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  1. #1
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    Trane roof top unit freezing up .

    trane model # SFHGD114HTH8CE7D300100DEOGKLONOT0000 circuit one is freezing up . checked for a leak none found . Put the gauges on. outside air temp 63 degrees F. high side 175psig, low side 45 psig. Pulled the whole charge of 145 lbs so it was overcharged. It should be 112 lbs. So I charged to the correct weight and it still is freezing up . Air flow is good. Filters are new. I have no bubbles at the site glass. Return air temp. 69 degrees , Super heat was 25 degrees and subcooling was 15 degrees. all compressors running and all condenser fans . I did notice that the frost stat was shutting off the wrong circuit . circuit one was freezing and it would shut off circuit 2 but I still don't think it should be freezing up. Took the temp of liquid line filter before and after it was the same so no restriction there.

    Any help would be great!

  2. #2
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    when its 63 deg outside , you either need fan control , or a freeze stat on the correct compressor …


    Doesn't this have adjustable TXV's …. maybe open that valve 1 turn see what happens to your numbers, assuming the drier is good

    Hold that bulb in your hand to see if that's working too


    Good chance the drier is the culprit tho … and someone threw gas in there to compensate .. and the Einstein also switched the freeze stat wires

  3. #3
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    Jan 2014
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    Partially block the OD coil to get the head pressure up to 225 PSI + low side should follow when your checking at that low a OD temperature. No load on the unit. Even your ID return temperature is low at 69 degree.

    ID inlet side of the coil really clean?

    assuming this is a packaged unit, does this unit have a economizer?

    Of all the condensor fans, there is not a pressurestat or OD temperature controller on them, hot gas bypass? No capacity control on compressors. How low a OD temperature do these unit run on mechanical Cooling?

    Guessing the Liquid Line at those pressures on that circuit is cool or cold to the touch? Need to get it warm.
    Last edited by Bazooka Joey; 09-13-2018 at 09:42 PM.

  4. #4
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    At 69 degree room/return temperature why are all compressors and condensor fans running? Shouldn't you be in low stage no? What indoor temperature are you trying to maintain to have everything running b@lls to walls?

  5. #5
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    May 2015
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    Thread Starter
    Supply set point is 55 degrees F. To supply a large amount of vavs

  6. #6
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    What happens when it's say 60 degree or a tad less OD temperature. Isn't there any type of existing head pressure control? If no Head Pressure Control, what does the manufacture literature or Trane Tech. Rep. say in regards to the lowest OD temperature you can run this unit without those controls?

    Guessing this system had problems with this before if the freezestat was mixed up and on the wrong coil. You got the TXV sensing bulb at least on the correct coil?

  7. #7
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    The Tranes I've worked on have head pressure controls. First and second fans come on with head pressure control. Second fan is locked on thru Auxiliary contractor on compressor contractor. First fan cycles on the head pressure control that originally turned both fans on. Also if there is an economizer, it should lock out the compressors or the just lag compressor on low ambient. Look for an unplugged sensor going to the economizer actuator. I've seen ones where the economizer failed, and a lazy technician just unplugged the sensor and walked away from it.
    Retired, after 43 Years

  8. #8
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    Dec 2004
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    Quote Originally Posted by bulldog53207 View Post
    trane model # SFHGD114HTH8CE7D300100DEOGKLONOT0000 circuit one is freezing up . checked for a leak none found . Put the gauges on. outside air temp 63 degrees F. high side 175psig, low side 45 psig. Pulled the whole charge of 145 lbs so it was overcharged. It should be 112 lbs. So I charged to the correct weight and it still is freezing up . Air flow is good. Filters are new. I have no bubbles at the site glass. Return air temp. 69 degrees , Super heat was 25 degrees and subcooling was 15 degrees. all compressors running and all condenser fans . I did notice that the frost stat was shutting off the wrong circuit . circuit one was freezing and it would shut off circuit 2 but I still don't think it should be freezing up. Took the temp of liquid line filter before and after it was the same so no restriction there.

    Any help would be great!
    You need head pressure controls, that unit should have it, perhaps its not working right, or has been bypassed.

    Also most Trane VAV units have a control scheme for discharge air reset based on OA or return air temp that can be activated. At 63 OA and 69 return, chances are you dont need 55 degree discharge, might get away with 58 or 60 degrees. That couple of degrees will help tremendously, as the compressors can stage down. In all reality, they should stage down now, as its not 95 out, and they are struggling with the load.

    Look for a LL restriction, or dirty evap coils, loose belts, worn drive sheives, or indoor VAV zones that are open too far, and are not throttling down, etc... lots of variables.

    Also 25 degree SH is on the high end.


    Sent from my iPhone using Tapatalk

  9. #9
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    Try the cardboard on condenser first , or unhook 2 fans

    i've had driers with a slight clog and not show any temp diff

    Its no guarantee , but it's a cheap easy attempt

    And if anyone gives you any crap , tellum Snapper said if they are so smart why don't They come fix it. !
    Last edited by Snapperhead; 09-14-2018 at 07:44 PM.

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  11. #10
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    Jul 2015
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    You say airflow is good, but what are you basing this off of? All compressors and fans running on a 63 degree day seems way off. Assuming this unit has a VFD ( I can't find anything but a parts breakdown from Trane) I would assume that not all VAV boxes are calling for cooling, and the fan is running at far less than 100%, especially given your 69 degree return temp. All 6 compressors running with less than 100% fan likely isn't enough airflow. If no VFD, is there a bypass?

    What are your pressures, SH&SC of circuit 2 while all of this is going on? If 1 was wildly over-charged and freezing up with all 6 compressors running, I would expect a properly charged circuit 2 to also freeze up...

    What is your actual measured supply air temp as the unit stages up (with a temp probe, not the on-board sensors)? What happens when you disable the second stage of cooling on each circuit (or circuit 2 altogether)?

    Did your pressures, SH & SC change after you removed and weighed back in the refrigerant? Does it trip off on low pressure now that it's not wildly over-charged?

    Does this unit have hot gas bypass?

    I'm leaning towards a bad TXV or plugged distributor/tubes. Does it look like the TXV has ever been replaced? Another possibility is an oil-logged evaporator, but that's just me drawing straws based on little information.

  12. #11
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    Just unhook the wires to that compressor , write on the ticket performed general maint , and let the next guy figure it out next summer

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  14. #12
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    Another thing, do you have a Main in Duct Hydronic Heating Coil? I heard a tech. talking about one of those coils being completely clogged with duct sound line shredding and ended up imbedded in that coil. He showed me pictures of it and it looked like I was looking at a solid wall of sound liner.
    Retired, after 43 Years

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  16. #13
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    Apr 2012
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    virginia
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    you need some air side measurements to diagnose further. Your superheat and subcooling seem a little high which may be a restriction in the refrigerant side. low air flow and low loads can cause freezing too.

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