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Old 09-01-2020, 12:32 PM   #1
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AC: is this exhaust supposed to be there?


I recently found several large leaks in my hvac system. One between intake duct and blower, and 2 around air handler and heater. No leaks any more, get more air, but now getting attic dust through registers. Typically at beginning for first 10-15s and then after compressor turns off. I do think itís also mixed throughout the run, but not sure. Either way, getting a lot of attic dust in the house.
I noticed a lot of air running out of the what seems like overflow exhaust (see picture, red circle). Is it supposed to?
When AC turns on, initially a lot of air gets sucked in through there, and I believe when compressor turns off as well, so it is a prime suspect. I checked all ductwork, and havenít found anything. Also, dusty air is coming through all registers, not just one place.
Is this exhaust supposed to have a valve on it?
Any other suggestions?
Thanks
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Old 09-01-2020, 12:38 PM   #2
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Re: AC: is this exhaust supposed to be there?


That’s your primary drain line. Yes it’s supposed to be there to allow condensate drainage.
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Old 09-01-2020, 12:47 PM   #3
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Re: AC: is this exhaust supposed to be there?


Are you talking about the two pipes below or specifically the open one pointing up? The two below go outside of the house and bottom one drains ok.
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Old 09-01-2020, 12:49 PM   #4
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Re: AC: is this exhaust supposed to be there?


It's supposed to be open - functions as a air vent.

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Old 09-01-2020, 12:51 PM   #5
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Re: AC: is this exhaust supposed to be there?


Ok, makes sense. Should it have a valve on it though? Seems it’s letting a lot of attic air in or something else in this setup is wrong

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Old 09-01-2020, 12:55 PM   #6
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Re: AC: is this exhaust supposed to be there?


No.

It doesn't let attic air into anything but the pipe downstream of the trap after water finishes draining.

The water in the trap prevents air from being sucked from the drain line/vent into the air handler.
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Old 09-01-2020, 02:23 PM   #7
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Re: AC: is this exhaust supposed to be there?


This is helpful, thanks.
One more question then. The pipe on the left comes straight out. There is no dip to hold the water/condensation and prevent unneeded airflow. It explains I think why there is so much air coming out from the opening, but only a little water is coming on the side of the house.
Should there be a ďdipĒ like in the picture?
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Old 09-01-2020, 02:27 PM   #8
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Re: AC: is this exhaust supposed to be there?


i didn't notice that you have a furnace, not an air handler and the drain is under positive pressure.

couldn't tell there's no trap for the angle the pic was taken from.

A trap can be added to prevent loss of supply air. It's optional in your case.
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Old 09-01-2020, 02:45 PM   #9
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Re: AC: is this exhaust supposed to be there?


I called it air handler, but I think this is heat exchanger. And you are right, the heater is on the right side of it.
If I build a trap, is it a good assumption that it wonít hurt anything?
I already know that air gets tremendously pulled in through that pipe when AC starts, until blower really pushes air through then itís coming out there like crazy
I guess thatís one question.
The other is, why is blower sucking in air from everywhere including that pipe, when I take is closer and wide open

Additionally, when compressor stops, air gets pulled in through that pipe again, even though the blower is still working for another 1-2mins
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Old 09-01-2020, 04:34 PM   #10
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Re: AC: is this exhaust supposed to be there?


The more I look at this, the more I’m certain this is messed up. There is no trap between exhaust and condensate pan. Vent is nit capped. Furthermore, the emergency drain goes to water pan and outside too, no trap. So essentially “contaminated air” is drawn in through both of these pipes. Brilliant
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Old 09-01-2020, 04:49 PM   #11
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Re: AC: is this exhaust supposed to be there?


When you have a furnace, supply air is blown out through the drain when there is no trap, it doesn't draw in air.

Adding a trap won't hurt anything if you do it properly.

However, it is an additional maintenance item, as it can get clogged and cause water to drain out the emergency connection.

You lose a little air without the trap when the unit is in the attic.
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Old 09-01-2020, 06:56 PM   #12
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Re: AC: is this exhaust supposed to be there?


Some furnaces have an internal trap. What brand and model furnace do you have?
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Old 09-01-2020, 07:01 PM   #13
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Re: AC: is this exhaust supposed to be there?


Quote:
Originally Posted by sktn77a View Post
Some furnaces have an internal trap. What brand and model furnace do you have?
We're talking about the drain on the cooling coil, not condensate for heating.

All condensing furnaces have a trap - totally different.
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Old 09-01-2020, 07:26 PM   #14
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Re: AC: is this exhaust supposed to be there?


Since there is no trap, that vent isn't serving any purpose. You can cap it or cover it with duct tape if you want to. I would recommend against making a trap if that attic gets below freezing in the winter.
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Old 09-03-2020, 03:17 PM   #15
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Re: AC: is this exhaust supposed to be there?


Thanks all. The model is GMP*-72, so Goodman.
Turns out there is a trap but made with angled pipe connectors, not standard (see left on the pic, it goes down and then up and goes out, but at a lower level than evaporator. So I guess I shouldn't cap that vent then? Air gets drawn in here for the first i'd say 5 seconds when blower turns on. After that it's blowing out.
While I was working on sealing evaporator, I vacuumed inside of plenum. What's odd to me is that plenum has that yellow fiberboard insulation, but on the inside ?!?!
Why would insulation be inside...anyways, I'm wondering if I disturbed it, and considering I plugged two rather large leaks, there is probably more air going out, so maybe that's where the dust is coming from?
I found some register filters, so I'm gonna put those in and see if they trap anything and improve air. Would be a good temp solution to this problem, especially since this weekend it's gonna be 105+.
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