P-Trap for AC Coil?

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Old 10-16-14, 12:51 PM
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P-Trap for AC Coil?

When is it necessary to have a P-Trap on an AC coil?

I believe the blower blows thru the coil... the coil is placed above a gas furnace.

I had a new AC and coil put in but the HVAC guy didn't put in a trap.

Also:
A secondary drain was not run. The secondary outlet is still plugged on the unit. Do they all have a secondary drain pan or is that an optional thing? In my particular case, there is a green plug and red plug (4 total) 2 on each side. Only one green plug was used. This installation is in a unfinished basement.
 

Last edited by ardmi; 10-16-14 at 03:31 PM.
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Old 10-16-14, 04:39 PM
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I always install a trap. I would run the sec drain to the floor. That way if you see water you'll know the primary drain is clogged.
 
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Old 10-16-14, 05:08 PM
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I almost never install a p-trap with an evaporator coil matched with a gas furnace.

I almost always install a p-trap with air handlers that use electric heat strips.

A trap is required when the evaporator coil is operating under negative pressure.

I would recommend running a secondary drain line from the evaporator coil to a pan with a float switch to prevent water from running into the furnace when the primary drain backs up.
 
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Old 10-16-14, 07:16 PM
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So to confirm, all coils have a secondary pan? And it would be nothing more than just opening that other plug next to my current drain outlet? Im not aware of how this provision works. How do I know if I have that second drain pan?

And to confirm that I am under positive pressure. I have gas furnace, the air handler is on the bottom closest to floor... that accepts the return (filter in place. The burning portion of the furnace is in the middle and the coil is on top of the furnace.
 
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Old 10-16-14, 08:36 PM
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Coils do not come with a secondary pan. They come with a secondary drain port which is higher than the primary drain port. The secondary port should be piped into a pan and a float switch should be installed on the secondary pan.

I have a furnace and coil in a closet by my living room. It did not have a secondary pan when I bought the house. I picked up a 24 by 30 inch pan and set in on the floor under the furnace ( behind the air filter). I capped the drain port on the secondary pan and installed a float switch on the secondary pan. I then piped the secondary drain port on the evaporator coil into the secondary pan. I have done this many times for customers as well.

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You could also pipe the secondary drain opening to a floor drain.
 
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Old 10-17-14, 04:54 AM
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OK, you can tell I am not very quick with this stuff.

So the pans are added in a finished space. Theres a primary "pan" inside the coil where the normal condensate collects. If that gets restricted the overflow goes to another collection point inside the coil?

So something additional or optional isn't needed to utilize that second drain port?

Can I use rubber tubing and zip tie down the side of the primary pvc drain for the secondary? And if so, what size tubing and what type of 3/4 male adapter should I use?

The coil is an Armstrong EC1P308 BG-1
 

Last edited by ardmi; 10-17-14 at 05:26 AM.
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Old 10-17-14, 06:05 AM
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If water damage is possible a pan is a great idea.
Some coils have 2 primary drain ports and 2 secondary ports that are a little higher.

A 3/4 inch brass nipple and a 3/4" female by 3/4" barbed adapter and a hose clamp can be used to run flexible tubing. Teflon tape or pipe dope should be used on the threaded males.

I have seen a small "cake" pan used as a point to run the secondary drain and float switch. Do you have a filter grill under the furnace?
 
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Old 10-17-14, 06:11 AM
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what size flex tubing do you suggest?
\
My coil has gren and red ports on left and green and red port on right. Only one green port is used. I assume the associated red port next to it is the secondanry drain.
 
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Old 10-17-14, 12:48 PM
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I would run 3/4" tubing.
Is the red port slightly higher?
 
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Old 10-17-14, 02:38 PM
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That's what confused me, the ports are sitting directly next to each other. The red port though is a bit smaller in inner diameter and I cant see anything inside of it... where the green port you can kind of see a funnel or track where water would flow.

So I was going to pipe it with tubing until I saw at the hardware store to do it in brass with poly tubing would cost over 30 bucks.... I opted for the 33 cent male adapter instead and used some scrap 3/4 sch. 40 I had in the garage. I brought it down to floor level and put a 90 there... if it overflows it will be right on the floor next to the filter compartment.
 
 

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