The heater only works part of the time, sometimes it will blow hot air on one side and cold air on the other side. Sometimes you have to bang on the dash to get anything at all and not all the time will that work. I've already replaced the heating/ac switch unit and that did not fix the problem. Need to know what the problem is, winter is coming and the windows will not defrost so its not only a hazard but I will be unable to drive it for months on end till the weather warms up. Please Help!!!!