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  1. #1
    Join Date
    May 2007
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    DC Metro Area (MD)
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    3,369

    Trying to learn: pressures/refrigerant direction

    I'm trying to learn more about the refrigerant cycle--just out of curiosity and interest.

    For quite a while I had the cooling refrigerant cycle backwards--I thought the suction line, since it was insulated, was bringing the refrigerant to the coil. I now realize it is the smaller liquid line. In heating mode, I was told this reverses.

    What I am trying to know--just out of curiosity--is which side is the "high side" (high pressure) and "low side" (low pressure) during each mode. I've been to a number of websites and can't seem to figure it out, so I figured I'd take a more direct approach and ask the pros right here.

    Anyone care to share some knowledge? I'd appreciate it--thanks.

  2. #2
    Join Date
    Jul 2007
    Location
    SA
    Posts
    127
    This Will ansewer all your ?


    Basic Refrigeration & Charging Procedures Interactive CD-rom

    http://www.licensedelectrician.com/Store/ES/RCP.htm

  3. #3
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    3,369
    Thank you. That looks really good, but I don't need to charge any systems. I'm just asking so I'm more familiar with the refrigerant cycle (out of interest/curiousity). Anyone care to answer my simple question regarding the "pressure sides" during heating and cooling mode for heat pumps? Thanks.

  4. #4
    liquid line is highside during heating and cooling, flow of refrigerant just changes directions.suction line becomes discharge line in heating mode.during cooling inside coil is evaporator outside coil is condenser they swap jobs during heating mode.hard to understand until you know how metering device,reversing valve etc. operates.hope this helps

  5. #5
    Join Date
    May 2007
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    DC Metro Area (MD)
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    Quote Originally Posted by mississippi View Post
    liquid line is highside during heating and cooling, flow of refrigerant just changes directions.suction line becomes discharge line in heating mode.during cooling inside coil is evaporator outside coil is condenser they swap jobs during heating mode.hard to understand until you know how metering device,reversing valve etc. operates.hope this helps
    Thank you mississippi. I appreciate you kindly sharing this info. Just wanted to know this about the refrigerant cycle.

  6. #6
    Join Date
    Apr 2002
    Location
    Omaha, NE
    Posts
    1,561
    Ryan,
    Here's a good review of the heat pump cycle in cooling & heat modes with graphics: http://www.refrigerationbasics.com/1...eat_pumps1.htm

  7. #7
    Join Date
    Jun 2007
    Location
    Central, FL
    Posts
    871
    Ryan do you even understand how a A/C cools or heats? If not you need know learn this first before anything else you want me to explian? makes it easier to understand
    WARNING:IF YOU DON'T KNOW THEN DON'T DO, SO THOSE WHO KNOW WHAT YOU DIDN'T KNOW DON'T END UP UNDOING WHAT YOU DID SO IT COULD GET DONE RIGHT!

  8. #8
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,369
    Thank you. ACDoc, I think I understand all I need to/would like to know about how heat pumps/air conditioners work. In my attempt to find an answer to my original question, I came accross from nice Web sites that explained how they work.

    Am I right to assume that "head pressure" means discharge side pressure (high side)?

  9. #9
    Join Date
    Jul 2007
    Location
    SA
    Posts
    127
    yes

  10. #10
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    3,369
    Quote Originally Posted by mississippi View Post
    liquid line is highside during heating and cooling, flow of refrigerant just changes directions.suction line becomes discharge line in heating mode.during cooling inside coil is evaporator outside coil is condenser they swap jobs during heating mode.hard to understand until you know how metering device,reversing valve etc. operates.hope this helps
    I just came across this posting somewhere else in the forums which says the bigger line is the high pressure line in heating mode (whereas the smaller line is the high pressure line in cooling mode):

    "This is a high pressure line in the heat mode. In a heat pump it is not a suction line but a vapor line. The only part of the system that is a suction line is at the outlet of the reversing valve to the compressor. Just terms used to describe the system. Just as the evaporator is an indoor coil, and the condenser is the outdoor coil."

    Now I'm not sure what's right. Would anyone mind clarifying on my behalf? Thanks.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,778
    The large line, becomes the hot gas discharge line in heating mode.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #12
    Join Date
    Apr 2007
    Posts
    6,285
    Here is a heat pump cycle with TXV's and check valves.
    Attached Images Attached Images   

  13. #13
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    3,369
    Thanks to you both--I appreciate the knowledge you kindly share. Nice diagrams, Jon. Discharge I take as meaning high pressure because that comes right from the compressor, correct? Just interested in knowing which line is the high pressure and which one is the low pressure during both modes. Right now I understand it as:

    Heating Mode:
    Large line - high pressure, discharge gas
    Small line - low pressure, returning liquid

    Cooling mode:
    Large line - low pressure, returning gas (suction)
    Small line - high pressure, saturated vapor (barely liquid), discharge

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