P-trap on a positive pressure coil

bauer

I am investigating an issue with an EZ-trap on a positive pressure evap coil ---

The condensate line has an EZ-Trap 200 -- when the float switch & red cleaning cap are installed, it seems the positive pressure from the blower fan is preventing water from draining, thus eventually draining out of the secondary drain line. If you remove either the float switch cap, or red cleaning cap, water flows freely and exits outside (no clogs along the main line). The vent on the downstream side of the trap is clear.

I can post a picture if necessary, but it is a typical set-up of the EZ-Trap 200

EdTheHeaterMan

The reason for the Trap is to overcome the negative pressure of the blower inside the cabinet of the standard air handler, so there is no air getting sucked into the coil box when the fan is operating. Air being sucked into the drain opening will prevent water from leaving the drain pan. If you have a positive pressure on your drain, because the coil is on the discharge side of the fan (as you would have on a furnace) the trap has a different function. I would like to see the set up.

Signed
Waiting for pictures.

SuperTech

I would think that the trap isn't necessary on a positive pressure coil, like a furnace with a coil above it. Why is there a trap? What does the manufacturers installation manual recommend?

bauer

Per manufacture instructions, a trap in a blow-through application prevents conditioned air from escaping. They do show a shallow trap design in this instance however, could that be the issue? (Secondary drain line removed for troubleshooting in picture) 

EdTheHeaterMan

Picture does not tell the full story. Where is the coil in relationship to the blower?

And why do you not have a secondary drain pan under the coil? Just so you know, This is my bathroom ceiling in the home I purchased in 2021. The air handler is only 4 years old, and the original installer installed a float switch that has not shut off my compressor. Now I need to wait for a service tech, since Im stuck in this damn wheelchair.

bauer

Coil is after the blower. Positive pressure. Air is blowing out of the coil side of trap when opened 

bauer

I agree, there should be a drain pan...

Here is the manufacturer reference to a trap on the blow-through coil

I am sorry to hear about your situation... I wish more techs would take condensation lines more seriously as they are a major liability...

ratio

Is that a 4-way fitting where the float switch goes in? Plug the open end. IIRC that's where the red cap is supposed to go, the far end of the trap needs to be open to vent.

ratio

I was close...

bauer

That is the problem....

When the open end is plugged with the red cap, and the float switch is installed.... the positive pressure is preventing the condensate from draining through the trap.

bauer

ratio said:

I was close...

this is the configuration it was in, and it was creating the blockage that backed up into the secondary drain

ratio

No, it's not. Put the trap back together & cut the PVC downstream a little ways & see if it'll drain into a bucket. I think you've got a sag or something like that in the line somewhere that's causing a double trap.

EdTheHeaterMan

What is the configuration of the drain pipe on the discharge side of the trap? Are there any turns or unusual fittings at the end of the line? What you are describing does not make sense. (That's why you are here. Dah!). at some point there is a blockage of something (like water trapped) down stream of the EZtrap. When you open one of the red caps, you create a "vacuum break" that allows the weight of the water to overcome the blockage downstream. Is there a free opening at the end of the drain, is it under a rock or in the grass or below a puddle of water?

I believe the exit end must be at least 6" above the ground so you can see the water coming out. (and you didn't just stop it right outside the attic soffit facia board and expect it to run down the rain gutter . LOL)

EDIT.. Could the positive pressure be blowing the pressure switch float down so much that it blocks off the opening to the bottom of the cross fitting.?

ratio

EdTheHeaterMan said:

EDIT.. Could the positive pressure be blowing the pressure switch float down so much that it blocks off the opening to the bottom of the cross fitting.?

I don't think so. Those are stiff plastic, it would be pretty hard for a few inches of pressure to move them.

EdTheHeaterMan

I have installed them on some systems later in my career. Not the biggest fan of the switch, but I liked the clear trap and cool brush that comes with it. Have you ever tried to use that brush on other traps and when you pull them out the brush head pulls off and gets stuck inside the condensate pipe? Ask me how I know?

neilc

the far side of the trap from the coil, needs to be vented,
what is that black riser on the far drain side ?
that should be an open vent, usually higher than the coil pan

bauer

yes, the black riser on the far drain side is a vent.

with the red cap off, the line drains outside, about 6' off the ground and I can see it running smooth

bauer

I will investigate further down the condensate drain line tomorrow and report back....thanks for the input thus far

HVACNUT

neilc said:

the far side of the trap from the coil, needs to be vented, what is that black riser on the far drain side ? that should be an open vent, usually higher than the coil pan

That is a vent.

EBEBRATT-Ed

You need a vent after the trap to prevent the trap from syphoning dry. You need a trap large enough to hold a column of water large enough to prevent the positive air pressure from breaking the water seal.

I put trap on every unit negative or positive pressure

clammy

I agree w ed on the installation of a trap whether on discharge or return side as I know it this is standard practice and I be been doing it for close to 40: years at this point I don’t argue w anybody about I just know that I never have issue unless there other issues like excessive static pressure in the supply blowing the trap dry . From the looks of it the installer must be a tool who and I mean who installs a unit in an attic w no secondary pan some one w limit experience. Your install and their company should be held responsible for the damaged ceiling and the mold . This is not rocket science it’s quite easy to follow directions and the leakage is completely uncalled for . I guess it’s not standard practice to fill a trap and ensure it drains nor put water in the pan to ensure it drains . . As for those who excessively pitch their air handler to one side towards the drainage has not read the instructions to well . Every air handler I be every installed level and have yet to have an issue w pan drainage . I like the easy trap idea but I fell the trap could be a little deeper and if the switch is opening I would look to undersized supply duct and or under sized returns depending upon where your coil is if on the positive pressure side I de be looking at high static pressure . Also ensure that the condensate line is clear and drains properly . I de ask for a more experienced tech take a look . This should not happen on a new install or on a replacement job . Peace and good luck clammy

HVACNUT

It's hard to see the application. It looks like a very shallow evaporator. 
Can you post pics of the whole setup? The air handler or furnace is below that wood planking? Is it a down flow?
It also looks like the duct on the left is sweating pretty good.

bauer

I used some clear plastic over the holes to get a visual of what was happening...

The water is flowing fine when either the float switch, or red cap is removed. As soon as you cover both of them, the water level in the trap drops, and the water flow from the coil stops completely. The positive air pressure seems to be strong enough to prevent the water from flowing through the main drain.

ratio

Did it ever drain right?

The positive air pressure isn't what's causing it to not drain, traps have worked on positive & negative pressure systems for basically ever. Did you cut the pipe to see if it'll drain then? When you say it drains with the cap off, does it drain outside properly, or does it come out the cleanout?

bauer

Yes, it drains outside properly through the trap with the cap off

bauer

Interesting note in the manual here 

EdTheHeaterMan

That note says it all. They have a known problem and they are giving you an out. Not recommending it but not prohibiting it. There are internal air flow currents near the drain openings that may cause the water to blow past the primary drain and therefor build up enough to exit the higher secondary drain. As Lt. Com. Spock of Star Fleet might say. "INTERESTING" . I might try putting a small hole in one of the red caps. Then enlarging the hole little by little in order to find the right amount of venting needed to resolve the problem. then go one size larger as a "QUALIFIED ENGINEERING ADJUSTMENT". Ask Jamie Hall what that means