The vent fan does not draw air from stovetop
The fan does not draw steam and other vapors from the serface cooking underneath. there is lots of air flowing out through the vent duct from the outside wall. there is plenty of air being drawn in from "Active Vent" at the top of the microwave. condensation is building up on the front microwave door when cooking on the surface below.
Microwave Ovens - GE - JVM2070 Microwave Oven
Answers & Comments
There is a wire mesh filter and a carbon filter on the under side of the unit. IF they are plugged then it wont draw air. The other issue is this unit has a dual option for installing the fan. One is to vent to the outside and the other is to vent to the inside, if the fan is not installed for the correct usage, you have no airflow either.