Possible overheating, but I'm not sure

Hi,
My car is a 2000 Beetle with 102k miles.
Yesterday while driving at low speeds I noticed warm air seeping out from b ehind the dashboard. For example, if I put my hand near the headlight switc
h, I could feel warm air coming from behind it. I turned on the fan and it immediately started blasting fairly hot air out of the vents, even though t he temperature control was dialed all the way to the left. I kept the fan r unning until I got home, at which point the air was almost a normal tempera ture again. (It's about 75 degrees outside where I live).
I checked the coolant and oil levels, which are both normal. At no point di d any temperature warning light or check engine light appear on the dashboa rd.
Could my car be overheating in some way that isn't being detected? Is it po ssible that the sensor which detects overheating is broken? Or is there som e other explanation for the warm air?
I'm aware that the water pump fails frequently on old Volkswagens. Mine fai led four years ago, and I had it replaced (at a dealership). I did get warn ing lights at that time.
Thanks for any help or advice.
Frank
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