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Carrier ahu

Discussion in 'Commercial' started by pintofstout, Sep 1, 2017.

  1. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    So i went to help out today on a drain pan replacement on a carrier ahu. Tech said this is the fifth replacement.

    It's the style where the coil is slanted across the inside of the unit and relies on air to keep condensation attached to the face of the coil, rather then dripping off.

    The evaporator coil is in the return prior to the motor.

    3 ton condensing unit.

    I'm struggling to make sense of the situation. I believe that the problem is not cracking drain pans, i believe that the water is either pulling off of or dripping off of the coil.

    The manual gives me a pressure drop across the coil to calculate air flow. Basically the lowest available number was a 1" drop across a wet coil, which was exactly what i had. But, that correlates to 3000 cfm. I only have three tons of cooling. So, it's oversized? Uhhh, ok but the others are matched up like that and don't leak.

    I was thinking more like LOW air flow. The discharge air line has a lousy .2 inches of static. Prior to the heating coil (or directly after the fan) i read .4 inches.

    In the returnvcabinet, right by the blower, -1.1" wc. Downstream a foot, immediately before the coil, i measure -.7" wc. Working back, beyond the coil, -.6". After the filters, -.45".

    That's an esp of .65. Fan motor pulling a little more then 80% RLA. Max esp was 2.6.

    Ran cooling which proved to be non conclusive. I had 51 degree discharge air with 67 degree return air. Sight glass was flashing like crazy and i did not gauge up. Liquid line was cold, seemed like lack of load caused flashing and i ignored it. I'm told it is not freezing up.

    Someone please fix this. Or ...just tell me exactly how and I'll do the tools part.

    I believe Mr. Solid is of the Carrier persuasion? It's a 40rm-12


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    Last edited: Sep 1, 2017
  2. R2D2-TX

    R2D2-TX New Member

    Messages:
    415
    10 years ago some not all Carrier air handlers with a slant coil would drop condensate and the factory's fix was a "drip eliminator " ... it would attach to the top of the evaporator coil and just lay in the condensate pan.. easy to install and it does work... hope this helps✌️
     
  3. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    Was it basically an inclined plate that ferries water to the drain pan then? These units are ten years old


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  4. R2D2-TX

    R2D2-TX New Member

    Messages:
    415
    Yes exactly... it is aluminum with U channels that catch the condensate and carries it to the drain pan
     
  5. 404eh

    404eh New Member

    Messages:
    190
    Is there a trap on the drain
     
    Anita sannich likes this.
  6. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    I've been reading that a film of oil on these will cause water to fall off the coil. I'm sceptical that my coil got a coating of oil, but then some of the threads i read were pretty damn compelling. Definitely going to have the tech try cleaning it.


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  7. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    Ok great maybe i can have the metal shop make one.


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  8. frozensolid

    frozensolid Psychologist's Dream

    Messages:
    12,216
    Location:
    Earth
    Are you telling me you have a 3 ton condenser on a ten ton coil and it actually is producing condensate? 40 rm 12 = 10 ton. :confused:

    40rm always come with the sheave set for max air flow. And they many times leak. Open the sheave up a bit and it usually corrects problem.
     
  9. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    I dunno frozen, that's a ten ton AHU? The model number of the condensing unit started with 36 or 38 and i took that to mean it was a little over 3 tons.

    The sheave was locked solid somewhere in the middle, we already have a replacement on order. We paused the job pending that part.


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  10. R2D2-TX

    R2D2-TX New Member

    Messages:
    415
    Carrier should be able to order you one ....that is not something a metal shop can make unless they know exactly what it is. I have picked them up before at the carrier supply house... factory made
     
  11. frozensolid

    frozensolid Psychologist's Dream

    Messages:
    12,216
    Location:
    Earth
    38AUZ (tonage here)
     
  12. R2D2-TX

    R2D2-TX New Member

    Messages:
    415
    Most likely the model number starts with 38... that is not the tonnage.
    Not sure how far into the model number the tonnage is... but I know it's not the first two. 38 may be a style...
     
  13. frozensolid

    frozensolid Psychologist's Dream

    Messages:
    12,216
    Location:
    Earth
    Correction rm is r-22 auz is 410 I don't offhand remember the R22 cond number but it does start with 38
     
  14. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    I had a feeling i was getting that wrong. So it looks like I've got about 3000 cfm.


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  15. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    Ok thank you


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  16. 404eh

    404eh New Member

    Messages:
    190
    20170817_152412.jpg
    Had the same problem cause this trap was backwards
     
    Chuck likes this.
  17. frozensolid

    frozensolid Psychologist's Dream

    Messages:
    12,216
    Location:
    Earth
    Likely not relevant but that pan is drainable from either side. The screws holding the drain pan are shipped loose with slotted holes. You are supposed to lift the pan on the opposite side from the piped drain for slope and field tighten.

    And if they did not cap the unused hole it would be like having no trap at all.

    Hope you figure it out.
     
  18. 404eh

    404eh New Member

    Messages:
    190
    Goodman does that too
     
  19. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    These have been in for ten years- believe me i didn't gather all that information without checking the trap! Lol there cool


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  20. pintofstout

    pintofstout New Member

    Messages:
    1,520
    Location:
    Olean, NY
    Yeah they plugged the hole in ALL FIVE drain pans that they replaced on this unit. Five. Five replacements.


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