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Old 06-25-2010, 09:21 PM   #1
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Condensate only drains when blower stops


After turning on our A/C for the first time this year, I noticed that no water was exiting the primary condensate drain line outside the house. Thinking it was clogged, I shop-vacíed it from the outside but it still didnít drain like I thought it should. I checked the attic unit and the large secondary overflow drain pan had about an inch of water in it. I drained it all out and then installed a valve downstream of the P-trap on the primary condensate drain line, and a hose fitting connected to a tee downstream of the valve. I then flushed out the line with a garden hose with the valve closed to block the water from flowing back into the evap coil primary pan. After running the system for a while, the secondary pan kept filling up. So after watching the unit in operation for a few minutes, I noticed water draining from the secondary drain and dumping into the secondary (external) pan. The primary drain has a P-trap, with a tee and cleanout on the upstream leg of the P. I pulled the cleanout off and immediately the water stopped draining from the secondary and I could see a lot flowing through the primary. Also, a lot of air was flowing out of the cleanout since the evap coil is on the positive side of the blower.

I took the access panel off and verified that the primary drain is installed on the deeper side of the pan and the secondary drain is positioned higher (also has a pinhole restriction bringing it even higher relative to the water level). I recently started running the blower 24/7 to keep air circulating in the house to keep the temps even, and I think the way the air blows around in the evap coil compartment is keeping water from flowing out through the primary drain. I had also reinstalled the cleanout pipe last year that had been removed and left lying on the floor of the attic by someone past. Running the blower only when the compressor is on, the secondary pan doesnít fill up, but a small amount of water is seen coming from the secondary drain and evident in the pan, which evaporates quickly in the attic heat.

I cleaned the coil with foam and rinsed it, so I donít think itís a flow issue through the coils themselves. I use the highest rated air filters and change them every three months (I have 3 total, different sizes), so I donít think air flow restriction through the coils caused by dirt is an issue. The coil is installed with the A turned 90 degrees (horizontal system) with the tip of the A pointing in the direction of air flow. The drain lines are installed at the base of the A, nearest the blower.

To me it sounds like poor design. I guess itís possible the primary pan could be installed 180 degrees opposite its current position, with the deep end away from the blower but I have no idea if this is permitted or normal. I was also thinking I could remove the cleanout from the tee and connect it to a pipe run over to the negative side of the blower, decreasing the pressure at the primary drain.

Any thoughts? I hope that all made sense.

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Old 06-25-2010, 09:46 PM   #2
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Condensate only drains when blower stops


Thats a LOT of words. Take some pics of it and post them here (manage attachments) or the links to photobucket here. We really need to see what you have. I have had to put open tees on the drain where it leaves the coil and sometimes add a vertical extension piece or pipe or clear tubing on the tee to break the vacuum or alter the pressure on the drain so it will flow properly. Takes some trial and error to get it right. Did someone change the fan speed recently?

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Last edited by yuri; 06-25-2010 at 09:49 PM.
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Old 06-25-2010, 09:57 PM   #3
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Condensate only drains when blower stops


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Originally Posted by yuri View Post
Thats a LOT of words. Take some pics of it and post them here or the links to photobucket here. We really need to see what you have.
Yeah sorry for the thousand words; a picture is much better. Attached is the best pic I have for now.

Quote:
Originally Posted by yuri View Post
I have had to put open tees on the drain where it leaves the coil
If the tee is open, cold air blows into the attic. I can't imagine that would be good for efficiency.

Quote:
Originally Posted by yuri View Post
and sometimes add a vertical extension piece or pipe or clear tubing on the tee to break the vacuum or alter the pressure on the drain so it will flow properly. Takes some trial and error to get it right. Did someone change the fan speed recently?
You mean if the vertical portion of the tee is longer, it modifies the pressure in the drain? That's interesting. Didn't know changing the fan speed was possible, but I had begun running it constantly, which is what caused the overflow pan to fill up. But no, the speed hasn't been changed.

Thanks for the response!
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Condensate only drains when blower stops-img00096-20100603-1737-3-.jpg  
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Old 06-25-2010, 10:07 PM   #4
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Condensate only drains when blower stops


Elaborate a bit about those three highest rated filters. Hopefully you don't have three of the 3m filters in one system.
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Old 06-25-2010, 11:14 PM   #5
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Condensate only drains when blower stops


Yeah, is that not good? The whole family has allergies and they seem to help.

3M Filtrete Ultimate and Elite Allergen filters:

20x25 - 2200 MPR
14x20 - 1900 MPR
12x12 - 1900 MPR
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Old 06-26-2010, 06:41 AM   #6
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Condensate only drains when blower stops


What size is the A/C?

Take another pic or 2 of the case coil set up. So we can see how the plenum is attached to it, and how the duct work is attached to the plenum.
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Old 06-26-2010, 07:15 AM   #7
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Condensate only drains when blower stops


why are there 2 PVC lines off that air handler...do they both connect inside to the pan?the emergency pan shouldn't have a white drain pipe run to it it is only installed when the pan overflows and hits the insulation and drips out the panels...and the one shown that looks like the main condensate drain doesn't have a trap on it.there aren't options to install on the neg/pos sides it is the design where the coil and fan are that gives it that result....either or they have to be trapped
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Old 06-26-2010, 08:44 AM   #8
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Condensate only drains when blower stops


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why are there 2 PVC lines off that air handler...do they both connect inside to the pan?the emergency pan shouldn't have a white drain pipe run to it it is only installed when the pan overflows and hits the insulation and drips out the panels...and the one shown that looks like the main condensate drain doesn't have a trap on it.there aren't options to install on the neg/pos sides it is the design where the coil and fan are that gives it that result....either or they have to be trapped
Looks to me like there's a trap in the primary side but it's in backwards. Around here there's a good chance that trap would freeze and break before drying out. Secondary goes into the emergancy overflow pan which is the piped seperate. Perfectly acceptable to do that but I prefer a float switch. Secondary has to be used here if the unit is in a hidden place, can't leave the plug in and jut let it overflow the coil into an emergancy pan.
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Old 06-26-2010, 09:01 AM   #9
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Condensate only drains when blower stops


Here are some better pictures.

Secondary pan has a float switch and also a drain that runs outside next to the primary drain line.
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Condensate only drains when blower stops-dscn4801.jpg   Condensate only drains when blower stops-dscn4802.jpg   Condensate only drains when blower stops-dscn4803.jpg  
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Old 06-26-2010, 09:12 AM   #10
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Condensate only drains when blower stops


Take a piece of duct tape(or whatever). Put it over the secondary drain line, so it traps the water it there. Then see if the primary drains better.

Looks like you may have a velocity problem through the coil. The air may be carrying the condensate past the primary drain and pushing it out the secondary.

If so. Just install a small trap on the secondary(running trap, so it evaporates the water come heating season).
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Old 06-26-2010, 09:51 AM   #11
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Condensate only drains when blower stops


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Take a piece of duct tape(or whatever). Put it over the secondary drain line, so it traps the water it there. Then see if the primary drains better.
I tried capping it before. The internal pan just fills up until the blower shuts off. Then all the built-up water in the pan rushes out the primary.

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Looks like you may have a velocity problem through the coil. The air may be carrying the condensate past the primary drain and pushing it out the secondary.

If so. Just install a small trap on the secondary(running trap, so it evaporates the water come heating season).
This is sort of what I was thinking. Bad design?
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Old 06-26-2010, 09:57 AM   #12
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Condensate only drains when blower stops


Not a bad design. As much as probably not set up right.

Can you measure the air temp at the return of the furnace. And in the plenum right after the coil.
If not. then the temps at the nearest return grille and nearest supply register. Thats not as good as knowing what the temps are at the unit though.

Along with model number of the outdoor unit, the indoor coil, and the furnace model number. Furnace model number is inside the burner compartment.

With that info. We know what size your equipment is, and what size blower your furnace has. Along with temp rise across the coil. We may be able to determine if the air flow is set too high.
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Old 06-26-2010, 10:25 AM   #13
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Condensate only drains when blower stops


You need an airgap...put the trap first and the airgap second.
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Old 06-26-2010, 10:47 AM   #14
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Condensate only drains when blower stops


Quote:
Originally Posted by beenthere View Post
Not a bad design. As much as probably not set up right.

Can you measure the air temp at the return of the furnace. And in the plenum right after the coil.
If not. then the temps at the nearest return grille and nearest supply register. Thats not as good as knowing what the temps are at the unit though.

Along with model number of the outdoor unit, the indoor coil, and the furnace model number. Furnace model number is inside the burner compartment.

With that info. We know what size your equipment is, and what size blower your furnace has. Along with temp rise across the coil. We may be able to determine if the air flow is set too high.
I'll get that info ASAP
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Old 06-26-2010, 10:48 AM   #15
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Condensate only drains when blower stops


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Originally Posted by Marbledust View Post
You need an airgap...put the trap first and the airgap second.
An airgap?

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