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Unico coil dripping water, missing the pan

I'm stumped, I have good customer with a coil dripping, the local rep says it's extremely rare for a coil to drip. This is a horz 3 ton, it's about 12 years old. It's a very long story, the AHU hasn't been used in 11 of those 12 years. There has been some remodeling lately/ new sheetrock. I called Unico twice, left messages twice, never heard back. If there are any Unico experts out there please comment. I asked the local rep if there was a pressure drop chart and he didn't think so. I can't 'see' any debris on the coil. There is a HW coil before the ac coil.

Thanks, Gary
Gary Wilson

Wilson Services, Inc

Northampton, MA

Comments

  • njtommynjtommy Member Posts: 1,062
    I do believe they make a drip shelf or pan to block the water from being pulled off the coil. I had to install one about 8 years ago. Do you have model and s/n? I can ask my rep to see what they say.
  • JUGHNEJUGHNE Member Posts: 3,266
    Is there SR sanding dust on the coil?? Hard to wash off without pulling the coil and taking it outside.

    I had that problem with a counter flow AC. Water would gather in the lower supply plenum and drip into the basement.
    IIRC I wetted the inlet side (top) of the coil with a dishwashing soap mix. That seemed to make the water cling to the fins and make it down to the pan.....but check for SR dust first or you might have white mud/clay formed.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 2,488
    edited August 23
    If the air velocity across the coil exceeds around 600 FPM you will pull water off the coil. Actually 500-550 FPM is recommended.

    Slowing the air flow down may be a temporary fix if you can avoid low superheat or flooding the compressor

    If the coil is dirty maybe you can cut it out and remove /reinstall.
    3 tons ought to be1200 cfm minimum. If the coil is dirty the cfm would probably be low with a high velocity.

    what sort of TD do you have across the coil??
  • GWGW Member Posts: 2,583
    njtommy said:

    I do believe they make a drip shelf or pan to block the water from being pulled off the coil. I had to install one about 8 years ago. Do you have model and s/n? I can ask my rep to see what they say.

    Thanks Tommy I will get that asap, this week hopefully. We've been busy with a big radiant project at the same home and the ac has been a small after the fact issue.
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • GWGW Member Posts: 2,583
    JUGHNE said:

    Is there SR sanding dust on the coil?? Hard to wash off without pulling the coil and taking it outside.

    I had that problem with a counter flow AC. Water would gather in the lower supply plenum and drip into the basement.
    IIRC I wetted the inlet side (top) of the coil with a dishwashing soap mix. That seemed to make the water cling to the fins and make it down to the pan.....but check for SR dust first or you might have white mud/clay formed.

    Thanks J there is no visible goop at all. The drips are literally falling off the coil on the 'incoming' side of the coil. If the water would cling i would be all set.
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • GWGW Member Posts: 2,583

    If the air velocity across the coil exceeds around 600 FPM you will pull water off the coil. Actually 500-550 FPM is recommended.

    Slowing the air flow down may be a temporary fix if you can avoid low superheat or flooding the compressor

    If the coil is dirty maybe you can cut it out and remove /reinstall.
    3 tons ought to be1200 cfm minimum. If the coil is dirty the cfm would probably be low with a high velocity.

    what sort of TD do you have across the coil??

    Ed, that's the thing, it's dripping off the 'incoming' side of the coil, it's not flying off of the downstream side of the coil

    Unico is 200 per ton, or 600 CFM in this case. I wonder if increasing air flow might warm the coil a tad, this is a 3-3.5 ton coil. But still, should not be happening.

    (I feel ya Chris)

    I'll need to go back and get more numbers; I don't have the del t at this moment. I was getting those numbers when i was there but didn't log them

    Thanks, Gary
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • Dan FoleyDan Foley Member Posts: 1,051
    Gary,

    If water is dropping off the coil, as opposed to blow off, you have a dirty coil.

    Try spraying it with green coil cleaner and flushing with water. That will take care of dirt and dust between the fins.

    Hopefully you don't have Sheetrock dust beteeen the fins. Once this dust gets wet with condensate and then dries, it hardens like concrete and you will not get it out. That is why we will not allow AC to run on our construction jobs until interior finishes are complete.
  • GWGW Member Posts: 2,583
    Thanks Dan, I was very clear about this in the beginning, but I'm not sure what did nor didn't happen when the sheet rockers where there this past early spring
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • JUGHNEJUGHNE Member Posts: 3,266
    Never have seen a Unico system.
    But all plain vanilla AC's that had a horizontal coil all had a drip pan that fit under the entire coil, no mater what direction it pointed.
    It came with all universal coils and I have collected some drain pans for horizontal use. The A coil still had the standard upflow drainpan installed, it stayed in place and if horizontal then the big pan was used.
    With these the upstream part of the coil could drip all it wanted and would end up in the pan.

    Is this missing the horizontal drip pan?
  • GWGW Member Posts: 2,583
    there is no pan catching the drip, I'll need to look into that. Or maybe make a simple pan to grab the drips
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • unclejohnunclejohn Member Posts: 909
    Is there a trap on the drain.
  • JUGHNEJUGHNE Member Posts: 3,266
    Is this an A coil or a slab on a slope?
  • GWGW Member Posts: 2,583
    John It's trapped, the dripping doesn't seem to involve piping however

    J it's a tilted slab

    I guess I need to see what's involved to get a pan. I did a bunch of Unico back 10/15 years ago. Never seen a pan
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • JUGHNEJUGHNE Member Posts: 3,266
    It seems like there is not enough air flow to push the condensate thru the coil to run down the back of the coil. Lack of air flow or plugged coil??
  • GWGW Member Posts: 2,583
    Possible, a pressure drop chart would be nice.
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • HVACNUTHVACNUT Member Posts: 646
    > @GW said:
    >
    > I guess I need to see what's involved to get a pan. I did a bunch of Unico back 10/15 years ago. Never seen a pan
    >
    > Which is typical. Just a tray. As an example, if its a horizontal left, blower compartment on the left. Coil mounted at 10:00 o'clock to 4:00 o'clock? Condensate should follow the fins nicely

    Sounds like a partially blocked coil. The condensate is hitting obstructions and dropping off.
  • AMservicesAMservices Member Posts: 222
    Is this unico blowing horizontal left or horizontal right? Unico only allows horizontal left installations.
    I've seen some crazy condensate problems with high velocity systems. Mostly with the "High Velocity" brand. But I have talked about this with unico tech support and they said it has to be blowing left to prevent draining problems.
    Just a thought
  • GWGW Member Posts: 2,583
    Thanks, it's blowing left.
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • unclejohnunclejohn Member Posts: 909
    Where is it leaking from? The bottom of the unit? If there is no pan then most likely there never was. Check your charge and make sure the coil is wet from top to bottom. A dry coil will shed water.
  • unclejohnunclejohn Member Posts: 909
    I finally read your post correctly. The pan isn't missing the water is not falling into the pan. So check the charge and make sure coil is wet. If it is simple fix is get some sheet metal and extend out to where the water falls and all done.
  • GWGW Member Posts: 2,583
    Thanks uncle J will double check
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • GWGW Member Posts: 2,583
    Tommy if you can check with your guy,

    MC3642C
    0404A142370

    Thanks
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • Kybeans403Kybeans403 Member Posts: 15
    Were you able to resolve the issue? Can't quite tell from above posts. We work primarily with Unico and have been installing sdhv systems for 20 + years and would love to help if needed.
  • GWGW Member Posts: 2,583
    No, still an issue
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • Kybeans403Kybeans403 Member Posts: 15
    Please send me an email at kmorrell@sila.com and we will fix this!
  • Big EdBig Ed Member Posts: 869
    I would double check the trap .. Assuming you already checked the trap and passage are clear.... An improperly installed trap would hold back the condensate from draining .. The vent belongs after the trap. , any opening before the trap needs to be plugged ... The trap is needed when the coil is on the negative side of the blower ... It pulls the condensate out with capulay action .. Air rushing in before the trap would break this action , Add to the fact it's an High V system....

    Proper size return is important ,check the book thinking 16" for three ton .. Smaller then you you would think , but check the instal instructions. You have to go by the book to make them work ...

    I have enough experience to know , that I dont know it all
  • Kybeans403Kybeans403 Member Posts: 15
    3 ton Unico's use an 18" return duct. I have noticed over the years that the pressure from the fan actually does hold back the condensate quite a bit and will drain fully when system cycles off. We typically pitch our units roughly 2" back towards drain outlet. Every once in a while you'll find the drain port pitched up a bit back towards the pan (firstCo has same issue) if you try and bend it, the pans are metal and you'll break em....

    You should still have a stainless drip pan under the return side of the evap coil.
  • GWGW Member Posts: 2,583
    It’s not the pan it’s the droplets falling from the slant coil and missing the skinny pan.
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
  • Dan FoleyDan Foley Member Posts: 1,051
    Gary,

    Try cleaning the coil with coil cleaner. It may look clean on the face but dirt and oil get trapped between the fins. This can cause dripping and blow off. A good clean and rinse may be the solution.
  • Kybeans403Kybeans403 Member Posts: 15
    Picture of return side of evap?
  • GWGW Member Posts: 2,583
    Thanks I will take a before and after pic of the inlet side of the coil. It may be some time before we get back on this. This job was started in 03 or 04 I think. Now he just Sheetrocked this past summer
    Gary Wilson

    Wilson Services, Inc

    Northampton, MA
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