Deposits on room a/c louvers and condensate (long)

[wkilleffer]

Hello everyone,
My question is about a room a/c unit (window unit) that we have mounted through a hole in the wall of our bedroom.
The unit's a Kenmore, and I can provide more specific detail as to model numbers if needed. During the hotter months, we run it all night most nights. We rarely use the power saver mode as it doesn't cool very well. It's at least five years old and maybe as much as eight. My grandparents had it installed back when they owned the house and lived in it.
I've always been careful about keeping the filter clean, but the interim owners of the house might not have been. I vacuumed the coils as best I could with the brush attachment from my vacuum cleaner.
My first question involves the air movement louvers. Recently, I've noticed a dark brown residue of some sort on them. I can wipe it off with a moist paper towel, but it comes back again over time. It's almost like dirt is getting through the filter and getting blown out with internal moisture. Not impossible, considering the filters on these newer a/c's are borderline rubbish for anything smaller than a human hair, but I digress...
What is causing that to happen, and is it cause for concern?
Also, I've heard that modern room a/c's don't drain out all of their condensate the way older units do. Why not? This seems like a terrible idea, like an invitation to bacterial growth, maybe even Legionnaire's Disease.
Thank you,

William Killeffer
East Ridge, TN

[LazyPup]

From the diagnostic information you provided, 5 - 8yrs old, not cooling well on "power saver mode" and a residue on the discharge louvers, i would guess that the Evaporator coil needs cleaning.

You may have noted that in another thread I stated that cleaning an evaporator coil is best left to a trained professional, however window AC units fall into a whole different category.

First of all, it is nearly impossible to find a HVAC tech that is willing to work on window units simply because in most cases the cost of parts and labor would exceed the value of the machine.

Cleaning coils is a relatively easy task, but in the case of central AC it requires removing access panels and working in a confined area with rather fragile capillary tubes, soft copper refrigerant lines and exposed 220v electrical circuits. That should best be left to a trained technician, however the evaporator coil on a window unit is immediately accessible by just removing the front cover and pulling the filter medium off. All the controls, electrical circuits and refrigerant lines remain well protected inside the cabinet.

Window unit evaporator coils can be cleaned with the unit in the window but it is best to take them outside to prevent creating a mess in the house. (If you do elect to clean it in place be sure to place a fairly large plastic drop cloth on the floor in front of the unit before proceeding.)

In the trade we use a concentrated foaming coil cleaner concentrate which comes in a gallon container. Four ounces of liquid is mixed with a gallon of water in a tank sprayer to make a working solution. Although it is not real expensive obviously a gallon of concentrate would be far more than what a homeowner would need, not to mention the cost of purchasing a tank sprayer dedictated to this job. Fortunately if you will go to an HVAC or Applinace parts supply house they carry 12 or 16 oz aerosol cans of foaming coil cleaner that is ready to go.
One can should be sufficient to clean both the evaporator (inside coil) and the condenser (outside coil) on a typical window AC.

TIP: While at the parts house ask them for a sheet filter for your machine. They have stock roll filter material than is simply cut to size with a pair of scissors.

To clean the coil,

1.Pull the electrical plug.
2. Remove the front cover and the filter medium to expose the front of the coil.
3. Lay out a drop cloth under the machine.
4. Shake the aerosol can vigorously to mix the cleaner.
5. Spray the cleaner directly into the coil. (The aerosol will come out in a fine stream similar to that of a WD-40 can.) Begin at one corner and work across the coil, dropping down a bit an repeat until you have saturated the whole coil. The liquid cleaner will begin to expand creating a foam that looks like shaving cream. As the foam expands it literally pushes the dirt out of the fins. The foam tends to get warm as it cleans and you may see faint wisps of vapor that look like smoke, Do not be alarmed, that is normal. In about 30 to 45 minutes the foam will break down to a liquid again. Although the instructions on the cans often say no rinse is necessary, i personally prefer to rinse the coil by misting heavily with a hand aerosol bottle filled with plane water. Keep a close eye on the condensate tray under the bottom of the coil. If it is filling and doesn't seem to be draining you may need to clean the drain tube by inserting a stiff wire from the outside back drain port.

Now repeat the process on the condenser coil on the back side of the unit.

For larger window units that slide out of the cabinet I prefer to take them outside to do the cleaning. Wrap the fan motor with a plastic bag and tape it in place, then you can carefully use a garden hose to rinse them out. Be careful not to use excessive water pressure that could bend the fins.

After it is rinsed out, allow it to remain in the sun a while to insure that it has dried thoroughly before returning it to the window.

Here is a little trick i devised some years ago to insure the machine is thoroughly dry. Take an old jar lid, such as a mayonase jar lid, and lay it on top of the machine. Fill the lid about 1/2 full of water, then wait till the water in the lid has evaporated before returning the machine to the window. The idea here is, if it has had adequate time to evaporate the water in the lid, we can then assume any residual water than may have got into the control section or motor housing should have evaported at the same rate.

In regard to condensate drain pans not draining well. This is not a new concept. Many window units have a ring around the outer circumferance of the condenser fan, which is technically called the "Slinger Ring). In normal operation the bottom edge of the fan passes through the condensate pan and picks up water which is the slung into the condenser coil. The evaporation of that water off the condenser coil actually increases the efficiency of the machine.

You are correct that bacteria can breed in condensate pans and create a slimy biofilm which has be linked to legionairse disease. To prevent the formation of biofilm you can periodically pour a half ounce or so of ordinary household laundry bleach into the pan to sanitize it or while at the HVAC parts house you can get a small pack of "PAN TABS". Pan tabs are a slow release choline product in tablet form that is made specifically for HVAC condensate trays. They are very inexpensive and can be used in both window AC and Central AC evaporator units.

[wkilleffer]

Thanks for your reply, lazypup.
Do I need to worry about the coil cleaner eating away anything inside of the a/c case? Someone told me that stuff can be harmful to styrofoam or any other plastic that might be part of the a/c case.
I'll go ahead and get some cleaner. At least I could go ahead and clean the outside.
Thanks again for your suggestions.

William Killeffer
East Ridge, TN

[HayZee518]

Most modern A/C units don't drain the condensate outside anymore - I used to see water dripping out the pan all the time. Nowadays there's a slinger on the condensate fan that blows the water through the condensate coils in a mist.

[LazyPup]

If you are careful to only spray the cleaner into the evaporator coil there should be no problem at all. The air flow is ducted from the back of the evaporator coil to the discharge vents and there is minimal contact between the air and any insulating materials inside the unit.