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  1. #1
    Join Date
    Oct 2010
    Location
    oregon
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    46

    Sub Cooling & Superheat question

    Gentleman,

    Ive been learning up on SH & SC and it seems there are a 100 different answers and opinions on it. But that seems to be the norm about everything.

    Question is why does a A/C or H/P use SC on TXV systems and SH on orfices/pistons? And then why does a Refrigeration unit if it has a valve require SH method? Does elp SC method work on heat pumps in heating mode?

    Thanks for your help guys

  2. #2
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by Rmarshall View Post
    Gentleman,

    Ive been learning up on SH & SC and it seems there are a 100 different answers and opinions on it. But that seems to be the norm about everything.

    Question is why does a A/C or H/P use SC on TXV systems and SH on orfices/pistons? And then why does a Refrigeration unit if it has a valve require SH method? Does elp SC method work on heat pumps in heating mode?

    Thanks for your help guys
    Good questions there

    Why have you not? or have you applied for "Pro" yet?

    Better answers and details on the other side of the fence, just sayin

  3. #3
    Join Date
    Jul 2011
    Location
    Vancouver BC Canada
    Posts
    30
    Quote Originally Posted by Rmarshall View Post
    Gentleman,

    Ive been learning up on SH & SC and it seems there are a 100 different answers and opinions on it. But that seems to be the norm about everything.

    Question is why does a A/C or H/P use SC on TXV systems and SH on orfices/pistons? And then why does a Refrigeration unit if it has a valve require SH method? Does elp SC method work on heat pumps in heating mode?

    Thanks for your help guys
    99.9% on high seer heat pumps and a/c units use a txv that is not adjustable. So the only way to properly charge the system is sub cooling in the cooling mode. Taking the wet bulb return air temp and the ambient temp, look at the charge table to see how much refrigerant you need.
    As far as refrigeration system 99.9% of these units use a adjustable txv because the load changes so much with door opening warm stock etc...Also because of pump down, defrost etc..

    just my opinion

  4. #4
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by Heritage MT View Post
    99.9% on high seer heat pumps and a/c units use a txv that is not adjustable. So the only way to properly charge the system is sub cooling in the cooling mode. Taking the wet bulb return air temp and the ambient temp, look at the charge table to see how much refrigerant you need.
    As far as refrigeration system 99.9% of these units use a adjustable txv because the load changes so much with door opening warm stock etc...Also because of pump down, defrost etc..

    just my opinion
    Hmmm, so "if" I happen to check it anyway, unlike you and found it to be 50+ SH, with Okay SC, I should just ignore it then??

  5. #5
    Join Date
    Jun 2011
    Location
    Hammond,La.
    Posts
    1,176
    The short answer,
    Systems with TXV's use sub cooling because the TXV tries to keep a constant designed SH.
    You charge fixed, orifice systems by Sh to make sure the liquid line is full of liquid and not boiling off before the orifice.

    Both measurements are very important to a systems health and diagnosis but this is the basics of it.

  6. #6
    Join Date
    Jul 2011
    Location
    Vancouver BC Canada
    Posts
    30
    Quote Originally Posted by Chris_Worthington View Post
    Hmmm, so "if" I happen to check it anyway, unlike you and found it to be 50+ SH, with Okay SC, I should just ignore it then??
    I am not sure I understand what you mean. I could not imagine not checking both s/c and s/h to see what is going on.
    If that was the case with the s/h 50+ and s/c around normal which I can not see how that could be but for argument sake lets just say it is I would be looking for a leak if the system has been running ok for a while. If its a new split system it could be just under charged.

  7. #7
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by Heritage MT View Post
    I am not sure I understand what you mean. I could not imagine not checking both s/c and s/h to see what is going on.
    If that was the case with the s/h 50+ and s/c around normal which I can not see how that could be but for argument sake lets just say it is I would be looking for a leak if the system has been running ok for a while. If its a new split system it could be just under charged.
    Okay SC and high SH is under charged?

    Curious with a clamp on temp probe how long does it take anyways for this extra service?

  8. #8
    Join Date
    Jul 2011
    Location
    Vancouver BC Canada
    Posts
    30
    Quote Originally Posted by Chris_Worthington View Post
    Okay SC and high SH is under charged?

    Curious with a clamp on temp probe how long does it take anyways for this extra service?
    I use a yellow jacket refrigeration analyzer for all my refrigeration work. It only takes seconds to put it on. All units we install comes with a 10 year parts and labor warranty and with these gauges I record a proper vacuum and run operation. I cant afford call backs so we do our best to prevent them. I also do warranty work for York so I send them PDF files on the systems as to what we find.

    Low sub cool and high super heat yes can be undercharged, dirty coil, dirty filter... evaporator is not picking up any heat.

  9. #9
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
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    7,281
    Quote Originally Posted by Heritage MT View Post
    I use a yellow jacket refrigeration analyzer for all my refrigeration work. It only takes seconds to put it on. All units we install comes with a 10 year parts and labor warranty and with these gauges I record a proper vacuum and run operation. I cant afford call backs so we do our best to prevent them. I also do warranty work for York so I send them PDF files on the systems as to what we find.
    Hmmm, get you're post count up there and we will see you on the other side of the fence and have a happy 4th

  10. #10
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281

  11. #11
    Join Date
    May 2007
    Location
    Michigan
    Posts
    324

    Hello

    Heya
    I would think to check both.
    The problem I typically see is that "normal" people know of only one superheat and one subcooling location. I am not sure but I think there are a couple of "locations" , example - compressor superheat, evaporator superheat, condenser subcooling, epansion device subcooling/superheat.
    I just know most people take the superheat method becouse it easy to remember, and most P-h chart refrig/temp conversion cards show "Superheat Method". But if you really want to stay safe you also take the subcooling of your condensation circuit.

  12. #12
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by durussel78 View Post
    Heya
    I would think to check both.
    The problem I typically see is that "normal" people know of only one superheat and one subcooling location. I am not sure but I think there are a couple of "locations" , example - compressor superheat, evaporator superheat, condenser subcooling, epansion device subcooling/superheat.
    I just know most people take the superheat method becouse it easy to remember, and most P-h chart refrig/temp conversion cards show "Superheat Method". But if you really want to stay safe you also take the subcooling of your condensation circuit.
    Curious when you're playing it "safe" does this take up a bunch of time on you're behalf? and have you "or" do you play it "safe" when the shoe is on the SH side of things?

    Really this should be in Pro BTW and can only let this thread continue here in the open areas of the site for so long, sooooo

  13. #13
    Join Date
    Jul 2011
    Location
    Vancouver BC Canada
    Posts
    30
    Quote Originally Posted by Chris_Worthington View Post
    Hmmm, get you're post count up there and we will see you on the other side of the fence and have a happy 4th
    Yes u too

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