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Thread: Lennox 40 ton?

  1. #1
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    Lennox 40 ton?

    This is a rooftop package, air cooled, 4 scrolls, 4 circuits, the main fan has a vfd.
    Lennox 40 ton, R22, VAV system less than 5 years old.
    Return 80F, supply 65F with 3 circuits on, Liquid line temps 105-110F
    ambient 104F

    Problem: low suction pressure 50psi on all 4 circuits, warm suction lines 70-85F
    average to high head pressure 250-350psi (different on each circuit, thats the range I see, 275, 345, 360, 300.
    high discharge temps on all 4 compressors 225-250F at the compressor.
    Each one runs different.

    This is with the condenser fans running, proper rotation, main fan at approx 40 hz.
    Work was done by a previous company, so I dont know what the charge is, if it is blended etc.

    I feel like its a refrigerant issue, since I doubt all 4 txv's are bad. I am going to recover the charge one circuit at a time, and measure the temp/pressure relation, and go from there.

    Am I missing something? filters clean, condenser clean.
    I have never witnessed such a new piece of equipment with such strange symptoms on all 4 circuits.

  2. #2
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    Its sounds like a systemic issue but It might just be a low charge on all circuits and maybe some noncondesables.

    Probably your best bet to pull the charge and start with a good vacuum and fresh R 22 weighed in.

    I'm guessing the VFD is controlling static.

  3. #3
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    1.5" static. I would prefer to blow off the R22 non condensables, (20lbs times 4=80lbs)but I feel like it could be blended with something 410A? I attempted to add some R22, but the suction pressure didnt budge. I also expected the discharge temp to drop, but it didnt.

    I have had a txv get stuck, which showed similar symptoms, but having all 4 circuits acting so weird is what gets me.

  4. #4
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    how sure are you the condenser is clean? If you did not wash it I would start there. Helped a tech the other day by phone where he weighed in the charge on a coil that looked clean but when he cleaned it everything came in line.

  5. #5
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    Quote Originally Posted by Retread View Post
    how sure are you the condenser is clean? If you did not wash it I would start there. Helped a tech the other day by phone where he weighed in the charge on a coil that looked clean but when he cleaned it everything came in line.
    Dirty condensers wouldn't cause his suction to dive and neither would a mix of 410A with R22.

    Non condensables would be trapped at the highest point in the condenser lowering effective condenser coil area causing high head, high discharge temp and low suction.

  6. #6
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    Quote Originally Posted by Retread View Post
    how sure are you the condenser is clean? If you did not wash it I would start there. Helped a tech the other day by phone where he weighed in the charge on a coil that looked clean but when he cleaned it everything came in line.
    100% positive its clean.
    So Six, are you feeling all 4 txv's are stuck mostly closed?

    I may have to force my VAV's open and up the fan to 60HZ to rule out airflow.

  7. #7
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    With those suction lines being 70 to 85 degrees I really doubt it.

    A txv that's not feeding all other things being ok will ice up at the distributor.

    Low airflow will cause the distributor to ice up and the suction lines to ice up also.

    How about recover one circuit into a clean reclaim jug and use a PT chart to check against ambient temp for non condensables ?

  8. #8
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    There was ice after the txvs on the distributors. I also thought the warm suction lines didnt indicate airflow.
    I have seen similar symptoms with clogged screens on the txvs, warm suction temp, low suction pressures.
    Thats my plan, try recovering one circuit and measuring it, then going from there. Waiting for my quote to be approved.

  9. #9
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    What is your sub cooling? High sub cool with high super heat = plugged txv screen. Manually open a txv and check your pressures and temps. Does this unit have hot gas?
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  10. #10
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    no hot gas, high superheat and subcooling. Will find out tomorrow, maybe the factory overheated the txv's. I feel like its the TXV screens. The factory purges nitrogen, or is supposed to, right?

  11. #11
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    I recently had a couple LGA240's that I replaced 4 powerheads on one and 3 on the other. There are no screens on the Sporlan OEM vale. If you dont have a drop across the drier, its the valve.

  12. #12
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    This is an SGA480. I will go the powerhead route tomorrow. And correct the charge back to the nameplate.

  13. #13
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    Quote Originally Posted by B1978 View Post
    no hot gas, high superheat and subcooling. Will find out tomorrow, maybe the factory overheated the txv's. I feel like its the TXV screens. The factory purges nitrogen, or is supposed to, right?
    If you have high sub cooling and a hot suction line, you have txv issues. The sub cooling means there is available cooling that you are not using. Why is it consistent on all the circuits? Check the power heads, and numbers on the valves. Lennox has good tech support, maybe they already know about the issue.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

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