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Thread: restriction??

  1. #1
    Join Date
    Feb 2013
    Location
    Summerville SC
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    117

    restriction??

    im working on a 3 ton ruud rooftop package. last week I found the system iced up in cooling mode on about a 75 degree day. checked charge seemed good by superheat but my suction pressure was a little low right about 60-65 psig(r22 by the way). my head pressure was at 190. superheat was 12 degrees. so I then went into checking airflow, cleaned blower and ID coil. checked filter and return duct static. .3 of return static and .24 on supply. well got to that point and was sent on an emergency call that was more important. finally got back late this afternoon to see what I could find and in heating mode im seeing really high head pressure (275-300). compressor is going into relief to drop the pressure. true suction is running about 60-65 with around 14 degrees of superheat. then of course I got called back off again.(for those wondering what kind of company I work for...this unit just serves a warehouse and really isn't important to the owner and the store manager is in no rush to have it fixed if at all). well anyways I was thinking next blue moon when I get out there to check temp drop across drier and then if nothing there I will probably pull the charge and weigh back in what the nameplate calls for??? any suggestions?
    "only 2 tools any man needs is wd40 and duct tape. if it moves and it shouldn't use the duct tape. if it doesn't move and should, use the wd40" -unknown

  2. #2
    Join Date
    Feb 2013
    Location
    Summerville SC
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    117
    forgot to add that OD temp today was around 55 degrees and return air temp was 68 degrees
    "only 2 tools any man needs is wd40 and duct tape. if it moves and it shouldn't use the duct tape. if it doesn't move and should, use the wd40" -unknown

  3. #3
    Join Date
    Jun 2012
    Location
    Rising Sun, Maryland, United States
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    110
    Txv or piston partially clogged? Idk just a shot in the dark

  4. #4
    Join Date
    Feb 2013
    Location
    Summerville SC
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    haven't had the time to actually break anything down. ive been at the site a combined hour and a half maybe. kind of annoying when your trying to fix a system......
    "only 2 tools any man needs is wd40 and duct tape. if it moves and it shouldn't use the duct tape. if it doesn't move and should, use the wd40" -unknown

  5. #5
    Join Date
    Jun 2012
    Location
    Rising Sun, Maryland, United States
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    110
    Yeah I hear ya. I mean out of everything you said you checked that's the only thing that comes to mind that would restrict the suction pressures

  6. #6
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,914
    Subcooling? entering/leaving air WB and DB?
    If more government is the answer, then it's a really stupid question.

  7. #7
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    Feb 2013
    Location
    Summerville SC
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    Yea i havent been doin service but a couple years if that and refrigeration is my weak side..figured id start back at what i mentioned earlier with the drier.it does have a outdoor txv which i have seen them stick (stuck mid position maybe, not causing pumpdown like a indoor would)and cause the lower suction in cooling but never payed attention to what happened in heating.

  8. #8
    Join Date
    Feb 2013
    Location
    Summerville SC
    Posts
    117
    Did not think to take subcooling because it a fixed orifice metering device.i couldnt remember exact wetbulb temps but dry bulbs were 74 ent and 57 lvg in cooling.heating is 68 ent 85 lvg w/o strips

  9. #9
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    Jul 2009
    Location
    Columbia, MD
    Posts
    3,790
    pressures seem right for 55*oat. try bumping fan speed up for heating.

  10. #10
    Join Date
    Feb 2013
    Location
    Summerville SC
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    117
    fan speed is on high.i moved it the first time out to ensure it was moving air but barely helped if at all
    "only 2 tools any man needs is wd40 and duct tape. if it moves and it shouldn't use the duct tape. if it doesn't move and should, use the wd40" -unknown

  11. #11
    Join Date
    Jul 2005
    Posts
    5,380
    You wouldn't typically be looking for a restriction with 12° SH and normal to low head pressure. You also have to be careful when relying on static pressure readings on older units. If the evaporator coil is dirty, then your static pressure will be lower than normal, as will your airflow. With low suction and normal to low SH airflow is most likely the problem.

  12. #12
    Join Date
    Feb 2013
    Location
    Summerville SC
    Posts
    117
    that was my original thought.it has the zig zag type coil which I know has to be a devil on airflow.i did clean the evaporator thoroughly and the blower as well. I guess if I wanted to further investigate that I should have gotten pressure drop across coil. I told the service manager that everything from what I know leads to airflow and he disagrees. he said the unit has always ran fine so he seems to thinks theres more to it
    "only 2 tools any man needs is wd40 and duct tape. if it moves and it shouldn't use the duct tape. if it doesn't move and should, use the wd40" -unknown

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,914
    Quote Originally Posted by SCtech33 View Post
    Did not think to take subcooling because it a fixed orifice metering device.i couldnt remember exact wetbulb temps but dry bulbs were 74 ent and 57 lvg in cooling.heating is 68 ent 85 lvg w/o strips
    You should get in the habit of checking both SH and SC. You can't reliably diagnose a refrigerant side problem without the whole picture.

    Don't be that blind squirrel.
    If more government is the answer, then it's a really stupid question.

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