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  1. #1
    Join Date
    Mar 2013
    Location
    Maine
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    477

    head pressure regulating valves

    question: on a system with head pressure regulating valves for low ambient conditions, will they still maintain close to proper head pressure even with a low charge? Or is this going to be true to a certain extent but if the systems charge is low enough it will eventually start to bring head pressure down to an abnormal level?
    trying to understand these better. thanks in advance

  2. #2
    Join Date
    Mar 2011
    Location
    Galloway, Ohio
    Posts
    62
    The lower the outside ambient the more refrigerant the system needs to flood the condenser. So typically if the unit is low it will show during colder temps, the rest of the time it fills the receiver with refrigerant so often tiumes you won,t have low reefer symtoms during warmer outdoor weather. Sporlan has a very good bulletin on this 90_ 30 think.

  3. #3
    Join Date
    Mar 2011
    Location
    North Carolina Piedmont Area
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    449
    What is the application?
    What is the tonnage?
    What type of metering device do you have?
    What type of compressor are you using?
    Multiple circuits?
    What are the design conditions?
    What type of refrigerant?
    What specific head pressure device are you using?
    But I am still learning and looking for a new mentor.
    _______________________
    In a strict sense troubleshooting is not part of the repair..........understand the symptoms and you will find a solution.

  4. #4
    Join Date
    Mar 2013
    Location
    Maine
    Posts
    477
    Quote Originally Posted by palmeri View Post
    The lower the outside ambient the more refrigerant the system needs to flood the condenser. So typically if the unit is low it will show during colder temps, the rest of the time it fills the receiver with refrigerant so often tiumes you won,t have low reefer symtoms during warmer outdoor weather. Sporlan has a very good bulletin on this 90_ 30 think.
    Thats what I was thinking because Ive been reading those sporlan bulletins haha, I just found them last week and saved them, thanks for the clarification

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567
    Quote Originally Posted by palmeri View Post
    The lower the outside ambient the more refrigerant the system needs to flood the condenser. So typically if the unit is low it will show during colder temps, the rest of the time it fills the receiver with refrigerant so often tiumes you won,t have low reefer symtoms during warmer outdoor weather. Sporlan has a very good bulletin on this 90_ 30 think.

    http://sporlanonline.com/literature-...lating-valves/

    90-30-1 has the charging guidelines for units with these valves installed.


    The head pressure valves will attempt to maintain their set pressure until the refrigerant charge is too low to do so.

  6. #6
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    895
    Plmeri stated it in a nutshell and provided the sporan bulletin. I just wanted to add that in severe cases you can actually hear the hot gas flowing though the lac valve and the liquid line will be hot. The constant loud hiss has been the immediate tip off for me. This usually happens during the first cold snap and the equipment was charged in warm weather not paying attention to the lac valve.
    ckartson
    I didn't write the book I just read it!

  7. #7
    Join Date
    Mar 2011
    Location
    Galloway, Ohio
    Posts
    62
    Sporlan's website is a wealth of info. I would also suggest using the search option on this site for accessing some of the archives on this subject, there are some great ones.

  8. #8
    Join Date
    Apr 2010
    Location
    California
    Posts
    38
    Is this it, a commercial for sporlians web site?

  9. #9
    Join Date
    May 2003
    Location
    Utah
    Posts
    721
    Common mis-diagnosis is to see a system short on charge (either from a leak, or from never being charged correctly in the first place), with a receiver that is hot (from the bypassed discharge gas) and empty..and the valve is condemned as defective.

    Of course this symptom is caused by the under charge, and the valve is just doing what it is supposed to do: maintain a minimum head pressure by flooding the condenser with liquid refrigerant, reducing the effective condenser size and raising head pressure. With no liquid refrigerant left to maintain a liquid seal in the receiver the valve bypasses discharge gas continuously, resulting in the hot receiver.

    The alleged defective valve is replaced, the system is evacuated and then charged to a full sight glass, the system operates properly...all "confirming" that the original valve had failed.

    And the tech feels good about solving the problem and moves on to the next job, none the wiser.

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