I was driving the car earlier with a/c on, all was well. I parked it for about 45 minutes then got in, started it up, and even though the hvac setting was set to off, fairly hot heat began to blow out of the vents.

At first I thought it was just a bit of accumulation of hot air in the vents but it wasn't. It just kept coming.

I pushed the 'off' button again to make sure it was fully depressed but.... still more heat came out. I put it in a/c mode and it was heat.

This went on for about 15 minutes until I noticed the middle fan speed button was ejected too far out so maybe the low and middle button were in the on position at the same time. I fully depressed the middle fan button and shortly thereafter all was well. But I think it'd be weird for a fan speed button to make the hvac put out heat instead of ambient air or a/c air.

Any thoughts on this?

1991 300d, 222k