My front windshield defogger does not seem to be working very well. I only get a few small patches of defogging on my windshield nor more than 8 inches diameter. The heater is working fine and the blower motor is running so their is pleny of hot air. Maybe the clear spots are just incidental air being deflected back at the windshield? I have only owned this car for about four months and now that the weather is getting colder and wetter I am seeing this problem. I am not really sure what the three toggle switches are down by the heater controls. One has three arrows in a circle which I am guessing is to recirculate the inside air, another looks like a defrost button (for the rear window?) and the third I'm not sure. I have tried toggling these on and off to no affect. I wonder if there is something wrong in the duct work. I but my hand up by the vents at the base of the windshield and there is no hot air coming out. I can't really discern anything from the electrical schematic in my Chilton's manual other than the heater fan motor. If I don't get this fixed soon I will have to start driving my 69 GMC truck until I do get it fixed (which only gets half the mileage) Can anyone help me?

Thanks!