Useless Exhaust Fan

MH1170XS, Large beautiful unit,with 3 noisy fan settings. I noticed that even with the fan at the highest setting, when cooking, all the steam from the cooktop is rising on to my new cabinets. I called Whirlpool and a tech was sent out. He is a contracted employee, not working for Whirlpool. He agreed that the exhaust was useless, but if you cover the vent completely with a piece of paper, it stays covering the vent. That he said was all it had to do. If you pulled the paper from the vent just a little, it completely falls off. When I called Whirlpool back, they said that no warranty is implied as to how well it works. They pointed out that I should have researched this first. No help. I never had this problem with any other Whirlpool microwave (I've bought 3 different ones in the past 3 years for different properties. I will not buy their appliances again due to their snub attitude. I had a minor problem with a KitchenAid stove top, and Kitchen Aid did everything to fix it, above and beyond my expectations.