I'm ashamed to say, I haven't cleaned my a/c condensate drain line since we moved in (approximately 2 years ago - new construction). There are no blockages that I know of, but I need to clean it. I've seen differing things on the web about how to do this - 1 cup bleach, 1 cup vinegar, diluted bleach or vinegar, etc. I've even seen people install a ball valve between the T and the A/C unit, close it, and hook up a water hose to flush the line.

Can someone recommend the best way to clean? I have 2 a/c units in the attic. I believe both condensate drain lines come together somewhere under the insulation and drain to an upstairs bathroom (see attached picture). Drain lines on each unit look identical.

Questions:

1. Since there is no blockage, is the best way to clean with some chemical - bleach, vinegar, etc? If so, which one and what combination?

2. At the T fitting in the drain, should there be a cap? When the unit is blowing, cold air is escaping from the open pvc pipe. However, since this is plumbed directly to a drain, I've seen posts that say don't cap the T area or you'll get the gurgling noises at the sink with the drain.

3. Is it normal to have both condensate drain lines from different units combine into one drain?

Thank you in advance!

 

There is no "common" way to drain condensate. It's at the whim of the installer. Yes.... in your case... connecting both A/C units to one drain line is usual. I try to get the condensate out of the house. I'll usually follow the refrigerant lines with a drain line. That is not always possible.

I see a single unit in the picture. I don't see any trap in the main drain line. I see a stub up that should have a non glued cap on it. I see an overflow pan that SHOULD NOT be plumbed into the same drain line going down as the main drain.

It appears these units are above a finished area. There should be float switches in the overflow pans in case the main line backs up. You need to know when there is water in the overflow pan.... and more importantly before it overflows.

That rubber line below the sink is pretty much horizontal and is a great place for a clog to develop. Cleaning the lines before they are plugged is a good idea. That uncovered pipe is the place to pour in cleaners. Pour in one cup of bleach followed by some hot/warm water. The bleach will break up the algae and grease scum. Once a year is all it should take.

 

The units are perpendicular to each other. I couldn't get them in one picture. However, both units are plumbed the same way.

The main drain lines do not have traps. What is the purpose of that? Does it make a difference that the area under the sink is just above the sink trap? I was assuming that the builder is using that as the drain line trap as well. When plumbed to drain under a sink (above the sink trap) is there usually another trap near the a/c unit?

If I put non-glued caps on the stubs, is that going to cause the gurgling at the drain sink I thought I read somewhere?

The overflow pan is plumbed separately. It's behind the main drain. Bad picture on my part.

Good call on the safety switch. Going to look into that now.

Finally, under the sink - the black tubing is very stiff. Does it need to be this kind of hose? It seems like it would work a lot better if I could replace with a more flexible hose.

Thank you for taking the time! I appreciate it.

 

Where does it drain to ?

The trap at the air handler keeps the cold air from being blown out the drain. If you put caps on those uprights you may hear gurgling from the air being blown down the drain line.

The trap at the sink keeps the sewer gas from coming back up the drain line into the air handler. You could replace that hose with something softer if you can find the right size.

 

The pan drains go directly to separate outside drains under the roof overhang eve of the house.

If I put a trap on each condensate drip line and cap the stubs, is that air pressure in the line not enough to push the water through the trap?

 

That's the proper way to drain the overflow pans. If you ever see water coming out of there you know there is trouble.

The air pressure will not push air thru a trap at the unit.

 

Looks like I have some work to do up there.

Thank you for all the information!

 

It's really simple - Treat the drain lines. And this is actually something you can do yourself, or pay AC guy to come out and do when he performs maintenance (it's apart of HVAC maintenance). But you really should learn to do it yourself it will save you money and it's just something everyone needs to to learn to do if they own a home.

Think of the drain's like a swimming pool, over time if left un-treated the swimming pool will grow all kinds of gunk and slime and sludge. Well the same thing happens to the HVAC drain lines, except the drain lines get clogged and overflow into your house =(

You can pick up the condensate pan tabs that HVAC technicians use at hardware stores, or order them online. They are usually listed under "condensate pan tablets". So all you have to do is pick up the tablets and follow the instructions. In the picture posted above, your first picture of your evaporator coil, you'll see the a white PVC pipe sticking straight up , it's called a 'Tee', and your's is located near the evaporator coil right after the drain line makes a sharp 90 degree turn as it exits the coil. Buy the tablets, and throw them down that hole in the pipe sticking straight up (you may have to break them in half, no big deal). They will melt over time, and dissolve as the AC system runs, and coat that whole drain line and keep the nasty stuff from growing and clogging the drain.

Your specific set-up drains into a sink, which we all hate because these clog very frequently. You'll need to cut that hose, because its crimped, and clean out everything in the trap and the hose. You'll have to disconnect the P-Trap on the sink, followed by the junction that the drain line hose is attached to, and clean all this out.. Once you pull these pieces off and look inside them, you'll see why they clog so easily and why they have to be treated so frequently. Plus people tend to stick all kinds of things down the bathroom sink, hair, shaving cream, ect, this all eventually helps clog the area where your AC drain line connects to your sink.

Pick up the tabs, follow the instructions on the tabs, use how many they tell you to use, and use them as often as they tell you to use them. Some tabs last longer than others, some are cheap, some are really expensive.

Now, if your drain is completely clogged, these tablets are not going to unclog it, and never pour drain cleaner down the drain line.. If it's clogged you have to manually unclog the drain line with a wet vac or by blowing compressed air of some sort through the drain line to dislodge the clog. But be careful when blowing compressed air through a drain line, try to stick with a wet vac.

You have to keep the drains treated, because once the slime and sludge and gunk builds up you're going to start creating permanent problems as cooling seasons and heating seasons cycle year by year.. So once heating season rolls around and you stop running the AC system, the AC system will stop draining.. And all that slime and sludge and gunk solidifies into like a calcium-like substance that's almost impossible to clean out without replacing the whole damn drain line. So layer by layer, season by season, you slowly turn your entire drain line into a permanently clogged solid calcium stick of uselessness. So don't let this happen, save yourself the trouble treat the drain lines, fix/cut your hose to proper size so it isn't kinked and bent under the sink (it's going to clog there if you don't), and install a float switch on the drain pan. Here's some ac drain line maintenance tips and instructions that explain things a little better:

 

Gas furnaces like yours can have drain lines that connect to each other.
Electric air handlers cannot.
This is because inside a gas furnace, the blower motor is before the evaporator coil, and the blower motor blows air accross the coil, in essence creating a positive pressure infront of the fan and inside the evaporator coil where the drains are located.

In an air handler, the blower motor is AFTER the evaporator coil, and it pulls air accross the coil where the drains are located, in essence creating a negative pressure inside the evaporator coil.. This is why traps have to be installed on air handlers, because the negative pressure created by the fan inside the air handlers cabinet will literally suck the water backwards and into the air handler and it will never drain.

What you have is a gas furnace, with a slab evaporator coil, and a P-Trap isn't necessary, and drains can also be tied into each other as long as the 'Tee' is present in both drain lines to allow air to pass over the water in the drain without forcing the water backwards into the other system.

 

Sorry I'm just now seeing this reply. Thank you for the detail.

You're saying my setup doesn't need a trap installed...would it be beneficial to have one even if it isn't necessary? If so, I'm guessing before the T? If I should just leave the system as is (minus fixing the black kinked hose), should I put a cap on the top of the T? There is definitely cold air blowing out of the T when the system is on. I've already bought a trap kit with overflow sensor, but they aren't yet installed.

Seems like the two replies here are conflicting. Any additional clarification is greatly appreciated.

 

I always opt for a trap. In your case that upright pipe would be past the trap and there would be no cold air coming out.