Did a house yesterday the primary condensate drain line was angled in such a way that it was higher than the secondary. The secondary drain had a constant stream to a consistent drip going from the soffit. So when I get to the master bath and hear a (best description to mind but not a good one) bubbling kind of sound. Sort of like if you were drinking from a straw and were at that last small amount of drink at the bottom and slowing causing it to make the sound.
I look under the sink and see that this appears to be where the primary drain is tapped in.
Is this something you veterans run across from time to time?
The primary condensate drain in the attic needs a trap or the trap is not working adequately and air is blowing past the trap weir. A proper functioning trap in the attic will typically stop the noise at the plumbing fixture. Correcting the primary vs secondary elevation may also help correct this.
There are a number of piping mistakes made when installing a condensate trap. In my opinion, an open clean-out between the trap and coil is the number one mistake. I believe it’s made because installers think leaving the pipe open will help the system drain, working much as a vent does on the house plumbing. When in fact, an open clean-out at this location allows air to bypass the trap altogether. This mistake is easily corrected by placing a cap over the clean-out pipe and only removing it for cleaning purposes. It should be easy to remove, so gluing is unnecessary (see photo above).
Here in N.Texas we call out the primary condensate p-trap if it is not insulated. The reason is and I can show you pictures to back it up. The cold primary condensate line (ironically) condensates due to the high heat and humidity in the attic and drips.