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  1. #14
    Join Date
    Sep 2008
    Location
    Cedar Rapids, IA
    Posts
    486
    Quote Originally Posted by Chris_Worthingt View Post
    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
    It is not a good idea to bypass a low pressure control w a timer for pump down purposes. A timer to bypass a low pressure control on startup in cold weather is common, but the question here seems to be about prolonging pump down. Scroll compressors can be damaged by pumping down too low. If the timer ever failed this could happen. It would be a better idea to put a 2nd low pressure switch in. (or widen the cut in cut out differential spread on the existing control)

  2. #15
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Quote Originally Posted by bob_scheel View Post
    It is not a good idea to bypass a low pressure control w a timer for pump down purposes. A timer to bypass a low pressure control on startup in cold weather is common, but the question here seems to be about prolonging pump down. Scroll compressors can be damaged by pumping down too low. If the timer ever failed this could happen. It would be a better idea to put a 2nd low pressure switch in. (or widen the cut in cut out differential spread on the existing control)
    Its done everyday in the refer world among others, never ever caused an issue and is generally a required part of the sequence of operations, timing out a safety in a lot of circumstances is a requirement, period

  3. #16
    Join Date
    Sep 2002
    Location
    Hampton Roads, Virginia
    Posts
    1,627
    Johnson make a low pressure switch with built in time delay the P29 series.
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    "There are 10 types of people in the world.. those who understand binary, and those who don't."

  4. #17
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,724
    Can you name a few refrigeration systems that use scroll compressors for pumpdown? I need to know for reference. I wonder how low pressure they really go.
    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.

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