There's a button that can enable/disable air circulation. If you disable it, you actually allow outside air to comes in and even though you have the climate control off, you can feel a breeze from the AC port (depending on your speed)
So when the fan is on, the heat is running, even if the a/c is switched off? Even when the thermostat is set to a temp that would not trigger heating? I’ve suspected this and have occasionally wondered if there’s a way to run ONLY the fan (get some fresh air from outside). Seems that scenario is a crazy unattainable fantasy?
Sometimes for reasons like this I miss my 1987 Golf.