It amazes myself and others when I ask people if they think whether or not indoor plumbing needs air ventilation to work officially.
They’re shocked when I tell them that the metal pipes sticking out their rooftops are there to let air out of your plumbing to let water and waste run through unrestricted.
Without typical ventilations, clogs can form, or worse yet—sewer gases can leak into your indoor air. P-traps are installed under sinks so a small bit of water sits blocking any odory and toxic sewer gasses from getting out of the plumbing. If the air ventilation hits a snag, inevitably pressure will have to equalize at the drains and sinks themselves, often pulling the water out of the traps that is your barrier against sewer gases. So you get a house that is perpetually full of toxic methane simply because the pipes do not have satisfactory air ventilation. If you have a sink that isn’t in front of a wall, love several kitchen sinks, you have to get by with an air admittance valve underneath the sink; When they function officially they pull in a small amount of indoor air to push the water or waste down the drain. If they break, they let air in from the pipe, essentially creating the methane scenario. Running your cooling system will just recirculate the fumes until you upgrade the broken valve. I was lucky to have an Heating and A/C serviceman who used to be a plumber. When she was servicing my central Heating and A/C system, she noticed the odor and asked about my kitchen sink. In hours she had the problem inspected. After a quick trip to the hardware store, I had my new valve.