The coil on my furnace sits in a drain pan that has two drain ports side by side except one of them has a smaller hole and is slightly higher than the other. Is there some reason why the installer would have tapped into the smaller high port rather than the larger (lower) port? Why are there two ports anyway? Is the high port a backup in case the low port plugs up? Seems to me the small hole in the high port would more easily clog from dust/lint.
The A/C was installed new last year and hardly got any use but I had observed condensate in the clear tubing the installer ran over to the sump pit. I just started up the A/C yesterday for the first time this year and noticed there was no condensate in the drain line so I figured maybe it clogged up with dust/lint that collected over the heating season. I popped off the side panel and the drain pan had standing water and the base of the coil all rusted from sitting in the water. It just doesn't seem right to me that metal would be sitting in water like that. Even the lower of the two ports would leave a little bit of standing water in the pan, not as bad as the high port but none the less enough for the metal to rust.
The installer screwed a 1/2" reducer into the 3/4" port, so that naturally raises the water level in the pan. Since the threads on the port are even with the bottom of the pan, the height to the inside of the 1/2" reducer means that 1/2" of water will sit in the pan. It sure looks like a piss poor design and an even worse install job.
I'm thinking I should look for a thinner walled brass 3/4" nipple and a Tee to drop down before reducing to 1/2". That would lower the water level in the pan. Since the drain doesn't connect to the sewer, I don't need a trap so I could also put a riser on the top of the Tee as a vent so that air blows out the port and helps move the water along.
Keep it 3/4"! IT should be plumbed to the lower port. It's not a bad idea to plumb a second one to the upper port. It IS there as an emergency backup - not the primary. This should all be described in the installation manual which the installer SHOULD have left with you.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013