Answer first, context after
Why does my AC smell weird?
Match the smell: musty means a damp coil or clogged condensate drain, dusty-burning on first startup is normal for an hour, ongoing electrical or burning smells mean shut it down and call, and anything like rotten eggs is a gas issue: leave first, then call the gas company, then us.
Smells are diagnostics you can run yourself, so here’s the field guide, sorted from harmless to leave-the-house.
Musty, like a wet towel. The most common one. Your evaporator coil lives cold and damp in the dark, and its drain pan and condensate line grow things when neglected. The smell rides the airflow into every room. The fix chain: check the condensate drain first, then coil cleaning, which is part of every Bloom Plan visit. If mustiness persists after both, we look deeper at the duct side, because return leaks can pull crawlspace air into the system.
Dusty burning on the season’s first heat. Normal for the first hour: it’s the summer’s dust cooking off the heat exchanger. If it’s still going the next day, or it’s happening on cooling, different story, see below.
Electrical, acrid, or ongoing burning. Not normal, not a wait-and-see. Overheating motors and failing wiring announce themselves this way. Shut the system off at the thermostat and call; motor and electrical repairs are ordinary flat-rate work, and catching them at the smell stage is dramatically cheaper than at the smoke stage.
Rotten eggs. That’s the odorant added to natural gas so you can smell danger. Leave the house first, then call the gas utility and 911 from outside, then us. No HVAC visit outranks that order, and we mean it.
Sweet or chemical. Possible refrigerant leak. It won’t hurt you at typical household exposure, but the system is bleeding capacity and money; that’s a diagnostic call at the usual $89, waived with the repair.
Still stuck? That's what the truck is for.
The diagnostic is $89, waived when you book the repair, with a written flat price before any work starts.