Results 1 to 11 of 11

Thread: Frost

  1. #1
    Join Date
    Jan 2013
    Location
    Australia
    Posts
    35
    Rep Power
    0

    Frost



    Hi everyone,

    has anyone come across a instance where you have normal to more than normal evaporator superheat but have liquid returning to the comp in the suction line ??

    Many thanks



  2. #2
    Join Date
    Feb 2007
    Location
    UK
    Posts
    2,479
    Rep Power
    45

    Re: Frost

    Well, by definition that situation would not be possible on a correctly designed system.

    Superheat = temperature of the refrigerant above the temperature at which the refrigerant evaporated.

    Now, the only reason for liquid to be carried over even when the superheat is there would be if the velocity of the refrigerant is too high in the suction line (for example if the suction line is to short or too narrow).



    .

  3. #3
    Join Date
    Aug 2006
    Location
    england
    Age
    49
    Posts
    3,874
    Rep Power
    46

    Re: Frost

    Wrong refrigerant in system, poorly designed pipework, had system with air in that would slug liquid back now and again once.
    Mostly found in Oxfordshire, UK :)

  4. #4
    Join Date
    Jan 2013
    Location
    Australia
    Posts
    35
    Rep Power
    0

    Re: Frost

    Quote Originally Posted by The Viking View Post
    Well, by definition that situation would not be possible on a correctly designed system.

    Superheat = temperature of the refrigerant above the temperature at which the refrigerant evaporated.

    Now, the only reason for liquid to be carried over even when the superheat is there would be if the velocity of the refrigerant is too high in the suction line (for example if the suction line is to short or too narrow).



    .
    I must say i agree with your definition, this system seems to be defying logic.

    It is a old R12 system running on R134a. It has tube and fin condenser and evaporator. The evaporator is face split, divided into 2 sections. Liquid flows to single txv and then the line is divided to feed the upper and lower sections of the evaporator.

    I do suspect uneven distribution to the evaporator sections as the lower section has frost on every tube and the upper section has frost only on the lowest tubes, the upper tubes only show a little condensation.

    Suction pressure is 15psig, and suction temp is 5 degrees C. Superheat= 14.4 degrees C, but there is frost on the compressor suction line fitting, it is at -2 degrees C.

    Temp is dropping 7 degrees C over the length of the suction line. Which makes me think there must be liquid in it evaporating, but with 14.4 degrees superheat that seems not possible ???

    The suction line is short, only 20 inches. It's diameter is 3/4 inch, which seems to be the standard suction line size for these compressors. System design is definately out of whack with R134a in a R12 system.

    Any more thoughts anyone ??

  5. #5
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
    Join Date
    Mar 2001
    Location
    Dorset
    Age
    76
    Posts
    11,192
    Rep Power
    60

    Re: Frost

    Seems that the lower section of the coil has liquid flowing through it and vapour going through the upper section.

    Are the two tubes from the TXV shaped in any way to encourage equal flow in the tubes or are they simple straight runs into the coil?

    Also, is the sensing bulb of the TXV in a good location?

    A second also, is the TXV externally equalised?
    [edit]
    This is something that Sporlan pick up on in their literature, see The Distribution Problem on page 2 of this...
    http://www.sporlanonline.com/20-10_022011.pdf
    Last edited by Brian_UK; 29-01-2013 at 12:03 AM. Reason: Added a bit more.
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

  6. #6
    Join Date
    Aug 2006
    Location
    england
    Age
    49
    Posts
    3,874
    Rep Power
    46

    Re: Frost

    As Brian said, have seen tev outlet split in two where liquid ran through lower tube and vapour in the other, this resulted in low duty, flooding back and in this case lower half of coil frosted over.

    Turned the distributor through 90' so both tubes where horizontal and sid by side.
    Mostly found in Oxfordshire, UK :)

  7. #7
    Join Date
    Jan 2013
    Location
    Australia
    Posts
    35
    Rep Power
    0

    Re: Frost

    Quote Originally Posted by Brian_UK View Post
    Seems that the lower section of the coil has liquid flowing through it and vapour going through the upper section.

    Are the two tubes from the TXV shaped in any way to encourage equal flow in the tubes or are they simple straight runs into the coil?

    Also, is the sensing bulb of the TXV in a good location?

    A second also, is the TXV externally equalised?
    [edit]
    This is something that Sporlan pick up on in their literature, see The Distribution Problem on page 2 of this...
    http://www.sporlanonline.com/20-10_022011.pdf
    I feel the distributor tubes do not really encourage equal flow. I'll post a picture.

    The txv is externally equalized and i think the bulb location on the suction line just downstream from the evaporator is pretty good.

    ac 5 003s.jpg

  8. #8
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
    Join Date
    Mar 2001
    Location
    Dorset
    Age
    76
    Posts
    11,192
    Rep Power
    60

    Re: Frost

    Yep, looks like you need to rotate that distributor by 90°.

    For a video of the effects in a similar scenario, Daikin Refnet, see here....
    http://www.youtube.com/watch?v=HcyfweCquR0
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

  9. #9
    Join Date
    Jan 2013
    Location
    Australia
    Posts
    35
    Rep Power
    0

    Re: Frost

    Yes, rotating by 90 is great idea and i definately like to try it, but unfortunately it is not possible to get to it as it is buried deep inside a car's dashboard (the photo is of a spare) and i'm not keen on dismembering the car.

    I redirected the evaporator fan's airflow to force more air over the lower section, this helped, but given that reorienting the distributor is not so easy to do i wonder if there might be other solutions ??

  10. #10
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    60
    Posts
    1,492
    Rep Power
    24

    Re: Frost

    Quote Originally Posted by Brian_UK View Post
    Yep, looks like you need to rotate that distributor by 90°.

    For a video of the effects in a similar scenario, Daikin Refnet, see here....
    http://www.youtube.com/watch?v=HcyfweCquR0
    That picture is worth a thousand words

  11. #11
    Join Date
    Jan 2013
    Location
    Australia
    Posts
    35
    Rep Power
    0

    Re: Frost

    Quote Originally Posted by MikeHolm View Post
    That picture is worth a thousand words
    Yes, a excellent video.

    It really makes me wonder how these things can be manufactured with such obvious defects ?

    Surely it costs nothing to orient parts in the correct way ?

    A big thankyou for every ones help *

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •