sealing air leaks in indoor AC unit

masraum · 09-14-2009, 12:12 PM

I've got a normal 2 part AC unit. Outside is the compressor/condenser and inside is the furnace, evaporator and fan. We had the evaporator replaced a year or two ago. I was up in the attic the other day and noticed that there are a few places in the housing where cold air is being blown out. The goop that's currently sealing most of it is like a cross between bondo and flour/water. It's a plasticy white goop. I'd like to properly seal the unit. What's the best way to do that/best stuff to use?

I noticed because I am tinkering with some weather software. I put temp sensors in the house, attic, and outside and noticed that when the weather is just right, the temp in the attic can actually be lower than inside the house and outside.

I'd like to minimize how much I cool the attic.

lowyder993s · lowyder993s's Garage

I sell this stuff DP1010...about 10k gal/yr...send me an addy...I'll send you one:

http://www.designpoly.com/sealants.htm

masraum · 09-14-2009, 12:37 PM

Wow, thanks!

PM sent

Neilk · 09-14-2009, 02:35 PM

I had the same issue and just called our contractor who installed our AC unit. He was willing to come back 2 years later and fix it. I might hit Jim up for some of his "goop" next year if it leaks again.

Neil

idontknow · 09-14-2009, 07:45 PM

Is the duct board box breaking loose from the A/C unit? You're going to have to resupport and strap it. If you have leaking around where the flex collars link to the solid box. The inner flex hose has popped off and needs to be reattached and strapped. Then reseal the outer connection.

More precise instructions are available of course, but where is the leak coming from?

masraum · 09-14-2009, 08:06 PM

I'll see if I can get up and look at things and maybe take a couple of pics. Thanks

T77911S · 09-15-2009, 08:55 AM

same problem. when i bought my house, the attic was cooler than my house. clean the duct board, retape, and cover it very well with mastic, that goopy stuff you were talking about, or the stuff the guy above offered.

masraum · 09-20-2009, 09:57 PM

OK, the red arrows point to where I feel the leaks. I've got air that comes out of the vent pipe (we had the pipe capped a long time ago, and when capped, we heard gurgling noises coming from one of the upstairs bathtub drains. Uncapping the vent stopped the noise), some comes from where the insulated drain pipe comes out of the drain pan, and a ton can be felt when I stick my hand under the unit (can't tell exactly where the air is coming from, just feel it. sealing under is more of a pain so he did a crappy job?).

So, what is this "taping" of which you speak? I don't see any tape. My unit seems to be internally insulated sheet metal boxes that are screwed together and then gooped. I don't see any tape anywhere.

sammyg2 · 09-21-2009, 10:43 AM

If the systyem is leaknig cold air into the attic, it's also sucking hot air into the house to replace it. It creates a low pressure zone in the house so any drafts or leaks will be exaggerated. That makes the system even less efficient.

I had the same problem a couple months ago and I solved it with aluminum duct tape. The goop would probably last longer but my hands were still clean.

masraum · 09-21-2009, 03:47 PM

Jim, I got the goop today, thanks tons!

idontknow · 06:11 PM

The pressurized drain line is most likely from a lack of a drain line trap. A simple U trap should work to keep the air from blowing out but the water flowing.

I see you have a sort of access panel on the duct box, what does that connect? The one side is the evaporator coil pack is all I can tell. Next time up, buy some foil tape and open the access door. Have a peek around looking for gaps. If you shine the flashlight on the outside while looking in it should show you any cracks. Make sure the area is cleanish and use the foil tape to fill in all cracks and openings. Then coat the whole area as best you can with the goop. Goop the area inside and out.

To help seal the area around where the drain line connects to the coil pack, find one of those swimming noodles?. Piece, cut and fit it so it creates a larger sealing area around the box. Electrical tape holds the sliced parts together and goop it all lightly but completely.

Swimming noodle is a soft foam hollow noodle about 2.5" round and 5' long. Kmart and Walmart have em in the pool section.

idontknow · 09-21-2009, 06:24 PM

Oh yeah, foil tape. Available at most hardware stores.
from: http://www.fastenal.com/web/products/detail.ex?sku=0454132&ucst=t

masraum · 09-21-2009, 08:46 PM

Quote:

Originally Posted by idontknow

The pressurized drain line is most likely from a lack of a drain line trap. A simple U trap should work to keep the air from blowing out but the water flowing.

I see you have a sort of access panel on the duct box, what does that connect? The one side is the evaporator coil pack is all I can tell. Next time up, buy some foil tape and open the access door. Have a peek around looking for gaps. If you shine the flashlight on the outside while looking in it should show you any cracks. Make sure the area is cleanish and use the foil tape to fill in all cracks and openings. Then coat the whole area as best you can with the goop. Goop the area inside and out.

To help seal the area around where the drain line connects to the coil pack, find one of those swimming noodles?. Piece, cut and fit it so it creates a larger sealing area around the box. Electrical tape holds the sliced parts together and goop it all lightly but completely.

Swimming noodle is a soft foam hollow noodle about 2.5" round and 5' long. Kmart and Walmart have em in the pool section.

Good to know about the U-trap, thanks.

If by access panel, you are talking about the screwed on piece of sheet metal in the middle of the picture. It allows visual inspection of the fan side of the coils (dirty, dust, ice, etc...)

yes, the left side of the picture is the box with the evaporator, the right hand side is the furnace/fan.

Thanks all for all of the info/advice. I'll get up and look at it again this weekend.