Betsy, you need to know is it because the fan isnt blowing, or is the water supply to the heater not flowing. under the hood on the passenger side you have 2 larger hoses going into the area you sit. one is a inbound supply the other is the returning supply to the engine. this water is sent by the water pump through a by pass system around the thermostat that way you get faster heat and more consistant temps. your car has a valve that those hoses have in line that controls just how much you send into the seating area (passenger compartment) this valve often goes bad and causes no heat when winter comes on since its often not used durring the summer. hope this was helpful, I have a free web site www.mycarandineedhelp.com just for helping people this way.