Got a question for any HVAC guys....., is the large pan under the HVAC units in the attic only for emergency overflow if the main drain is plugged? My a/c units have 2 drain lines coming out of the condenser area, 1 has a curved trap with an open "stack" and empties into a bathroom sink drain, the other just dumps into the large pan and empties under the eaves outside. My main line isn't plugged....., I cleaned the trap under the sink and water was trickling through that condenser drain line. I'm also getting a steady drip into the large catch pan under the unit in the attic......., is it normal to be draining from bogh lines?

Not an expert but have had this problem before, we had a floating plug of gunk inside of the air handler that would partially plug of the main drain. We blew through the main drain and it was not plugged off until the floating plug moved back over to it. We had to open up the air handler and clean out the inside. Good luck.

A little more checking and I'm pretty sure I have a block in the line. I tried the shop vac trick where it dumps into the sink drain but no go. I reckon I'll see if Home Depot has a small snake and maybe give that a try. Anybody have any other good tricks?

Sounds like you need to clean the pan and flush the drain. The primary drain that drains into your bathroom sink is the only one that should normally be producing water. The overflow or seconday drain is routed to an area where you will notice it leaking. This lets you know you have a problem with your unit. Make sure you kill the power to the indoor and outdoor unit to be safe. Clean the pan and flush the primary drain line. Good luck.

That's my problem....., haven't been able to get the primary line flushed out. Tried pulling it out with the shop vac, tried blowing air into it, treated with a little bleach - but still clogged. Might try a small flexible snake tomorrow.

The pipes that drain your unit (to the bathroom drain pipe) might have a U-shaped trap in them as mine do. As with a kitchen sink, these can be the first place to check for a clog.

But a cap of bleach or vinegar in the primary and secondary drain lines each time you change your filters. It will help prevent the clogging, which is usually algae of some kind.

Boiling (or very, very hot) water works well to break down the "jelly" that blocks the lines. The best way is to get it directly in the piping so that it doesn't cool off by sitting in the pan.

Ended up clearing the line by blowing compressed air through it. Will get in the habit of pouring a little bleach through 'em every so often. Thanks for the tips!

My AC guy said to pour a bleach/water solution down the condensate line about once or twice year. Just be careful to not get carried away with the bleach if you are in the country on a septic system. It can kill the bacterial in your septic system.

On second thought, since you had a blockage you might just go ahead and run some liquid drain cleaner through it. Your compressed air may have just cleared a small passage. Just be sure to flush it with water. I don't know if just the slow drip of the AC would rinse the drain cleaner out in a timely manner.

Why would somebody put a trap on A/C Condensation line if the line goes into the drain of the bathroom sink?

Besides the trap there is a float switch on there. If the drain line stops up then the water will rise in the trap and float the switch and shut down the unit. If that fails, which they do, then that is what the big galvanized pan is for. The line from the pan is supposed to go to a "conspicuous" location, such as a garage ceiling, the soffit near a door, etc. so that you will see that you have a problem.

Those float switches aren't all that reliable. They get gunked up and stick to the walls of the pipe, just like a seized piston in a sleeve. In fact the newer ones come with a little brush on a flexible line for you to clean it out periodically, which I am about to go do now.

This thread was a reminder for me--brush out the trap and pour in some bleach solution. This is what mine looks like.

https://www.acwholesalers.com/Airtec-Gri...CFZCEaQodPIgARA

As I mentioned in another thread, I added a T- section of PVC pipe, with a short, vertical riser near each air unit, as well as the exit point from the attic space, for the sole purpose of being able to pour a little bleach into lines once a year. A short, vertical extension was added to each T section to make it easier to pour the bleach, along with a good amount of water, into the line using a funnel. An unglued end cap was added to each to keep other dust and trash from entering the lines. In essence, they serve the same purpose as a clean out in other drain pipe applications.

Heavy-duty trimmer string (.095 or .105 ) makes a great/safe/cheap 'snake' for loosening the goop in the line, fyi . . . .

A properly vented trap insures the condensate line will drain. The vented trap isolates the drain line from the air pressure difference in duct system.