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  1. #1
    Join Date
    Apr 2008
    Location
    Greenwood Lake, ny
    Posts
    49

    Suction line frost

    I was working on rheem/ruud 048-10 seer
    indoor coil looked clean and spotless.Cleaned outdoor unit.
    When doing my checks it would have frost up to the compressor.
    I had 55 psi on lowside/175 on highside, wb 61 db 73-74
    my superheat was between 6 and 7, ODA between 70 and 72
    I do not work on many units , I am certified , went to a class
    for a week . I do not know everything like some of you guys
    who have bin doing this for yrs. I am a oil tech and the company
    is expanding to do other things . can someone help a newbee!!!
    I want to do it right and not take 3or more hours to do it

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Did you look at both sides of the indoor coil.
    Your SH indicates either a low air flow.

    After you verify air flow, recheck your SH, and SC.


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  3. #3
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Thats low load usually, but that head is slightly higher than it should be, assuming it's been run long enough.

    How's the condenser look for cleanliness? Hows the filters?

  4. #4
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Quote Originally Posted by beenthere View Post
    Did you look at both sides of the indoor coil.
    Your SH indicates either a low air flow.

    After you verify air flow, recheck your SH, and SC.


    To go into more technical things, you will need to apply for pro membership. Get your post count up to 15 and then apply.
    Been, look at the head it's 175psig...why do you say low air flow?

  5. #5
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,989
    When doing my checks it would have frost up to the compressor.
    What was the outdoor dew point temperature?

    With light sensible & latent load on the evaporator along with possible low airflow & mismatched orifice metering device, it might allow enough liquid refrigerant to travel down the [B]suction line getting its temp below the dew point & frosting it.

    Low airflow & mismatched metering device.(?)
    An unbalanced heatload on the evaporator circuits.

    Apparent very low superheat, indicating it is feeding the E-Coil faster than the heat is boiling off the refrigerant. Could be overcharged for the existing conditions.

    Metering device not matched to the condenser, dropping suction pressure near freezing, 55-psig is about 30-F.

    Condenser pressure appears too high for the following: Did you leave enough time after washing condenser cold with cold water? Was the coil dry when readings were taken?

    Approximate 47% indoor Relative Humidity.
    A mess here, too sleepy today to think straight.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Because low air flow will decrease head.
    Yes, it could just be that thing too. But I've gone back to systems where someone said the ID coil was clean. And they did you know what. And after I cleaned the coil. Guess what I had to do.
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  7. #7
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Quote Originally Posted by beenthere View Post
    Because low air flow will decrease head.
    Yes, it could just be that thing too. But I've gone back to systems where someone said the ID coil was clean. And they did you know what. And after I cleaned the coil. Guess what I had to do.
    It's 175, high for those temps.

  8. #8
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,989
    Quote Originally Posted by beenthere View Post
    Because low air flow will decrease head.
    Yes, it could just be that thing too. But I've gone back to systems where someone said the ID coil was clean. And they did you know what. And after I cleaned the coil. Guess what I had to do.
    Recover a big refrigerant overcharge, because they had been trying to get the suction pressure up by adding charge, explains head pressure.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,120
    Quote Originally Posted by hvaclover View Post
    It's 175, high for those temps.
    Not for a 10 SEER.

    Hate to say it this way. But its only 20F over outdoor ambient.

    Now my 13 SEER at home, that would be high head.
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  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Quote Originally Posted by udarrell View Post
    Recover a big refrigerant overcharge, because they had been trying to get the suction pressure up by adding charge, explains head pressure.
    Yep.

    I don't mind a tech making a mistake. I just hate having to clean the coil he should have CLEANED.
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  11. #11
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
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    Quote Originally Posted by beenthere View Post
    Not for a 10 SEER.

    Hate to say it this way. But its only 20F over outdoor ambient.

    Now my 13 SEER at home, that would be high head.
    So which one are u calling it an overcharge or normal?

    The unit is frosting back is an indicator the system has a low load, 55psig @ 30*indicates that. Although it's not slugging according to to the SH.

    Head is too low if we assume you first post about air flow.
    20* ove assumes normal operation which this does not have.

    You would expect to see a head at this condition of 150 more realistically.

    If we had SC we could see more.

    The fact the ID and OD are so close also means there is very little heat to be extracted from the air also which would result in a head lower than 175.

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Low air flow gives low SH, he's only running 6 to 7*
    His ID WB, indicates his SH should be more around 14 to 15*
    With his vapor pressure at 55PSIG, There is a chance on low charge, if he isn'r letting the coil thaw before checking readings.

    Low air flow, and someone has probably added some gas to the system in an attemp to stop the freezing of the coil.
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  13. #13
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
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    6,058
    Quote Originally Posted by beenthere View Post
    Low air flow gives low SH, he's only running 6 to 7*
    His ID WB, indicates his SH should be more around 14 to 15*
    With his vapor pressure at 55PSIG, There is a chance on low charge, if he isn'r letting the coil thaw before checking readings.

    Low air flow, and someone has probably added some gas to the system in an attemp to stop the freezing of the coil.
    Like I was saying , abnormally hi head. The ratio between 55psig and 175psig is too high.

    Course would be nice to know if he cleaned cond or changed filters.

    Under side of coil was a good point Been. i don't want to think about how many times that get's overlooked

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