What's this device (circled in blue) that's attached to my furnace? It recently got replaced and I forgot what the HVAC technician called it, or what its function is.
I do rember that they said to put some vinegar in the U-bend (circled in red) once or twice a year. I forgot to ask why this is necessary, but I'd guess that it tends to collect moisture, and the vinegar will prevent mold?
That's the condensation pump. Without it, your furnace would build up condensation.
It wouldn't build up, it would just spill onto the floor. Houses with drains near the furnace don't need these pumps.
It builds up condensation anyway; this just removes it