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  1. #1
    Join Date
    Nov 2008
    Posts
    4

    LP switch time delay

    Help me- I can't figure out how to draw a time delay into a simple safety circuit. High pressure, Low pressure switches. I need the unit to continue running after the low pressure switch opens for a couple seconds. I just can't figure out how to draw it.

  2. #2
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,140
    *************** TDR
    ******* |----------O------------------ Neutral
    ******* |*****|--|/|--|
    **Line ---|--HP--|--LP--|--- LOAD

    I would just draw something like this.
    Last edited by dapper; 11-05-2008 at 09:44 PM. Reason: Didn't read the criteria right at first

  3. #3
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,700
    Why would you want to keep a compressor running after the low pressure switch opens? What does 3 seconds matter?
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  4. #4
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,140
    This type of time delay (delay-on-break) is generally used to bypass the low pressure switch on compressor start-up when there might be a cold evap or condenser. Not sure why it would run after the LP opens otherwise.

  5. #5
    Join Date
    Nov 2008
    Location
    Auckland New Zealand
    Posts
    56
    I would rather find the solution to why the LP is dropping that low on start up in the first place the delay on break relay is mearly a Band-Aid solution check the super heat and LP cut out settings.

  6. #6
    Join Date
    Dec 2005
    Location
    San Jose, CA
    Posts
    465
    Maybe this is apprenticeship homework!!

  7. #7
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,140
    Not a Band-Aid solution at all. A very common and necessary solution often provided from the factory for those of us in much colder climates than you guys.

  8. #8
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by dapper View Post
    Not a Band-Aid solution at all. A very common and necessary solution often provided from the factory for those of us in much colder climates than you guys.
    I thought it was common practice regardless of location, as in any pump-down system

  9. #9
    Join Date
    Mar 2003
    Location
    NY
    Posts
    2,140
    Real common in pump-downs but I'm also thinking about heat pumps and water source heat pumps without pump-down.

  10. #10
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by dapper View Post
    Real common in pump-downs but I'm also thinking about heat pumps and water source heat pumps without pump-down.
    Agreed there are many app's where this needed and used often

    Was trying to address thegoodlistener and kiwicontroller comments, as in this is common practice and has nothing to do with a band-aid approach

  11. #11
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,700
    Quote Originally Posted by Chris_Worthingt View Post
    Agreed there are many app's where this needed and used often

    Was trying to address thegoodlistener and kiwicontroller comments, as in this is common practice and has nothing to do with a band-aid approach
    The OP doesn`t say whether he is trying to bypass at start-up. So my assumption was why trying to bypass at safety on a normal safety trip out.
    I know most manufacturers have an approved low ambient start kit for this purpose and more safisticated controls should have this built in.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  12. #12
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Who said anything about start-up?

    I thought a normal situation where this this would be used i.e. Pump down would occur at the end of a cycle

    There are many app's where timing out a safety is called for, the facts, not a band-aid

  13. #13
    Join Date
    Jan 2005
    Location
    Area 51
    Posts
    984
    "Paddle faster, I hear banjo music"

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