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  1. #1
    Join Date
    Mar 2002
    Posts
    79

    Heat pump not completely thawing

    Hi Guys: I have a ICP heat pump that is working ok. but it doesn't defrost the coils completely. The defost cycles are set for every 30 mins. I am getting a band of heavy frost staying around the middle on the outside coil. I have seen this before on other units. is this normal do to heavy work load when the weather is cooler, and the unit doesn't get a break?
    When it goes on defrost. the bottom coil is getting cleaned up , where the defrost termination sensor is.
    Adonis

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,418
    I'd suspect low refrigerant charge.

  3. #3
    Join Date
    May 2006
    Posts
    65
    i've run into the same problem, and you know what caused it was a low refrigerant charge, i'm a 4th year apprentice and 2 journeymen that have over 8 years experience couldn't figure it out so the boss sent the apprentice and I figured out what it was, weigh the charge out and i'm almost positive you you'll find the charge low...

  4. #4
    Join Date
    Jun 2006
    Posts
    147
    DITTO low chg

  5. #5
    Join Date
    Mar 2006
    Location
    Albany, New York
    Posts
    42
    You need to always start at the basics. Check the charge. You also need to check to see if the coil is dirty. Also check to see if the electric heat is being enabled upon defrost cycle. also be sure to check the super heat at the acculamator and not the compressor if you check the charge at the complessor you will flood the acculamator.

  6. #6
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by crooned View Post
    You need to always start at the basics. Check the charge. You also need to check to see if the coil is dirty. Also check to see if the electric heat is being enabled upon defrost cycle. also be sure to check the super heat at the acculamator and not the compressor if you check the charge at the complessor you will flood the acculamator.
    has nothing to do with electric heat, or dirty coil

    its either low on charge or defrost sensor is not mounted properly



    .

  7. #7
    Join Date
    Nov 2005
    Location
    Shreveport, Louisiana
    Posts
    2,324
    Quote Originally Posted by Airmechanical View Post
    has nothing to do with electric heat, or dirty coil

    its either low on charge or defrost sensor is not mounted properly



    .
    Mt exact same question. What does the electric heat have to do with the coil not deforsting throughly?

  8. #8
    Join Date
    Mar 2006
    Location
    Albany, New York
    Posts
    42
    Look I don't want to have this cause a problem. When heat pumps go into defrost they have electric heat inable to raise the evap temp causing the head pressure to raise making the outdoor coil defrost faster. This is only a short time frame. (If controled electronicly).
    If it has a mechanical sensor it will stop defrost when eather pressure is made or when temperature is made.
    Now when I say the coil ice forms on the middle of the coil the middle of the coil has less air flow which causes Ice to build. Normally when a heat pump is low on charge the top or bottom ice's just before the acculamator.

  9. #9
    Join Date
    Nov 2005
    Location
    Shreveport, Louisiana
    Posts
    2,324
    [QUOTE=crooned;1368368]Look I don't want to have this cause a problem. When heat pumps go into defrost they have electric heat inable to raise the evap temp causing the head pressure to raise making the outdoor coil defrost faster. This is only a short time frame. (If controled electronicly).
    If it has a mechanical sensor it will stop defrost when eather pressure is made or when temperature is made.
    Now when I say the coil ice forms on the middle of the coil the middle of the coil has less air flow which causes Ice to build. Normally when a heat pump is low on charge the top or bottom ice's just before the acculamator.[/QUO

    I am way confused now. Does the heat from the heat strips fall down in the airflow to the evaporator coil.

    All the ahu's I have worked on the heat strips are after the evaporator coil and the blower, and are there too reheat the air after it passes through the evaporator coil.

  10. #10
    Join Date
    Nov 2006
    Location
    South Carolina
    Posts
    3
    if the unit is terminating defrost on "time" cycle, its probably a refrigerant charge or refrigerant circuit issue. with a clean coil (no ice), run the system in heat mode for atleast ten minutes and use the manufacturers temp/pressure chart to see if you are close to specs with gauges located on common suction & discharge ports.

    if the unit checked properly in heat mode, force a defrost(cooling mode with outdoor fan off and strip heat on) and monitor for proper refrigerant cycle operation.

    if the unit is terminating on "temperature" before melting ice, the termination sensor is defective or mounted on the wrong tube.

    if the unit is going into defrost and the indoor thermostat satisfies (shuts the heat off and ice remains on outdoor coil) there may be too much strip heat called for in defrost.

  11. #11
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

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    Quote Originally Posted by crooned View Post
    When heat pumps go into defrost they have electric heat inable to raise the evap temp causing the head pressure to raise making the outdoor coil defrost faster.

    the reason for the electric heat energizing during the defrost cycle

    is so that you dont have cold supply air drafts while defrosting.

    it is not to expedite defrost time!

    even if you had (no) heat strips hooked up, the heat pump would still defrost

    properly, if charged correctly, sensor properly mounted, r.v. shifting properly

    and defrost board operational, also some t-stats (if) satisfied during defrost

    will not complete the defrost cycle, but if that was the case the whole

    condenser coil would still be partially frozen (not just the middle of the coil)



    .

  12. #12
    Join Date
    Mar 2006
    Location
    Florida, jacksonville
    Posts
    94
    Yeah the heat strips have nothing to do with defrost except keeping customer warm when the unit is in defrost, The unit is actually cooling the house during defrost, so hot gas in the condenser melts the ice off the coils, sounds like a low charge to me too.

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