when cooking with a pro-convection oven what is the difference between the High fan settng and the low?

Answer 1

I believe the low fan is for slow or slower cooking and high for faster and higher temp cooking

Answer 2

Sometimes the high fan setting is too drying, and the surface of whatever you're cooking could get brown or too crispy before the dish is cooked in the center. So if your cookies get too brown on the outside while the center stays doughy, try the slower fan, and/or lower the oven temp.