Hello-

My old rooftop HVAC put out a strange smell for the last three summers- only with the AC on, not in the winter with the furnace running. Techs came out to inspect and clean the unit two or three times with no change. I've read up on Dirty Sock Syndrome, etc- but it doesn't seem the same. The smell is not musty so much as dusty, but with a distinct odor I can't put my finger on. It also is slightly irritating to my eyes and sinuses but I've put up with it rather than sweat through the long hot summers hereabouts.

Old York unit finally died and my landlord had a new Payne unit installed yesterday. I thought that would certainly take care of the smell, but it's still there. I haven't been using the old AC (or smelling the smell) since last fall, but now we're in our first real heat wave of the year so I fired up the AC on day one and am flabbergasted to be having the same symptom. The landlord would pay for servicing, but as I said, people have come out before and never located the problem.

Is it possible for "Dirty Sock" to set into a new unit within 24 hours? Could it be the ducts or wiring in this old house? It doesn't smell electrical, but I'm grasping at ideas at this point. And if it's in the ducts, then why no smell when the heat is on? Any thoughts? Thanks!

Can you tell me what it smells like I know a lot a about hvac systems

It has to be coming from the ductwork.

Lawnman- the more I smell it, the more I've decided it smells like Hot Attic Crawlspace :) I'm inclined to agree with Joshdta that it must be the ductwork, but I'm still mystified as to why it's only with the AC on- maybe it's really about how hot it is in the attic at the time. I'll get someone to look at it again but focus on the ducts- thanks!