jul 2000
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    Guayaquil EC
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    You mean I got it right???

    I've had this happen enough times to make me wonder about the distributor nozzle sizing for Heatcraft (and possibly others). The reasoning is if the nozzle is undersized, there will be a lower available pressure drop across the expansion valve and therefore prevent it's operation at full flow capacity. By upsizing the expansion valve (or its orifice size in this case) you may well correct the flow problem, but not the actual cause.

    So...It would have been helpful to know the distributor nozzle size.

    In the meantime, I tend to lean toward simply going up one size on the TXV from what's called for. Unless you have a system with floating head pressure or unloading, I doubt you'll ever have a TXV control problem from its being oversized.

  5. #57
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    Nov 2006
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    Quote Originally Posted by ar_hvac_man View Post
    Changed powerhead, no change. Put in the number 4 and shes rockin and rollin

    Thanks guys!
    Great news!!!
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  6. #58
    Join Date
    Jun 2012
    Location
    Afghanistan
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    16
    Is the box sealed? Are there any air gaps on the door?

  7. #59
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    Mar 2007
    Location
    NW AR
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    Me again Margaret....

    Had a free minute to go check how the freezer is doing. Everything checks out good except my pressure and coil temp. SH 8deg at the bulb. Pressure 15 psi....-20 degree coil. Box hovers at 0 and wont get colder obviously because my suction is too high. My SC is also low at 3 deg but I have a clear sight glass?

    Good SH but I want lower suction so the box will pull down. To get lower suction pressure Id have to squeeze down the TXV which will raise my SH and my evap wont be flooded.

    The distributor nozzle subject keeps scratching at my brain. Can someone explain how going to a bigger nozzle would help?

  8. #60
    Join Date
    Sep 2005
    Location
    florida
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    5,514
    Quote Originally Posted by ar_hvac_man View Post
    Me again Margaret....

    Had a free minute to go check how the freezer is doing. Everything checks out good except my pressure and coil temp. SH 8deg at the bulb. Pressure 15 psi....-20 degree coil. Box hovers at 0 and wont get colder obviously because my suction is too high. My SC is also low at 3 deg but I have a clear sight glass?

    Good SH but I want lower suction so the box will pull down. To get lower suction pressure Id have to squeeze down the TXV which will raise my SH and my evap wont be flooded.

    The distributor nozzle subject keeps scratching at my brain. Can someone explain how going to a bigger nozzle would help?



    First do you know if the right nozzle was installed???
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  9. #61
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    Mar 2007
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    NW AR
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    I installed the low temp 404A nozzle that came with the evap

  10. #62
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    Mar 2007
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    NW AR
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    Granted, it could have been the wrong one in the bag i guess. Ive only installed around 12 complete new cooler or freezer systems. This is the first Ive had any problem with. Ill know in the future to verify correct nozzle sizing. How would a bigger nozzle help is what im asking.

  11. #63
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    NW AR
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  12. #64
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    Jul 2000
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    Guayaquil EC
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    Quote Originally Posted by ar_hvac_man View Post
    Me again Margaret....

    Had a free minute to go check how the freezer is doing. Everything checks out good except my pressure and coil temp. SH 8deg at the bulb. Pressure 15 psi....-20 degree coil. Box hovers at 0 and wont get colder obviously because my suction is too high. My SC is also low at 3 deg but I have a clear sight glass?

    Good SH but I want lower suction so the box will pull down. To get lower suction pressure Id have to squeeze down the TXV which will raise my SH and my evap wont be flooded.

    The distributor nozzle subject keeps scratching at my brain. Can someone explain how going to a bigger nozzle would help?
    The superheat could still stand to be bit lower to around 4-6F. You'd be amazed at how much difference it can make. But be sure you're measuring the suction pressure at the coil and not at the compressor when you figure the SH because that couple of pounds of pressure drop in the suction line will throw you way off in a hurry at these temperatures.

    Your subcooling usually won't get much higher than what you've got simply because it's got a receiver in the system. There's no adjusting that with charge...or anything else. And yes, by definition at 3F SC you'll have a clear glass.

    Get it out of your head about altering the suction pressure by messing around with the expansion valve. It's not a pressure regulator...it's a superheat regulator.

    As for the nozzle question, we've already made a fix of sorts by upsizing the TXV capacity. This did one of two things. Either the nozzle was actually OK sizewise and the TXV was undersized...or the other way 'round. So at this point, unless you find you can't get the SH down to where you need it, I wouldn't be concerned about the nozzle sizing. The superheat is a major factor in telling you whether the coil is performing or not.

    The one thing which stands out here is the relatively high TD on the evaporator. You say the box is at 0F and the coil is at -20F SST, which gives a 20F TD. At design conditions it should be a 10F...but what are the design conditions for this job?

    By the numbers we have, the coil has a specific capacity of 9400 Btuh at a 10F TD and the condensing unit has a capacity of about 9400 Btuh at -20F SST and 90F ambient, so I'm assuming the system was selected for a -10F box temperature...correct?

    I think a lower superheat will help lower the TD and subsequently raise the suction pressure & lower the box temperature...but another 10F lower may be a push. Of course there may be other factors in play here.

  13. #65
    Join Date
    Jul 2012
    Location
    Western KY
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    Quote Originally Posted by crackertech View Post
    Just a thought I once had coil we ordered fore R-22 but it was shipped with a 404 orifice in it drove us crazy.
    That's what I was thinking too. But should see some movement with the adjustment. Wouldn't waste alot of time here. Pull it, verify orifice, and replace valve. Assuming you are confident the charge is correct.

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