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Keeping a mini split clean and sanitary

As a service technician I see more ductless systems every year. They certainly aren't my favorite thing to have to work on. A common problem I see is heavy buildup of of black "biological growth "on the inside of the indoor units, especially on the blower wheel.
We currently clean these units with a bib kit, and pump sprayers with a chemical solution in it. The process would work better with a coil jet sprayer, but either way it can be a messy time consuming job.
Is there better way to clean these units? I've looked into ultraviolet lights as way to prevent contamination. Some units such as Carriers have a self cleaning mode built in, but that requires the homeowner to use it. That never happens so I'm still unsure of its effectiveness.


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,695
    The "Bib Kit" is the best thing I have found. along with the pump with a Sprayer nozzle to lightly "Pressure Wash" the coil and fan. Takes less them than removing the screws and accessing the interior with a washcloth. After doing that on one unit and taking over 4 hours to thoroughly clean the unit, I decided to try the bib/funnel idea and was completely sold. Now you need to teach your staff to use it properly. I find that is more of a challenge than anything. Getting the tech to take pride in doing the maintenance properly is often difficult.

    Tools don't always make for good results. the person using the tool is the most important part of the job.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • clammy
    clammy Member Posts: 3,015
    It seems to me that the mini splits that where filthy where usually neglected and the filter never removed and cleaned and in what seems a lot of case homes that could use a good cleaning ( hi dust and animal dander ) home w a lot of pets seemed to fair worse . While I ve been in a few that never end up being very dirty . I think a lot has to do w the air quality inside the home . In cleaning them its all the same ,I started using anti fungal condensate pan treatment and it has seems to curb the worse ones a little bit ,I usually use the bib and a calogon non rinse evap cleaner and have some have said cleaned within a inch of its life , I,ll usually take the cover outdoor hose it off w water then spray w spray nine ,rinse and wipe off again w a dis infective wipe . Usually a good condensate line flush and call it a day . Now when I look at selling mini splits I make sure they understand that if they want proper operation and longevity then proper maintenance of indoor and outdoor equipment is a priority and being on top of cleaning the filter at a mim of every month if not mini splits may not be for them . I don’t bother quoting jobs that are in need of a good house cleaning why cause they will never clean the house what would make them clean a filter ? Nothing and of course it’s highly doubtful they will want to pay for any service so I try to be way up front about maintenance and costs . It’s sad that they do not a better filter for them but it is what it is . I ve always been a either eac or high media filter guy on all my installs and for last 20 years always 2 pleated for roof tops ,there’s nothing worse then having to clean evaporators whether it’s a roof top unit on a curb or a air handler in a attic always some liability in ceiling tiles or Sheetrock all depends .the cleaning of these units are usually neglected mainly I feel due to being time consuming and expensive w liability from water or cleaning damage stains and that’s it really up to the contractor to inform the customer about all cost up front including future maintaince . In closing I see more of the mold issues on multi head systems as opposed to single zone units . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • DJDrew
    DJDrew Member Posts: 84
    edited June 2020
    Cleaning and Maintenance....this has been my biggest complaint with the mini-split system we had installed (4 head system; three upstairs in bedrooms, one downstairs.)

    We had 5 companies come in and give us quotes for adding AC. Three companies recommended the mini-splits, one a space pack solution and the other was a traditional system installed from the attic down. All 5 talked about the benefits of the mini-split, two gave some reasons why they were proposing a different solution. None of the companies warned about the cost of regular maintenance and the cost of deep cleaning the mini-split units.

    We keep our house fairly clean - especially since our kids love touching everything and then sticking fingers in their mouth, so it's a fairly clean house. I clean the filters in our mini-splits monthly and still experience clogged condensate pumps from time to time. And while cleaning the condensate pumps, it's easy to then notice the caked on dust in other parts... meaning it's time to call a pro in to deep clean.

    If I had to do over again, I would probably not go with a minisplit solution unless cleaning was made much more easy.

    The other issue I have noticed with the minisplit system is that the air in the house gets fairly "stale" after a day or two of running the system and the windows closed. From talking to a few people, I am being advised to install an ERV and to duct fresh air vents into the bedrooms. Going with all that hassle of ducted vents and an ERV unit, I probably should have just installed a mini-ducted system that could have had an ERV tied in directly.
  • bio_guy
    bio_guy Member Posts: 87
    edited September 2020
    This is the biggest drawback for me. I have seven high wall units that were installed when gas prices were still favorable to heat pumps. i kept the furnace and went back to gas heating. At least yearly, I take off the main cover and louvers, remove the drip pan , crack open the coils on the left side and remove the blower wheel. That all goes out to the driveway to be hosed off, soaked in a tub with dish detergent and scrubed with a big soft gong brush or toothbrushes and cotton swabs. Finally it all gets dipped (10 minutes) in bleach solution. Usually I dry it all in the sun.

    Inside, the bib goes on after brushing crevices with a toothbrush and evaporator cleaner. I then take my trusty tank sprayer and hose it all with an evap cleaner. If the coils have any residue, foam cleaner. I rinse and finish it of with an EPA fungicide HVAC cleaner. Then it all goes back together.

    This takes way too much time. The blower wheel is the biggest problem. If you don't take it out and clean it and around it, a lot gets left behind. The goop comes off pretty easily with a strong hose and detergent and brush.

    The wheel gets gunked-up for the same reason, I think, that plastic fan blades get dirty on the leading edge. Think about how box fan and ceiling fan blades often look. Static charge builds up as they rotate through the air. Small charged particles that zip through the filters and the coils get caught (by this efficient rotating electrostatic air cleaner.) If someone could figure out a practical way to continuously neutralize the static charge on the blower blades, or catch the charged particles before they get into the unit, it would save me a lot of grief. Note that this is a recently-developed hypothesis.

    P.S., I started using pan tabs too. It is easy and it keeps, at least, the drip tray clear. I put them on the coils where condensate drains both on the top and bottom coils. It is easy to monitor with filter cleaning. I've been watching for any effect on the aluminum. So far, after at least three years, no effect beyond discoloration that might be expected from coating that little bit of the coils with the stuff, no corrosion.
  • motoguy128
    motoguy128 Member Posts: 394
    edited September 2020
    The blower wheel buildup is actually from air in the room being drawn into the blower at the outlet.  Not air coming through the coil.  

     I have customers that clean the filters religiously and the coil looks totally clean, yet blower is packed.  

    Bag works well for cleaning.   But still tedious and messy.  I find it takes a good 3 gallons to clean it well.  Run blower on low speed while spraying at different angles.  
  • SuperTech
    SuperTech Member Posts: 2,021
    I like the idea of running the blower at low speed to help fling the crap off during cleaning.  I'm usually trying to spin the wheel manually to achieve the same thing.
    My boss would never go for the process outlined by @bio_guy. I'm sure its the best way to clean them,  but the time involved would make it way too expensive for the customers. 
  • Motorapido
    Motorapido Member Posts: 307
    Does the same cleaning process apply to ceiling cassettes? I have a Mitsubishi mini-split with a ceiling cassette in three bedrooms. System is three years old. I clean the filters regularly but have not used foam cleaner on the coil. I have read about a plastic bag system that you hang from the cassette so you can spray the foam cleaner. I do pretty much all mechanical work myself and have not had the installer come back to do a cleaning. Seems like other than potential mess, it should be easy. Anybody have tips on cleaning a ceiling cassette mini split system?
  • ChrisJ
    ChrisJ Member Posts: 15,154
    edited September 2020

    The blower wheel buildup is actually from air in the room being drawn into the blower at the outlet.  Not air coming through the coil.  

     I have customers that clean the filters religiously and the coil looks totally clean, yet blower is packed.  

    Bag works well for cleaning.   But still tedious and messy.  I find it takes a good 3 gallons to clean it well.  Run blower on low speed while spraying at different angles.  
    It could also be the fine dust is more likely to stick to the static charged plastic than the metal evaporator.

    I'm not impressed by the "filter" used on minisplits. Highly disappointed, actually. Does it catch a lot of dust, sure, but it's by no means a MERV 8.

    I'd be very cautious with any UV light, especially one strong enough to actually kill things due to all of the plastic in a mini split head regardless of what is claimed.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • bio_guy
    bio_guy Member Posts: 87
    The reason that I take out the wheel is two-fold. I suspect that there is a little period, lag time, when the blades are relatively clean and not much sticks to them so I figure that getting them like new buys me some time. I have no data to support that so feel free to throw stick and stones as well as jeer in my general direction. I could even have it backwards, naked bladed foul quickly and then slow down.

    Second, there are crannies in in the housing that I can get to a lot easier with the wheel out. Yup, it takes a lot of time…. times seven. I could certainly not afford to pay a technical pro to do that although a two-person team with a minimum wage helper might be able to pull off a good price. A garden hose with a old-fashioned pistol-grip sprayer and the brush gets them looking like new. Spraying at different angles helps as motorguy indicated and so does the brush. Brushing it dry does ont work well.

    The problem with the bag, as I use it, is that it blocks assess when it is in place. I can’t reach in there very well. Something more open in front would work better , but let more aerosols out into the room. I’m kinda moving toward some kind of trough on the floor with something just under and between the unit and wall to catch the drips/flow going that way directing them into the trough.

    Motorguy, have you seen any data or have any specific observations that eddy currents are carrying in dust? I admit that it seem unlikely for so much junk to get through the coils (but see below), but so does the eddy current.

    Looks and intent can be cryptic sometimes. How can a filter that is intended to catch coil clogging material let so much through? I’ll attach a pick of a filter designed to let through stuff that won’t get caught in the free-air condensing coils for two of our cascade ultra low temperature freezers (-86C) at work (Pannasonic nee. Sanyo). Apparently this is done to cut down on filter cleaning. Our other units in the same location with more conventional filters get crapped up relatively quickly. The pictured ones, I clean whether they need it or not.

    Here is something else that I picked up recently that is related. True Mfg (kitchen coolers, merchandizers,…. now has their condenser blowers start up in the reverse direction to blow off accumulated dust every cycle. After a brief reverse flow, they turn around. (Yea, I know you can’t do this with a squirrel cage.)

    Yes, if the UV is strong enough to be effective, It will break down any plastic that is not formulated to resist it.

  • momoncall46
    momoncall46 Member Posts: 2
    I had no idea how labor intensive and expensive cleaning the indoor mini-split wall unit would be. I found my unit with a heavily soiled blower fan after experiencing a foul odor each time I turned the unit on. (Only used for two summer seasons in NY) That would be the equivalent of eight months. Thankfully my son has a good understanding of the units, He did his own home. He took the blower fan out and I cleaned it in the tub with a brush and soapy water and high powered sprayer attachment. He cleaned what he could reach on the wall unit. Now I purchased a room air purifier . I am a clean freak. I am always cleaning . After only about 6 weeks, maybe not even, the dust buildup on the blower fan has begun. This is so ridiculous . Something has to be improved in the design of these units. If I knew then , what I know now, I would have never chosen a mini-split unit for cooling. End Rant !!
  • momoncall46
    momoncall46 Member Posts: 2
    To add: The other thing that puzzles me is the screen filters never really seem to be dirty. Despite what they look like I do remove them regularly and clean and dry them. Why/How does this much dust get past those filters and dirty the blower fan. That's why I bought the air purifier, a good one. I don't turn it off. It does not make a difference, the blower fan is already dirty.
  • pecmsg
    pecmsg Member Posts: 4,385
    Oversized systems do not dehumidify well on the lower speeds this causes excessive moisture and mold to grow. 

  • SuperTech
    SuperTech Member Posts: 2,021
    To add: The other thing that puzzles me is the screen filters never really seem to be dirty. Despite what they look like I do remove them regularly and clean and dry them. Why/How does this much dust get past those filters and dirty the blower fan. That's why I bought the air purifier, a good one. I don't turn it off. It does not make a difference, the blower fan is already dirty.
    Yup. Like stated above it's not dust and dirt, it's biological growth.  Mildew maybe. This is a side effect of the way mini splits modulate fan speed and compressor output.  When they run on the lower speeds and lower output, like many oversized units will, the temperature of the coil and moisture in the unit make it a ideal environment for fuzzy black growth to accumulate on the blowers. I wouldn't want to deal with that in my home. I'll stick to ducted systems. 
    EBEBRATT-Ed Member Posts: 14,499
    You have to look at it the way a manufacturer or contractor would. If it's dirty you need to replace the equipment. LOL Planned obsolescence..
  • DJDrew
    DJDrew Member Posts: 84
    One item that I have found helped our case was to not let the fans run too slow when on cooling or dehumidifying mode. Keeping them on medium or medium-high seemed to allow more airflow over the blower wheel and unit, making it a little drier. Additionally, when we switch off cooling or dehumidifying mode, we run the fan mode on medium for awhile to really dry the unit out. 

    Those two extra steps, while not the most energy efficient, have significantly reduced the buildup of gunk on the blower wheels for us. (We still clean the filters monthly for good riddance.)