Hello, it's cold and I need some heat in my 1990 Lumina. I do not get any heat to blow whether it's the defrost, vent, blend or heat buttons pressed. When I press the heat button, the fan doesn't blow at all and blows nothing but cold air when the other buttons are pressed. The heater core was replaced about a year ago so I'm guessing that's not the problem and I checked to make sure the floor wasn't wet on the front passenger side. My father told me it was probably time to replace the thermostat. Is that what the problem may be? Thanks in advance!