oven hood

We have a range master oven cooker hood that has an extractor fan venting outside. I have confirmed there is no blockage in the ducting to the outside and I have made sure the ducting is fully secure to the top of the hood exit hole. But for some reason the fan seems to be partially blowing...

Hi. We had new oven hood installed. I have notice when I'm cooking the wall behind the oven next to oven hood is wet. Is this normal??