OK, took it to dealer and had it pressure tested. They say it's fine with no leaks

I know it leaks a very small amount, and does it sometimes under the following circumstances.

I start the car, run the AC (car has ACC) car gets cold enough that I bump up the temp guage a notch, or three. shortly thereafter strong wiff of coolant smell out of the vents, and then it fades away.

they had the car all day with this description and didn't really check the description of symptoms. (though they say they also visually inspected the heater core)

has anyone else had a similar problem?

if so what was it?