We've got an attic AC unit. Over the past week the AC has shut down
(wonderful in our 90+ summer weather). It's doing this because of a
kill switch in the drip pan. As the drip pan fills up, it raises a
float on the switch and shuts the unit off.
By literally bailing the water out of the drip pan, we can get the AC
restarted. Of course this is not a practical solution.
line being clogged? Can someone walk me through some steps to unclog
The system has two PVC pipes coming out of the attic unit. One takes a
short bend and opens into the drip pan, this is the one thats seeing
the action at the moment. The other line seems to run towards the side
of the house, presumably to connect with the drain line off of the
bathroom in that direction. This line has an opening at a Y joint near
the AC unit. One part of the Y continues to the drain line as
mentioned above and the other part of the Y is a short piece of pipe
open to the attic. Thanks in advance for any suggestions.
after bailing system, add a gallon of 50% bleach/water to area that feeds
both lines with water, so that the bleach mix can kill the growth clogging
wait one hour
bail bleach out
apply compressed air to clogged line to clear, be careful not to get bleach
in eyes or on skin or breathe
wear goggles/ latex gloves/respirator
after line is clear, apply a 20% bleach solution once/month to keep lines
Shove something down the pipe until it is clear. Wire is good. A drain
snake may be OK but the tip may be too big. If that is the case, just cut
if off and run the flex portion down the tube. Most likely it is an
accumulation of dust the built up over time. Could be some slimey stuff
too, so once clear and flowing, pour a bleach solution in the pan and let it
How about going outside where the drain line dumps water and use a wet vac?
That will (hopefully) clear the drain. If it doesn't, leave the wet vac
attached to the line and go up into an attic and shake the drain lines.
Where I live they do not put floats in the pans.
Your air handler should have one drain going outside, directly from the
unit. The pan should have its drain going outside as well. Usually the air
handler drain is low on the outside wall and the overflow pan is high. They
do that so it will be noticed. The air handler should not be dumping into
A shop vac may be able to blow out the blockage. Other posters had good
suggestions on cleaning the pan.
I do not know why anyone would use both drain holes from a air handler. One
is enough. The manufactures supply usually 2 to cover all of the
If the house is new it might be time to call the contractor and have them
correct what sounds like an incorrect installation.
"Y" are not legal if they ever were where I live. Phoenix
The "Y" fitting you are talking about is probably a tee put there as an
air vent and/or a place to pour bleach into the line to help keep it
clean. You are probably going to have to cut the line after that fitting
to clear it out. First, try and find out where it actually goes. A lot
of units here are tied into a bathroom sink drain. Look at the drains on
your b/r sinks and see if one has a pipe hooked into it from the side,
coming out of the wall. If so, that is the a/c drain. Sometimes they
will clog bad enough that you have to dismantle the drain there and
clean it out. I've run into them before like that. Also a couple of my
co-workers have blown lines out from the attic and went down into the
bathroom to find black goop all over the walls and in one case the
ceiling. I agree that is usually better to have the secondary pan drain
hooked up and draining outside where it is visible, and even better
still to have both a drain and a float switch. Anyhow, good luck and get
back if any more questions about the problem. Larry
I'm amazed at the amount of water running through this thing. I guess
I just hadn't thought about it. We live in a very humid area and it's
been miserable so the AC is getting lots of work.
I don't think the main drain has an outlet outside the house. It runs
into some insulation after it leaves the handler but it appears to be
headed towards the bathroom and the drain pipe there.
I think I'll try to run some wire through it and remove the blockage.
I'd have to cut the end off of my snake to make it fit. I think the
opening in the main line is an access tube, maybe for this purpose?
Thanks for all the great suggestions.
It is not legal to run an AC condensate drain into a sewer. The only
thing that should tie into the sewer is plumbing fixture drain. The
drain of the unit should go outside. Cut it apart in the attic and use
a shop vac to suck out the main drain pan in the indoor unit. Then
suck the drain line that disappears into the insulation. With the AC
OFF so it doesn't make water for a while, go outside while the vacuum
is running and listen for the sucking noise. You will find where the
drain line comes outside. In the future you will be able to vacuum it
from there. It is usually next to the outdoor unit here, but sometimes
is put behind bushes to hide that ugly thing. :-)
You should not be working off the emergency drain pan. You can run a
drain line from the emergency pan to the soffit so you will know the
next time you have a problem before the AC shuts off or the ceiling
I used to work in a county that had no codes. As I recall, when gas lline
was run, the fire department came out to make sure it didn't leak.
Condensate drain? Anywhere.
Well north of you, in New England, the condensate from high efficency
boilers is routinely put into sewers and septic systems. In Colorado also,
as I recall. The difference there is that the acidic condensate has to be
Huh? Every AC unit I've ever seen (here in the upper midwest they're
typically in the basement) has the condensate line going to a floor drain,
which ends up in the sewer.
My mom's house has an attic AC unit which was installed in the mid 1970's.
It's condensate drains right into the vent stack. I have no idea if that
is/was legal but can't see how such a little trickle of water would cause
problems there. She was on a septic system until a municipal sewer was
finally installed a couple years ago.
Others have explained the primary and backup functions of the two
Most homeowners have no idea this is a critical maintenance item. Here
in SE Florida I hear all the time of severe damage to houses from
condensate leakage due to ignorance. Sometimes when visiting a neighbor
or friend, I'll point out the backup-pan pipe exiting their soffits, and
no one seems to know what it means when it drips.
Forget the advice about using chlorine. This is often repeated but is
based on more ignorance. The fact is it won't work for several reasons,
(1) the chlorine will only last perhaps a few weeks before decomposing
and/or flushing, (2) chlorine is inactive in the resulting high pH
condensate, (3) the chlorine demand to kill and dissolve a typical mold
clog is far more than you'll deliver this way.
A strong dose of hypochlorite may help the cleaning process because it
is so strongly alkaline, not from the chlorine. Lye drain cleaner would
work better, but I wouldn't recommend that either.
Polyquat tabs or pouches are also sold (or pushed by the repair trade)
as clog preventers, but I doubt these work for the same reasons, and
that the dose is tiny and short-lived.
In my experience, vacuuming won't usually work on a clogged condensate
pipe. On an easy clog, it will work a little, just enough to give the
illusion that it worked because the drain will flow again, just enough
for the condensate drip, but most of the clog is still there and will
quickly grow back.
The way that works is to install a disconnect at the air handler,
consisting of a PVC repair coupling or Fernco rubber coupler, and use a
rubber-tipped blow gun with 90 psi shop air to blow the clog(s) out.
This is a much more involved and expensive method, but it has always
worked for me. You get a hideos gooey clog splattered on the ground
where the pipe ends.
Make sure you have U-trap installed in the line. Otherwise air flows
through, collecting dust and fostering more mold growth that leads to
I just had a similar problem with our heat pump. I have two compressors
in the back yard, and one air handler in the attic and the other in the
We discovered a very wet ceiling in the basement of our 3-story
townhouse in MD.
Presuming a leaking water pipe, we called he plumber who had to knock a
hole in the ceiling about two feet by 18 inches. Looked around and
determined that it was NOT a leaking pipe but a leak from a pipe
associated with the air handler in the attic.
The heat pump guys came out and checked the attic air handler and
determined that it was a blocked drain pipe that handled the humidity
the air handler pulled out of the air. The water from the air handler
went down a plastic drain pipe. The guys who came out could not figure
out where that pipe led. They had a pistol-like device into which you
put a COs cartridge then fire it down the blocked drain.
They fired two of these down the drain then followed it with a gallon
or two of water. I stood in the basement ready to see if any water
dripped. None. Presume that's done the trick but we are going to leave
that ceiling unrepaired for a month or two to see if any more water
drips out. Servicemen also recommended pouring a bottle of the drain
cleaner formulated for plastic pipes down the "Y" joint at the head of
the drain pipe just an added insurance.
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