Avoiding sludge buildup in window ac units
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  1. #1
    Join Date
    May 2013
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    5

    Avoiding sludge buildup in window ac units

    So in my NY apartment I took down our two ac units to clean them. The front and rear fins and ac coils were very easy to get clean using a little soap and the garden hose.

    However, on both units (different brands), on the rear set of coils, not the very exterior, but just behind the fan, there is sludge buildup that I cannot for the life of me remove. It is just behind the fan stuck on the fins.

    I have tried spraying it out from the inside out. I have tried spraying it inward. I have used ac coil cleaning spray foam and hot garden hose water. It just will not come off. It moves around a bit but still sticks to the fins.

    I ended up purchasing two new units and would like some advice on how to avoid that buildup in the first place, as well as a better way to clean it, if I did it wrong.

    Of course I know now to keep the mesh filter very clean. I plan on cleaning that every couple days.

    What about using a breathable AC cover in the winter? Will that help much in preventing sludge buildup on the fins back there? Does much dust and dirt accumulate in the unit during NON use?

    When I clean the unit, is it best to use compressed air to blow it out first in the areas that I cannot get to with the vacuum? I wondered if I should blow it out first and then wash it. Because I cannot get to the coils right behind the fan with the vacuum or even my hands.

    Any thoughts would be appreciated.

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    9,697
    anything built up on the outdoor coils would only come in while the units are running . i don't think covering them would do much good.
    as far as cleaning them it may be possible to partially remove the coil and get to it with a brush.

  3. #3
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    I think most window units have slingers that fling evaporator water onto the rear of the coil to aide cooling and get ride of the condensate. This could easily cause sludge to build-up. You can get tables to place in the condensate pan that will reduce slime.

    The cover might make the problem worse since it will hold in moisture. I think most all condenser covers actually reduce equipent life because they trap in moisture. 1/2 covers are OK for splits system if you have a lot of trees in a 4 season climate coastal location. I suppose covers help prevent the paint form fading. If they were more like a Tyvek material and more breathable, it woudl help. There you go, I need to design a line of disposeable, maybe black, grey or brown tyvek AC units covers. Heck, you could even print you favorite sports team logo on it.


    If the units are on the east or north of the building or in NYC the "urban forest" of endless shade... where the sun never dries out the unit... the problem will also be worse.

  4. #4
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,970
    When you say " However, on both units (different brands), on the rear set of coils, not the very exterior, but just behind the fan, there is sludge buildup that I cannot for the life of me remove. It is just behind the fan stuck on the fins. " are you talking about the coil that when looking at the back of the unit from outside, the sludge is on the other side of this coil?

    If that's the case then you've run up against what I like to call "designed for failure" engineering. The units are put together in such a way that most are next to impossible to easily clean that backside of that coil. That outside coil has air pushed through it so that it exits the outside back of the unit. This air is pulled in through the ventilation ribs built into the outside of the cabinet. Along with the air is the "stuff" floating in the air which can include pollen, dirt (of many different types), floating seeds from trees and plants, concrete dust if there was construction going on and the list goes on. I think every window unit also uses the outside fan to pick up condensate water and fling/blow that through the coil to gain a bit of added efficiency. You take the mix of air-born things and add a little moisture and heat (that coil gets hot) and you've got a perfect setup for making some really unique "cement".

    You want to clean these by "flushing" from the outside to the inside of the coil. Trouble is when you do this, and the crude starts coming off, there is really no good way for that to be drained out unless the unit you have has a plug that allows that section of the bottom of the case to be drained easily. If you still have the old units experiment with different household cleaning fluids to find which one best dissolves the "cement" bond. A hand spray bottle should be all you need and of course patience. Each area of the country and even your city may have different components that make up the problem.

    I had a 120 room motel that had pine forest all around it. The pine trees would shed clouds of yellow pollen in the early summer..... talk about something that would stick and plug up a coil! We experimented and found a natural oil based cleaner would easily dissolve the yellow mud on the back of the coils. We also converted the units to drain their condensate water out of them instead of "flinging" it onto the coil. Yes, they lost a bit of efficiency, but they also avoided 120 rooms of AC units that within a few days time would almost to a unit quit cooling.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  5. #5
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
    Posts
    3,003
    is there a Chinese restaurant or family that cooks a lot nearby?

    GREASE is very difficult to clean from a condenser. there are special grease cutter cleaners that sort of work...
    The TRUE highest cost system is the system not installed properly...
    The three big summer hearththrobs...
    Mel Gibson
    Dwane Johnson
    The A/C repairman

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,884
    The slinger does a lot of damage. It sprays water on the coil and a wet coil collects dust and cakes it on the coil. After time, you will have a hell of a time getting it off as you have found. They do it so their unit doesn't drip on a NYC sidewalk from 10 floors up. But if dripping doesn't hurt anything, drill a hole at the lowest point and let it drip. Of course don't drill into a refrigerant line or coil

  7. #7
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    the more often it is cleaned the easier it will be (its allways easier to keep them clean from new)

  8. #8
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    Also they are desighned that way so they can be cleaned in place and or without taking them apart . Spray directly at into the outside coil as often as possible and if they are being removed for the winter months allways clean them upon removing , not after storage

  9. #9
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,607
    take them to the carwash
    We really need change now

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by catmanacman View Post
    take them to the carwash
    ..or scrap yard. We have locations were these units are disposeable and get repalced on about a 6 month basis. Sadly, a Minisplit probably wouldn't last more than 5 years in these locations, so guess what is cheaper? A $$$ AC unit or a $$$$ mini split? In a perfect world, we'd have chilled water air handlers with SS coils. Oh well.

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