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refrigerent traps and subcooling

what is the function of an inverted suction trap on a system where the condenser is above the evap. And in a refrigeration system with a txv/receiver where does one measure subcooling. Thanks, Michael.


  • TonySTonyS Member Posts: 849
    edited October 2013
    The trap

    is there to insure oil returning to the compressor.

    I check my subcooling right after the condenser.
  • charliechicagocharliechicago Member Posts: 68
    whats the difference

    in function of a regular trap vs an inverted strap. Thanks Mike
  • charliechicagocharliechicago Member Posts: 68
    i meant

    trap not strap
  • pecmsgpecmsg Member Posts: 170

    1st All piping needs to be done to manufactures specs. There is a large differance between A/C and Refrigeration

    When the condensing unit in a Refrigeration System is higer then the evaporator a P-Trap is installed at the low point to aid in oil return.

    A Inverted P-Trap is used to prevent liquid refrigerant from running down to a compressor.

    Sub Cooling cannot be used with a receiver.
  • TechmanTechman Member Posts: 2,144

    Refrigeration systems w/ recievers use SubCooling ,just like AC. The receiver itself is different as far as SC is concerned
  • pecmsgpecmsg Member Posts: 170
    S C

    S C is telling you how much refrigerant is or isn't backing up in the condenser. On A/C systems it is a valuable tool for measuring if you are getting a full column of liquid to the metering device.


    Once a receiver is installed you can have liquid, vapor, or both leaving the condenser but the liquid seal in the receiver guaranties a full column of liquid to the metering device. The SC reading will hardly change no matter how much refrigerant you add or remove as long as you don’t overfill the receiver or loose the liquid seal.
  • TechmanTechman Member Posts: 2,144
    edited October 2013

    I'm pretty sure that the liquid line in between the outlet of the cond coil and the inlet of the reciever is filled w/ liquid only. And w/ the cond unit above the evap you need only a couple of * of SC. W/ cond below evap the SC required changes in relation to vertical separation, just like AC. I think.
  • charliechicagocharliechicago Member Posts: 68

    for the responses. pecmsg, but where do you take the actually the subcooling measurement. Also, you talk about a liquid seal. I understand that to mean, no matter where the outlet to the receiver is, you always have liquid leaving . If the outlet is on the bottom there is liquid there and if its on the top you have a dip tube into the liquid. So on a slightly undercharged  system you should have enough liquid to maintain a liquid seal, why do you get bubbles in the sight glass?  Thanks, Mike.
  • TechmanTechman Member Posts: 2,144
    edited November 2013
    recievers/ SC

    What Freon? On a properly charged system the SightGlass should be full under all normal operating conditions. Bubbling in the SG is normal for some freons. Bubbles-like in gingerale- does (11-3-13 correction)   not mean the system is undercharged. Activity in the SG or a "level" of liquid/vapor in the SG does indicate a system low on Freon. TXV's on AC/R operate identically( SuperHeat is a couple of * different), they both need a "full liquid line" at the TXV under all normal operating conditions. So a r-22 AC and a r-22 ref system operate the same, as far as SC , if the vertical separation is the same. There are a few more factors involved w/ refrigeration. AC SEER does play a little differently, but not much.
  • VA_BearVA_Bear Member Posts: 50
    edited October 2013
    Not quite...

    The inverted trap is at the top of the suction riser when the condenser is above the evaporator and the standard trap(s) are at the bottom of the suction riser and may be in the intermediate suction riser if it is tall enough to need the extra help. The inverted trap has nothing to do with liquid refrigerant (if you have liquid in a suction line, you have a MAJOR problem).

    The bottom trap partially fills with oil coming from the evaporator coil and draining back from the suction riser, where the suction gas picks it up in large drops from the pool in the trap and transports them up to the roof and over the top of the inverted trap, which prevents the oil from draining back down the suction riser.

    You are right that subcooling cannot be used to set the charge in a receiver equipped system because the subcooling is substantially the same for all the liquid from the point that the liquid line is just filled to the point that the receiver is almost completely full.
  • TechmanTechman Member Posts: 2,144
    edited October 2013

    Morning! Hi VA Bear. An AC cond unit  is side by side w/ a refrig cond unit ( w/ receiver ) , both r22 , both 3/8 liquid line , both LL go up 25', both LL then go 25' horizontal, into their evaps, both TXV. The required SC for the TXV is different?
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