Central A/C Mainline Drain Clean Questions

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Old 07-01-15, 09:41 AM
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Central A/C Mainline Drain Clean Questions

Hi All,

First time post thanks in advance everyone for your feedback. I have a new house (built 2014) with Central A/C (Carrier Unit) and the FAU is upstairs in the attic above the 2nd floor. Last night I noticed condensation drip from the pipe coming from the top of the 2nd story and got worried.

Went into the attic to check the AC unit and the secondary drain (drip pan) was about 1/8" of water build up (pain is about 1" deep). I'm in Southern CA and it's been a bit hot and humid lately so thought it may just be moisture buildup on the condensers draining into the overflow but not sure if this is normal without the main drain being backed up.

After doing some online research, I found many sites/users saying that any water in the drip pan usually means that the main line is blocked/clogged and needs to be unblocked via 2 methods. First finding the location of where the main line drains (found mine in a 2nd story bathroom) and 2nd pouring bleach into the line near the unit to clean the dirt/gunk that may be stuck there.

My problem (or so I think) is that most online images I could find have an open pipe on the mainline drain that is upline from the P-Trap so that whatever you pour into it will clean the clogs in the P-Trap, but this one looks like whatever I pour into it will bypass the P-Trap. All the other joints were sealed upon installation and I'm probably not handy enough to remove the seal to clear any clog annually then reseal.

My questions:

1) If it's humid out, is it normal (possible) for there to be water in the drain pan (secondary drain) while running the central AC?
2) Does any water in the drain pan always mean that the main line is clogged?
3) Looking at the image (below) should I pour bleach into the open pipe or will this not do any good since it seems downstream from the P-Trap?
4) The mainline drains to the 2nd story guest bathroom. Should I unhook this drain and use a shopvac to try and suck out any obstructions?
5) Any other tips based on the image shown?

Thanks!

 
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Old 07-01-15, 10:24 AM
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Yes if you have water in the pan the main drain is blocked.
 
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Old 07-01-15, 10:52 AM
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Thanks skaggsje. Based on the image I provided what do you think is the best way to clean the blockage?
 
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Old 07-01-15, 04:15 PM
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I'm not an expert on this subject by any means, however I would suggest pouring bleach into the open pipe. It looks like some of it will may flow "backwards" towards the trap, which is likely where the clog is. If that doesn't clear the blockage, try hooking your shop vac to the open pipe and try to suck out the clog. If that doesn't clear it, you could try closing off the main drain where it connects to the bathroom drain (if easily done).

Good luck!!
 
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Old 07-01-15, 07:08 PM
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You need to find out where the clog is first, is it in the p-trap or down the line ? May be too late to use bleach, you may have to either suck/blow it out or use sneak to clean it.
 
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Old 07-02-15, 09:00 AM
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thanks bob and clocert. This weekend I'm going to try both the bleach and the suction (from the bathroom sink upstairs and the main in attic as well). Hopefully one of those will clear the clog.

The house is only about 15 months old and we don't use the A/C too much (IMO) so the clog should be pretty minor I hope.
 
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Old 07-02-15, 10:08 AM
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Just curious, the house is a year old, why would they run the drain line to the bathroom sink? Sounds crazy to me.
 
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Old 07-06-15, 08:08 AM
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Much to my surprise, I fixed it. Did the following:

1) Unhooked the pipe from the drainage point (2nd floor bathroom) and shop vac'd for 3 min. Got about 1/4" of water in the shop vac but didn't notice anything really gunky.
2) Went up in the attic and shop vac'd through the open PVC for about 1 minute. Got much less water but still some.
3) Poured 1 cup bleach into the open PVC (waited 30 min to turn on the A/C so it could do it's thing)
4) Blotted up all the standing water in the drain pan to ensure if I found drips that it wasn't due to the existing built up water.
5) Put a bucket outside to catch any drips from the 2nd story secondary drain pipe
6) Turned A/C on overnight, waited.

This morning I went out and not a single drip in the bucket. I was like 90% sure it would still be dripping but for once I'm glad to be wrong. I'll keep an eye on it but probably saved myself some $ this time.
 
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Old 07-06-15, 11:31 AM
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My experience ,if you tape over the open pipe then use shop vac at outlet end you will not only clean trap but opening in unit where condensate enters the pipe.
 
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