I can smell fuel and plastic odors when I turn on the heater fan in the car lately. on 1997 Mercury Villager

Lately, whenever I turn on the heater in the car , I can smell a fuel odor. I had to open the window on the passenger side in order to continue driiving to my destination.

Asked by for the 1997 Mercury Villager
Check your gas cap 1st,If that is tight.These cars had recalls on the gas vent hose.They have also had issues with the small hose between the fuel rails leaking.Turning on the heater is just bring the fumes in to the car it is not the source of the smell.