HVAC = Heating, Ventilation, Air Conditioning

So what is this separate AC that's involved?

The sweet smell could be an indication of a coolant leak, especially if you could smell it more while the AC was running. You should have it inspected by a technician as soon as possible, especially if you live anywhere that requires an AC system.

Thanks for the replies everyone.

I ran my AC for a few hours today and there was initially no sweet smell. I started washing clothes and took a shower then the smell occurred the next time the AC ran. I then turned the AC off. A few hours later my AC starts running on its own for about a minute. I went into my bathroom and noticed a strong odor that smelled like wet dog. I had a window open in my living room during this time, and I had just finished cooking something in the oven. Now I'm trying to determine if my shower, washer or dryer, oven, or an open window are related to the smell. Are there any tests I can perform to determine this? I plan to avoid using these utilities for small periods of time to see if I can identify a relationship between them and the smell.

Is there anyway I can flush out the odor when it occurs? Should I run my HVAC fan until the odor goes away?

@HU-635769065

I've had maintenance inspect the HVAC unit in my apartment and my gas line, but there were no signs of a leak. If there were a leak, would the sweet smell be coming from my vents every time I run my AC? I'm trying to eliminate the possibility that maintenance has missed a hairline fracture when they checked my HVAC equipment.

@dadoes

I have one HVAC. I specified HVAC fan in the title because I know little about this subject, and I wanted to be explicit.

Do you use a fragrant laundry detergent or fabric softener? The sweet smell may be coming from the laundry room. Try not to do a laundry for a few days and see if the odor disappears. If it does, then do a batch of laundry and see if it returns. Perhaps the dryer exhaust is leaking and the AC return is pulling the sweet smelling air into the duct work.

@HU-109265008

The sweet smell could be a coolant leak from your AC unit and you would smell it when the unit is running. I would recommend having a licensed HVAC technician come out, or ask your landlord to call one at their expense. Even a small leak could be very problematic if not stopped.

I found the solution on another website and it worked! A couple of weeks ago I had a sweetish odor coming from my AC vents and I had no idea what it was. I thought it was a freon leak and had my handler replaced $2k. The next day I still had the sweet odor. I researched everything on the Internet. And finally several days later I ran across this solution which worked for me. Each day the odor is getting less and less. It's 95% better now. I am copying and pasting the exact language that I found on the other website. I hope everyone will share this and I hope it works for you.

This is from bobvila.com:

"There is more than one smell described here, but the one most often described is without a doubt hydrogen sulfide. It's a component of sewer gas (along with methane, and other nasty stuff). Some sources say it's non-toxic, but it can cause health problems like migraines. We have had the same problem, and it turned out the the p-trap for a bathtub we don't use had all of its water evaporate. That allowed the gas to collect under our home, which meant the first run of the heater made us sick. All it took to fix it was running the water in that tub. 1. Make sure your toilets have wax rings and the bolts holding them to the floor are tight. 2. Flush your toilets, run the water in your sinks, and run the water in your bathtubs. 3. Flush the gas by pouring bleach down the drain. That should clear it right up. You may want to run your blower with the windows open early in the heater season to clear out any lingering fumes and air that has been trapped since last year."