95% furnace condensation question

[Marc M]

This unit was installed only a day before i arrived. I noticed that there was condensation immediately draining from the condensate I labeled as "B" in the image, and filling the pan. This condensate drained directly into the pan.
The pan has a shutoff switch so there was no secondary to the exterior. I noticed that the vent condensate was tied into the "A" condensate I labeled. There was no trap on the vent condensate because it was tied into the "primary" after its trap.
My question is, any idea how come the "B" condensate would start to drain so quickly? Perhaps the primary and secondary are switched/blocked?

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[Lon Henderson]

I have never seen a pan with a shutoff switch. I don't understand how that works. Maybe this a regional lingo difference?

[Scott Patterson]

Most likely the unit is not level and it is angled so the condensate is flowing back toward the secondary drain. So, as the pan fills it flows out the secondary drain.

In the photo it looks like the unit is angled toward the secondary drain. They must be level! How many times have you ever seen an HVAC contractor with a bubble level? I can't recall ever seeing one with it in hand or even near a job the were installing.

[Marc M]

Most likely the unit is not level and it is angled so the condensate is flowing back toward the secondary drain. So, as the pan fills it flows out the secondary drain.

In the photo it looks like the unit is angled toward the secondary drain. They must be level! How many times have you ever seen an HVAC contractor with a bubble level? I can't recall ever seeing one with it in hand or even near a job the were installing.

Yes, excellent point, thanks Scott.

[Dom D'Agostino]

I have never seen a pan with a shutoff switch. I don't understand how that works. Maybe this a regional lingo difference?

Unit leaks, pan fills up, unit shuts off, owner calls HVAC tech,

Bring your shop-Vac up there to drain the water....

[Lon Henderson]

Unit leaks, pan fills up, unit shuts off, owner calls HVAC tech,

Bring your shop-Vac up there to drain the water....

Yup, never have seen one of those type switches used on a drain pan. But I like it.

[Paul Balutis]

See them all the time in new attic installations here in Mass. Sometimes the switch and the pigtails are there, but not connected, so check carefully . Stops the unit and prevents expensive ceiling damage below, etc.

[David Bertrams]

In my AHJ, the safety switch is not allowed if the secondary can drain by gravity.

[Scott Patterson]

In my AHJ, the safety switch is not allowed if the secondary can drain by gravity.

Not allowed?

I see them all the time simply as a backup to the secondary drain, even if it is draining to the exterior. You can never be too safe...

I'm also seeing more secondary drains that terminate after a few inches and have a float/sensor switch in the pipe, if it detects water it shuts the system off.

[Jerry Peck]

In my AHJ, the safety switch is not allowed if the secondary can drain by gravity.

"can"?

Anything "can" be done, not all things can be done easily, but you did not say "can be done easily".

[Lon Henderson]

Not allowed?

I see them all the time simply as a backup to the secondary drain, even if it is draining to the exterior. You can never be too safe...

I'm also seeing more secondary drains that terminate after a few inches and have a float/sensor switch in the pipe, if it detects water it shuts the system off.

Amazing how different things can be in different regions. You see them all the time, and I have never seen anything like that. But Murphy's Law now says that I will see one on my next inspection.

[William McElheny]

Marc,

What was running? Furnace or A/C.
If furnace was running then the main drain may be clogged and condesate is backing up in "A" and draining out "B".
If A/C was running it could be because unit is not level or main drain is clogged.

I have over 40 years of HVAC work under my belt and have many bubble levels and use them on every job. But then again I am old school and take pride in my work.

[Marc M]

Marc,

What was running? Furnace or A/C.

Furnace.

[William McElheny]

Marc,

If furnace was running you should not be getting anything out of "B" this is a back-up for "A" drain if it is clogged.

This makes me think main drain is clogged and condensate from the furnace is backing up through "A" and spilling out "B".

[William McElheny]

Marc,

A/B drains are for the condensate from the evaporater coil when in the A/C mode.

[Marc M]

Marc,

A/B drains are for the condensate from the evaporater coil when in the A/C mode.

Thats what i said, but the HVAC guy said i didnt know what I was talking about. Probably for fear of looking like a dumb A.

[Rich Goeken]

In my AHJ, the safety switch is not allowed if the secondary can drain by gravity.

How can the AHJ tell you not to have a device such as a safety (water damage) switch?
If that was said to me, and the pan filled and overflowed causing damage, that person would be responsible (as far as I am concerned) for the bill.
That person maybe said that it is not required in your area, but you can install it if you want.
Notice that many condensate pump manufacturers are installing overflow alarm switches as standard on their models.

[Rich Goeken]

This unit was installed only a day before i arrived. I noticed that there was condensation immediately draining from the condensate I labeled as "B" in the image, and filling the pan. This condensate drained directly into the pan.
The pan has a shutoff switch so there was no secondary to the exterior. I noticed that the vent condensate was tied into the "A" condensate I labeled. There was no trap on the vent condensate because it was tied into the "primary" after its trap.
My question is, any idea how come the "B" condensate would start to drain so quickly? Perhaps the primary and secondary are switched/blocked?

What everyone has said about the B drain is correct. If you notice, it is a little higher than the A
drain. It is really a backup drain that would function when the main drain is blocked with "stuff"
and functions to prevent overflow within the furnace.
The B drain, when connected, should go to a visible area where it will be noticed if it discharges
water. It is an indicator that the main drain is clogged. It should never be installed such as you
see it in your photo. You didn't mention the drip pan. How is that drained? Drip pans would be treated
the same way a B drain is treated and go to a visible area with some installations having a float alarm
for the pan.
The drip pan drain should not be combined with the condensate drain and should be piped separately.

[David Bell]

If it was leaking in heating mode then the drain is clogged after the furnace drain is tied in backing up to the A/C coil.