ONE MORE TIME...LOOK AT PHOTO. WHAT IS THIS DRAIN ?

[Gene South]

Maybe I am ignorant of just not thinking, What is this 3rd drain line on this AC. I see the main drain, the secondary and yet another one with out a PVC connection ? Look at the photo. Also, does this drain line need a PVC line that dumps into the pan ?

Thanks

Gene

[Richard Rushing]

Errr.... Gene, the secondary is draining into the pan.

The primary is on the left and past the trap, there is a vent, which is capped off.

Next one...

Richard

[Billy Stephens]

Gene,

You show a running trap in your photo ( not allowed ) needs a P Trap for that installation.

[Gene South]

Richard and Billy, I am referring to the drain opening at the far right in the photo. Is that the one you are referring to ?

[John Arnold]

This one.

[Jim Luttrall]

Looks like an unused drain on a multi position coil. Needs to be capped.
Were you getting air into or out of it with the blower on? If you had water there, something is not as it appears.

[Gene South]

Jim, it was blowing air when the unit was on and otherwise dry. No moisture.

Thanks

Gene

[Jerry Peck]

The primary condensate line needs to be trapped "properly".

The secondary condensate line needs to be "trapped" and "trapped properly".

That copper stub out looks like what Jim said, and needs to be capped.

The 'vent' (if that what it is supposed to be) going up vertically from the downstream side of the trap, looks to me like it is a 90 elbow turning back over the pan, with another 90 degree elbow turning down into the pan, and has (has had) water dripping from it. This is not going to work as a "vent", that's for sure. My guess is that the "vent" was short and it overflowed when the primary condensate line backed up, so the tech said 'I can fix that, I'll make it drain back into the pan - simple enough to do, just install 2 90 degree elbows.'

[Jim Luttrall]

What Jerry said:D

The "vent" on the primary drain line needs to be taller than the overflow of the primary pan then the secondary drain needs a trap. Oh, since the pan is now rusted out, that will need to be replaced too.

[Brent Crouse]

I'm confused. If the condensate lines run directly outside, why do they need a p-trap?

[Jerry Peck]

I'm confused. If the condensate lines run directly outside, why do they need a p-trap?

Brent,

To keep air from moving into, or out of, the AHU.

If the AHU is a blow through style, it will blow air out through those condensate lines unless there is a trap sufficiently deep enough to resist the static pressure.

Likewise for AHU which as suck through, except that they will suck air in (instead of blowing air out).

[Brent Crouse]

Makes sense to me, thanks, Jerry.

[Jake Guerrero]

Brent,

To keep air from moving into, or out of, the AHU.


What happens in the middle of January, when the trap has dried out? I think Jim L. has mentioned priming it with mineral earl (oil)..?



If the AHU is a blow through style, it will blow air out through those condensate lines unless there is a trap sufficiently deep enough to resist the static pressure.

Likewise for AHU which as suck through, except that they will suck air in (instead of blowing air out).

I think its also known as the positive and negative pressure side(s).

[Jerry Peck]

I think its also known as the positive and negative pressure side(s).

It is, but describing it as 'blow through' or 'suck through' makes a better visual understanding of what is going on.

The 'blow through' is positive pressure and the 'suck through' is negative pressure.

Plus, it not just 'positive pressure' or 'negative pressure', it's 'the static pressure' in the unit, which can be either positive or negative.

[Vern Heiler]

Worked as HVAC tech. for a couple of years 95-97. At that time we were only concerned with traps on heat-pumps with the reasoning that heat-pumps have a negative pressure or suck air at the drain opening. With air sucking into the drain line it can create an air-dam, preventing the water from draining correctly. Most of the airconditioning units have positive pressure and blow out about as hard as a nat fart after the typical 20-30' of 3/4" pipe it runs thru. Nothing wrong with trapping it but not a huge deal. (Lets em know you were looking at it when you report it.)

As far as trapping the secondary line, it may be required by mfg. but without water or some liquid in it, it is a waste of PVC. I can't convince the homie to change the filter. Do you think he is going to crawl into an attic or crawlspace with his yuppie water bottle, to prime the trap?


I still worry most about what can cost the most, condensate sweating at the trap. It'll get you called back to do some drywall repair!