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  1. #53
    Join Date
    Jan 2004
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    Lancaster PA
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    Quote Originally Posted by garyed View Post
    I 100% agree, we seem to have an argument about once a year about whether a liquid line restriction can cause elevated head pressure without the system being over charged. They obviously don't teach that in class so only those who have experienced it in the field can attest to it.

    RTU and a split system are different, hen it comes to having a high head with a restricted LLFD. Microchannel condensers will have a high head as they just don't hold much volume, so there is no room for all the liquid refrigerant to stack up in them.
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  2. #54
    Join Date
    Jul 2009
    Location
    South Carolina
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    3,063
    Quote Originally Posted by beenthere View Post
    RTU and a split system are different, hen it comes to having a high head with a restricted LLFD. Microchannel condensers will have a high head as they just don't hold much volume, so there is no room for all the liquid refrigerant to stack up in them.
    From what I've seen the microchannel units act no different than any tube & fin unit. They just hold less gas which makes them more sensitive to charge & they leak a lot. They probably hold the same amount of gas as an older 8 or 10 SEER might. I don't see how that would make that much of a difference. I've pumped down plenty of microchannel units before I ever knew I wasn't supposed to & they pumped down just fine. On long line sets I had to remove some gas first no different than I would any other type of unit. I'm not arguing that they can hold as much gas in the condenser as a regular unit but just that there was already less gas to compensate for in the system if the charge was correct so I don't see how that changes the basic principles.
    Gary
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    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  3. #55
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,704
    Quote Originally Posted by garyed View Post
    From what I've seen the microchannel units act no different than any tube & fin unit. They just hold less gas which makes them more sensitive to charge & they leak a lot. They probably hold the same amount of gas as an older 8 or 10 SEER might. I don't see how that would make that much of a difference. I've pumped down plenty of microchannel units before I ever knew I wasn't supposed to & they pumped down just fine. On long line sets I had to remove some gas first no different than I would any other type of unit. I'm not arguing that they can hold as much gas in the condenser as a regular unit but just that there was already less gas to compensate for in the system if the charge was correct so I don't see how that changes the basic principles.
    Old 8 and 10 SEER condensers could hold a lot og refrigerant. Micro channels can't hold nearly as much. Try pumping one down to itself.
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  4. #56
    Join Date
    Jul 2009
    Location
    South Carolina
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    Quote Originally Posted by beenthere View Post
    Old 8 and 10 SEER condensers could hold a lot og refrigerant. Micro channels can't hold nearly as much. Try pumping one down to itself.
    I don't want to hijack this thread so I'll give up until this comes up in another thread.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  5. #57
    Join Date
    Feb 2010
    Location
    IL
    Posts
    123
    Quote Originally Posted by gravity View Post
    i have a video of a drier i just found restricted. a carrier 28ton rtu. circuit #1 had pressures of 40/600. 600psi before the drier and 250 after the drier. this was a new microchannel coil. no temp split across drier but a pressure drop of 350psi! if i wouldnt have been able to check across that drier i would have said the condenser was restricted.
    Wait? A pressure drop across the filter dryer didnt cause a temp drop? How is that possible? P/T relationship? Being that there is no load on that causing it to gain or lose heat just pressure drop should of cause temp difference? I had one last week that had a 50 degree drop across it, frosted on one side... Must be a rare one then.. Like to know on that, been a service guy for 2-3 years or so now residential and commercial RTU. Please enlighten me. Not saying your wrong at all, just want to learn more! LEARN EVERYDAY!

  6. #58
    Join Date
    Jul 2009
    Location
    Columbia, MD
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    3,787
    there is a thread floating around here somewhere describing why you wont always have a temp split.

  7. #59
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
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    Hvacrmedic is the guy who wrote what gravity mentioned.

    Another trick is that when the unit has been overcharged the increased sc tends to help mask restrictions.

    So the trick is kill the indoor fan and possibly recover some of charge and that will cause SC to drop which will cause more of a temp drop across suspect part.

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