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#4782535 - 06/09/18 08:44 PM HVAC Coil Cleaning
sleddriver Offline


Registered: 02/06/10
Posts: 4611
Loc: Central Texas
My yearly ritual. Close neighbor's contractor generated lots of limestone dust & mortar mix that wafted over where the outside unit was located. Sprayed down outside coil with a whole can of TuffStuff. Next I sprayed the indoor A-frame coil, letting both soak while I went to purchase new 3M filters. Too bad Lowe's no longer sells these better quality filters in a single. Now have to buy two bundled together. I prefer 3M filters because their pressure drop is quite a bit lower than Purolator's equivalent filter.

Got back and used a pump up sprayer to rinse both coils with soft water. Outdoors, I prefer to borrow neighbors pressure washer + wide-fan-tip and backflush the coil. Unfortunately he was unreachable today, it rained 0.3" and now outdoor humidity is 100%.

Removed outer cover on evap. coil and rinsed it from the clean (downstream) side. There was quite a bit of "very fine" dirt. As the coil sweats, this fine dirt turns to mud and will remain in place until this cleaning treatment. Post rinse, the drip tray had lots of this dissolved mud. So I flushed it out from both furthest ends back towards the drain until it was gone.

Upon installation of both new filters, I noticed something very odd. The Air Flow indication arrow appeared to be backwards. Didn't make sense. I'll call 3M Monday. Given the poor fit though, I used some UL-181B/X metal foil tape to seal in both filters preventing air from sneaking around the perimeter.

Buttoned it all up. Indoor air temp had risen to 82°F over several hours. Humidity was probably 42% or so. I set the t-stat to 75F and restarted. Indoors is now 76F and indoor humidity has dropped to 37%. Quite a shock as outdoors it's 78F, dew point is 77F, which means outdoor humidity = 99%. So air flow across the clean evap coil is good, it is cold and sweating, thus indoor humidity has quickly dropped since the restart.

I always notice this drop in indoor humidity after cleaning the evap coil. Before, indoor humidity would be around 41% with t-stat set @ 78F. In humid Cen. Tx., humidity removal (latent heat) is just as important as cooling air (sensible heat).

Very surprised by the rain today. Didn't see it in the forecast. Weather-babe blew it.
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#4782705 - 06/10/18 03:19 AM Re: HVAC Coil Cleaning [Re: sleddriver]
Marco620 Offline


Registered: 02/25/14
Posts: 2195
Loc: Deplorable Kansan,HK fan!
I go to Home Depot. They sell a spray yhats is citrus based to help
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#4782752 - 06/10/18 06:04 AM Re: HVAC Coil Cleaning [Re: sleddriver]
CourierDriver Offline


Registered: 12/27/09
Posts: 4958
Loc: Tn.
Cleaning the coils is a good thing as heat transfer is important as the freon changes back and forth from a gas to a liquid. Also, clean your blower motor fan blades at your evaporator. If they have dirt on them which most do, your efficiency can go down about 15 percent/cfm. They are not always easy to get to...good luck. Youtube should a video on this..

If you want to, you can install an electronic return air filter grille system where your return air filter is located if you want to spend the money...no more filters to buy, just wash out the electric grille when it gets dirty..
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#4782774 - 06/10/18 06:52 AM Re: HVAC Coil Cleaning [Re: sleddriver]
billt460 Offline


Registered: 03/30/15
Posts: 4417
Loc: Glendale, Arizona
I clean my coils at the spring start up of my unit every year. Out here in Arizona it gets very dusty, and if you don't clean them, your coils can lose a great deal of heat transfer efficiency. But I don't use a pressure washer to do it. Just a garden hose at city pressure, and a good nozzle. A pressure washer can easily bend the very thin Aluminum metal used in the coil construction.

First I soak the coils as much as possible with Simple Green straight from the bottle. I then immediately spray from both directions top to bottom. And you wouldn't believe how much dirt gets washed out. After I'm finished, I immediately start the unit, and let it run for a good half hour to dry it out completely.

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#4782783 - 06/10/18 07:10 AM Re: HVAC Coil Cleaning [Re: sleddriver]
TWG1572 Offline


Registered: 12/18/07
Posts: 559
Loc: Madison, Wisconsin
This is a good reminder thread. I used your thread from last year as a motivation to start cleaning my A frame coil. Lots of nasties, so much that I ended up plugging my drain line. It was a cobbled up affair made of 3/8 rubber hose that the prior owner installed, so I ended up installing a proper PVC drain with traps and cleanouts.

My only frustration is I can't ever seem to get my humidity down below 45, regardless of temp. I have no idea why that is.

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#4782796 - 06/10/18 07:36 AM Re: HVAC Coil Cleaning [Re: sleddriver]
Kestas Offline



Registered: 06/04/02
Posts: 12345
Loc: The Motor City
Are you talking about a dew point of 45°? I don't think you can get much lower without running the risk of icing over the evaporator coils.

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#4782799 - 06/10/18 07:42 AM Re: HVAC Coil Cleaning [Re: sleddriver]
Linctex Offline


Registered: 12/31/16
Posts: 6178
Loc: Waco, TX


Yep did all mine three weeks ago - pretty much same procedure you described.

Originally Posted By: sleddriver

Upon installation of both new filters, I noticed something very odd. The Air Flow indication arrow appeared to be backwards. Didn't make sense. I'll call 3M Monday.


Me too....... 3M "Filtrete"... correct?

I followed the flow arrow....It sure looks like it's in backwards to me, too.
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#4782801 - 06/10/18 07:43 AM Re: HVAC Coil Cleaning [Re: TWG1572]
Linctex Offline


Registered: 12/31/16
Posts: 6178
Loc: Waco, TX
Originally Posted By: TWG1572


My only frustration is I can't ever seem to get my humidity down below 45, regardless of temp. I have no idea why that is.


It might not be healthy to live in an environment that dry.
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(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

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#4782804 - 06/10/18 07:49 AM Re: HVAC Coil Cleaning [Re: sleddriver]
Mr Nice Offline


Registered: 09/12/04
Posts: 21209
Loc: Orlando, FL
I need to start cleaning my A/C coils.

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#4782809 - 06/10/18 07:56 AM Re: HVAC Coil Cleaning [Re: Kestas]
TWG1572 Offline


Registered: 12/18/07
Posts: 559
Loc: Madison, Wisconsin
Originally Posted By: Kestas
Are you talking about a dew point of 45°? I don't think you can get much lower without running the risk of icing over the evaporator coils.


No - I was talking relative humidity. Sorry about being unclear. It seems to be in the "acceptable" range, but the air can feel a bit muggy in the house at times. I see Sleddriver reporting humidity levels in the high 30's and wonder if I could do something to get mine lower. It's probably not going to happen though.



Edited by TWG1572 (06/10/18 07:57 AM)

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#4782820 - 06/10/18 08:09 AM Re: HVAC Coil Cleaning [Re: Linctex]
billt460 Offline


Registered: 03/30/15
Posts: 4417
Loc: Glendale, Arizona
Originally Posted By: Linctex
Originally Posted By: TWG1572


My only frustration is I can't ever seem to get my humidity down below 45, regardless of temp. I have no idea why that is.


It might not be healthy to live in an environment that dry.


My indoor humidity was 18% yesterday.

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#4782838 - 06/10/18 08:21 AM Re: HVAC Coil Cleaning [Re: sleddriver]
Audios Offline


Registered: 11/19/11
Posts: 889
Loc: Lyndhurst NJ
I was up in my crawl space attempting to clean the evap coils and fan, but my unit is nearly 25 years old so i need to remove the whole case on the unit to access the blower. Its a York, I couldnt find any access points to just clean the coils and fan. The AC is pretty good, however on 90 plus days it struggles a bit to keep the house at 75. Is that typical? No access points at the evaporator?
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#4782872 - 06/10/18 08:54 AM Re: HVAC Coil Cleaning [Re: TWG1572]
emmett442 Offline


Registered: 12/07/16
Posts: 177
Loc: Wisconsin
Originally Posted By: TWG1572
Originally Posted By: Kestas
Are you talking about a dew point of 45°? I don't think you can get much lower without running the risk of icing over the evaporator coils.


No - I was talking relative humidity. Sorry about being unclear. It seems to be in the "acceptable" range, but the air can feel a bit muggy in the house at times. I see Sleddriver reporting humidity levels in the high 30's and wonder if I could do something to get mine lower. It's probably not going to happen though.



Blower speed has a big impact on humidity. The blower speed needs to be fast enough to provide adequate airflow to cool the house and prevent the evaporator from icing, but it has to be slow enough that the moisture has enough time to condense and run off the evaporator.

It's my experience that most systems are set up with the cooling blower speed too high. Cools the house just fine, but doesn't dehumidify well at all.

Blower cfm should be about 350 per ton. So if you have a 2 ton AC unit, set the blower speed close to 700cfm. There should be a blower perfromance chart somewhere in/on the furnace.
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#4782877 - 06/10/18 08:58 AM Re: HVAC Coil Cleaning [Re: sleddriver]
DBMaster Online   content


Registered: 09/18/12
Posts: 5323
Loc: DFW
I use pleated MERV8 filters sealed into the filter grills with foam weatherstripping. I clean the condenser coil annually, but previous checks of the evaporator revealed it to be very clean. I had to cut a "hatch" into my transition with tin snips to access it. I may check it again before the real heat kicks in, but filtration and sealing leaks around the filter housings will keep your evaporator very clean.

I do run my blower continuously which, as Sleddriver has pointed out in the past, does increase indoor humidity. I like the constant air movement and reduced dust. I replaced the blower motor in my unit two years ago. It was twenty years old at the time. Since I work for Lennox I got the motor and capacitor just above cost so it was a cheap fix. I noticed no real change in my electric bill when switching to continuous blower use.

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#4782880 - 06/10/18 09:10 AM Re: HVAC Coil Cleaning [Re: emmett442]
billt460 Offline


Registered: 03/30/15
Posts: 4417
Loc: Glendale, Arizona
Originally Posted By: emmett442
Blower speed has a big impact on humidity. The blower speed needs to be fast enough to provide adequate airflow to cool the house and prevent the evaporator from icing, but it has to be slow enough that the moisture has enough time to condense and run off the evaporator.

It's my experience that most systems are set up with the cooling blower speed too high. Cools the house just fine, but doesn't dehumidify well at all.

Blower cfm should be about 350 per ton. So if you have a 2 ton AC unit, set the blower speed close to 700cfm. There should be a blower perfromance chart somewhere in/on the furnace.


This is a good point, and not something I've heard discussed before.

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