# How to keep AC from smelling?



## jtr1962 (Jul 27, 2005)

Now as everyone knows summer is my least favorite season by far but at least air conditioning makes it tolerable, even if I pretty much must remain a prisoner indoors from June through September. The main two problems with AC are that you alternate between freezing and sweating depending upon whether it's own or off, and eventually the air ends up smelly despite my best efforts. Of course I keep the filter clean regularly. In addition I've tried pouring bleach in the bottom of the unit, spraying the fins with disinfectant, scraping out as much of that greenish scum that accumulates on the bottom tray as I could, and also pulling the units out once a year to give them a thorough cleaning inside. None of this really works that well. When its humid, as it usually is, you get moisture on the condenser fins. This falls into the tray, and acts as an ideal environment for foul-smelling mildew. Keeping the unit running continuously helps, but this often means bucking the AC with a ceramic heater when the room starts to get too cold. Needless to say that wastes a lot of electricity. Letting the unit cycle, especially on economy mode where the fan shuts off when the compressor does, virtually guarantees that the air will stink for a good 20 minutes or more the next time it starts.

Has anyone found a solution to this besides joining Sigman in Alaska?

As an aside, with the current state of electronics it would be very cost effective to make units which simply "throttle down" the cooling power as the setpoint temperature is reached, instead of cycling on and off. This would mean nice, steady temperatures, and probably less smell since the unit might not be condensing much water when it's throttled down. I'd like to know why aren't air conditioners made this way. Cycling seems half-assed at best. It also strains the compressor. I'd certainly be willing to pay $50 more for a unit which runs only at the needed power to hold the room temperature.

P.S. I would definitely have a summer home in Alaska if I could afford it but let's keep this thread to affordable solutions.


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## mattheww50 (Jul 27, 2005)

1). In the off season, clean the drip pan completely and try painting the drip pan with an anti-fouling boat paint. Also make sure the drain line is clear. There should be very littler accumulating in the drop pan if the drain line is clear.

Also spray all condenser surfaces with Chlorox, and use a brush to clean as much of the surfaces as you can. Wait 10 minutes and then rinse. That will kill anything living on the coils, 

2) Run the unit in the heat cycle if it is heat pump to dry off the coils on a regular basis. That will raise the temp in the coils to about 140F or more. 

The trick is to make sure that the cooling coils are bone dry at regular intervals. Mold and Mildew don't tolerate being baked very well all.

That will prevent most things from growing in it. The other thing (which costs $$$'s) is to put an electronic air cleaner in the system. They generally go in front of the cooling coils, and will catch most particulates. They are basically electrostatic precipitators. That will result in many fewer bacteria and mold/mildew spores reaching the 'wet' part of the system where they can grown. I will tell you that cleaning the precipitator plates is no fun at all. 

Variable speed single phase electric motors are electronic 'messy', and the slower it runs, the less efficient it is.


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## James S (Jul 27, 2005)

sounds like you've got window AC units? You talk about pulling them out once a year so that sounds like a window unit rather than a central AC unit?

In either case, you need real coil cleaner and not just bleach. (plus bleach will eventually corrode the coils I think I read somewhere, so make sure you rinse it well) Find a plumbing or hvac supply house in your area and get a jar of real coil cleaner. This stuff is very acidic and dissolves everything. Don't get it on you or your furnishings! Bleach kills most living things, but with stuff like mold and mildew it won't reliably kill the spores and so as soon as the bleach evaporates the stuff starts growing again. Over on my favorite HVAC forum they call that cleaner "yellow death" But it will get rid of EVERYTHING in your coil. (remember to rinse completely after using!)

Lastly, I think you need to not leave it in economy mode. If the fan keeps running after the compressor has cycled off it will dry off the coils. If they just sit there wet then you already know what happens /ubbthreads/images/graemlins/icon15.gif

What would be ideal would be a unit that ran the blower on low just for 5 minutes after the compressor cycled. That would be enough. And make sure you're not pulling outdoor air through the coil at that point or it will just keep it wet and reseed it with nasties.

But really, I think starting with a really clean coil will make a huge difference. Even if you have to do that twice or three times during the cooling season you'll be better off than you are now.

EDIT: and as I sit here avoiding the trip I need to make into my own attic to take some readings from my slowing dying central AC unit I am thinking of other reasons that you might have standing water in the thing. Check the level of the mounting to make sure that the pan actually drains out the back. If the water is sitting in there cause it's tipping forward or something that would certainly cause it to grow an impressive aquaculture in the bottom /ubbthreads/images/graemlins/smile.gif


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## jtr1962 (Jul 27, 2005)

Yes, these are window AC units which were wall-mounted by myself. Basically, I cut a hole in the outside brick wall, a matching hole in the sheetrock inside, and screwed the case of the unit to the wall frame. The guts of the AC slide in and out for cleaning.

Now as for the water in the pan, these are newer units (purchased 1994 or later) which claim use the water to cool the hot side so as to gain a bit in EER. The units are mounted properly so that the water drips towards the outside. They also have a plug to keep the water from accumulating but I always left it in since I wanted the units to run at maximum efficiency (and cooling power).

I haven't been using economy mode this year to see if it helps. To some extent the problem is a little better but I can smell the difference right away once the compressor kicks off. Of course, on days when it's cool enough to turn the unit off I get that awful stink when I turn it on the next day even if I let the blower run a few minutes prior to turning it off.

I was going to try liberally spraying the fins with Clorox as suggested by mattheww50. Thanks for mentioning that it is corrosive. I might try the yellow death if I can find it in a local HVAC store.

No, I don't leave the vents open so no worries about reseeding the fins. The outside air usually smells horrible this time of year anyway so why bring it in? Today it smelled like an open sewer outside. Literally.

This thread reminds me that the units probably need a midseason cleaning anyway as they've been doing extra duty with all this extra hot weather. The Kill-A-Watt I have attached to my bedroom AC says 580 kW-hr and 1128 hours (47 days) so far this season. At $0.18 per kW-hr that's $104.40 just to cool my bedroom for less than 2 months.


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## AJ_Dual (Jul 27, 2005)

Is there any practical way you could cram a UV light source in there that's wired to be on when the coils are running?


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## James S (Jul 27, 2005)

i've always been skeptical of UV light in an AC unit. Some people swear by it, but it can really only kill what it shines on for an extended period of time, and there is no way that it will shine through every fin and nook and cranny of the coil. So the side of the coil facing the light might not accumulate mildew but what about the back of it and in the middle?

you might be able to use something like that to keep stuff from growing in the pan if you could mount it down there though.

Might be more interesting to get a can of teflon lubricant or a can of scotchgard with Microban and clean the coils and pan and then spray them with that. I wonder if that would keep the buggies from being able to stick and grow... I have no idea what that stuff would do to your coils. But since they don't heat, only cool there shouldn't be aby problem with the teflon out gassing into the room as that only happens at high temperature.


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## KC2IXE (Jul 27, 2005)

Can't resist - did you try plugging the HVAC's nose?


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## Lynx_Arc (Jul 27, 2005)

I had a unit that was doing stuff like that and I found out it later when they get a little low on freon instead of the humidity dripping off in the pan easily more of it stays on the coils. When I had it serviced I had no more problems as now the water drips off in the pan instead of building up now and then on the coils.


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## Sub_Umbra (Jul 27, 2005)

I don't have an answer but if I were in the same situation I would take it very seriously. *Legionella* loves ac coils and it has been around for a very long time. The bug was only named after a particularly virulent strain killed a few with what became known as *Legionaire's Disease* at a convention. It's all about ac. Any place where there is a mist or dripping water.

Living in SE Louisiana it scares the poo out of me.


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## ChopperCFI (Jul 28, 2005)

I have used a refrigeration disinfectant called BG Frigi-Fresh in my car AC and it works great. Should also work on bigger coils. BG Products also makes a foaming cleaner called Frigi-Clean for just such situations, but I haven't had the need to try it.

It's hard to find, but I have had luck getting it at a local HVAC repair company in town and most recently at a local auto repair place. On the web I have seen it vary in price from $6/can to $23/can. Here is one of the cheaper places.


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## cy (Jul 28, 2005)

I'd remove plug and allow unit to drain properly. 

are you sure mfg recommends allowing moisture to accumulate? how would this improve effeciency? heat is being removed from exchange coils to rear coils for dispursal.

could be wrong, but don't think standing water improves operation.


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## Lynx_Arc (Jul 28, 2005)

Some window units have a slinger which picks up water from a drip tray and throws it up in the air stream blowing out of the coil to help increase cooling by evaporation. There is a built in level limit where the drain is allowing a certain level of water to be in the tray available to by picked up by the slinger and thrown into the rear fan/coil area. At times though the water pathways can get blocked either allowing higher than normal levels of water in some areas or even overflowing. I would guess more of the mold issue is not in the pool of standing water but in the areas on the front coil and the air ductway in front. This can be caused by running the unit when it is raining out, slightly low levels of freon causing slight freezing/buildup of water on the front coil and dirt buildup catching water in areas giving a place for mold and mildew to thrive.


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## HWilliam (Jul 28, 2005)

[ QUOTE ]
They also have a plug to keep the water from accumulating but I always left it in since I wanted the units to run at maximum efficiency (and cooling power).

[/ QUOTE ] 

That doesn't sound like a good trade-off considering the time, effort, and money expended by you to keep killing the crud that's growing.

I'd pull that plug, do a very complete cleaning, and then see what happens.


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## goldenlight (Jul 31, 2005)

How strange you have so much trouble with window type AC units. I've owned at least 8 or 10 window AC units over the past 30 years, (I use 2-3 at a time, now) and I've _never_ had a problem with odor from any of them.

Sometimes in my car the AC will smell for the first few minutes it runs; especially if I ran it for a few days, and then didn't have to use it for a few days. But it clears up pretty quickly.

And yes, it gets _very_ humid here. Dewpoint hit 80F last week(!)

Sorry that I can't help; (but others have made very sensible suggestions) maybe I've just been lucky!? /ubbthreads/images/graemlins/ooo.gif


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