Author Topic: HVAC condensate drain air flow and cleaning  (Read 4806 times)

forummm

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HVAC condensate drain air flow and cleaning
« on: July 08, 2015, 08:57:16 AM »
I had my compressor and coil replaced. And now I notice that some cold air is blowing out the condensate drain pipe attached to the blower. It's not a ton of air, but enough that it blows the loose-fitting cap off of it (the cap I take off to pour bleach water down to clean it out). Obviously this is wasting some of the cold air (the blower is in the attic). Should I be worried or have them fix anything?

Also, I see a bunch of youtube videos saying that you should occasionally use a wet/dry vac to clean out your condensate line in humid climates because of the algae and mold that can grow. When I do that do I leave the condensate line cap on (so that it will suck from inside the blower) or take it off (so that it will just clean the portion of the line outside the blower)?

Rollin

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Re: HVAC condensate drain air flow and cleaning
« Reply #1 on: July 08, 2015, 09:19:13 AM »
I thought there was supposed to be a water trap on those that would not allow air to flow out...  Might be a bad memory though :(  Maybe a silly question, but is the new blower blowing in the correct direction, and not reversed?

Just guessing, but I'd be interested in what you discover.

forummm

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Re: HVAC condensate drain air flow and cleaning
« Reply #2 on: July 08, 2015, 09:28:05 AM »
It's the old blower. Just the coil and compressor were replaced. I don't know what it looks like inside.

And the blower is blowing the correct direction (air exiting vents, going into intakes).

guitar_stitch

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Re: HVAC condensate drain air flow and cleaning
« Reply #3 on: July 09, 2015, 10:11:14 AM »
That's not right at all.  The line, if anything, should have negative pressure on it, sucking air through it.

Rollin

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Re: HVAC condensate drain air flow and cleaning
« Reply #4 on: July 09, 2015, 11:10:05 AM »
That's not right at all.  The line, if anything, should have negative pressure on it, sucking air through it.

...if the water trap is dry (assuming there is one).

Is the drain line completely free of debris (mold and gunk)?  Sometimes this will cause weird pressure differences. 
anyway, it should be cleaned regularly regardless, as an overflow can cave in your ceiling (twice, DAMHIK).

forummm

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Re: HVAC condensate drain air flow and cleaning
« Reply #5 on: July 09, 2015, 11:29:01 AM »
That's not right at all.  The line, if anything, should have negative pressure on it, sucking air through it.

...if the water trap is dry (assuming there is one).

Is the drain line completely free of debris (mold and gunk)?  Sometimes this will cause weird pressure differences. 
anyway, it should be cleaned regularly regardless, as an overflow can cave in your ceiling (twice, DAMHIK).

Cap on or off? See:

Also, I see a bunch of youtube videos saying that you should occasionally use a wet/dry vac to clean out your condensate line in humid climates because of the algae and mold that can grow. When I do that do I leave the condensate line cap on (so that it will suck from inside the blower) or take it off (so that it will just clean the portion of the line outside the blower)?

guitar_stitch

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Re: HVAC condensate drain air flow and cleaning
« Reply #6 on: July 10, 2015, 01:31:08 PM »
All I have ever done with AC drains is bleach once a year.  Obviously, this requires cap-off.  To get a decent cleaning with the wet/dry vac, I would leave the cap on.  More likely, you'd need a flexible line brush to clear the drain if it's plugged.

The positive air pressure concerns me a bit.  Even if the water trap were dry, it should not be pushing air out.  The design is such that with the water trap full, the system is able to drain properly, letting gravity overcome the force of airflow in the evaporator drain pan.  The only way I could see positive pressure in the line is if the drain pan/condensate outlet was after the blower (pushing air through the evaporator instead of drawing air through it.)  I'm not an AC expert, so I won't say that's impossible, but it would be strange.

Can you see where the line exits the house?  If so, verify that there is an upward bend, turn up, or at least a 90 degree elbow that causes the line to have some water in it at all times.
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CowboyAndIndian

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Re: HVAC condensate drain air flow and cleaning
« Reply #7 on: July 10, 2015, 01:55:59 PM »
This is what I did.

Had a vertical condensate discharge, which dumps the water to a tiny pump.
Added a P-trap to the vertical line as shown in the picture.


a1smith

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Re: HVAC condensate drain air flow and cleaning
« Reply #8 on: July 25, 2015, 11:10:07 PM »
This is what I did.

Had a vertical condensate discharge, which dumps the water to a tiny pump.
Added a P-trap to the vertical line as shown in the picture.

The way you installed the P-trap will work but it really should have gone in the other way around.  Then, you would only need one elbow and a coupler instead of three elbows.

The way you have it the water backs up all the way to the height of the line on the discharge side of the P-trap.  If you install it the other way around then you only have water in the P.

Look at the P-trap under one of your sinks to see what I mean.

EDIT: However, since this a forced air system you need to check how many inches of water differential pressure you have.  Once you know that, you will know how big your loop seal needs to be.  It could be that the P-trap might not have a big enough seal on its own.
« Last Edit: July 26, 2015, 04:30:19 PM by a1smith »