Does this sound right..... Again, I have to say I'm refrigeration not HVAC.
That being said I visit my aging parents several time a year in Florida. As I passed the gigantic Plenum in the hallway I heard dripping sounds. Turned out the condensation drain at the air handler backed up because of some jack asses who didn't glue them properly during construction. The plenum flooded and I got left with a huge job and a insurance claim because of the mold. I digress.... upon further inspection I noticed no other return heading into this plenum that sits directly under the air handler. I went into the attic and noticed 3 returns in the front of the house and 2 returns in the back of the house were "closed loop". I'm not proficient in HVAC but I was under the impression all the returns go to the Plenum to blend and distribute the air back into the air handler.
So my question........ is closed loop returns a practice that i'm unaware of or just lazy installers?
thanks for any input.