Question about heating vs AC air quality

[beema]

My condo has a central Carrier AC and heating unit. The past couple months I mostly have the heat on, and everything is fine. There are occasions however, when I only turn the fan on with the heating switched off, and others when it has become warm enough that I felt the need to switch the AC on.
When using the AC or the fan by itself, I have noticed that the air coming out smells strange (kind of like old paint), and causes me to feel sneezy.
My mind immediately went to there being a mold problem, but I wondered how this would be possible if the air is perfectly fine when the heat is on.
Does this make sense? Could there only be a mold problem with the AC & fan but not the heat? Or is there some other issue here?
Please let me know if I need to post more information.
Thank you

[toocoolforschool]

You probably just need a evaporator coil cleaning or just a maintenance on your system, get a ac company to inspect it and go from there.

[beema]

Okay, thanks. So I shouldn't be too concerned about mold, then?