It is very cold here in NY and i need the heater to work whenever i drive my car... which is not too often(trying to keep in great shape)

Sometimes i turn on the car and the air will turn on accordingly with the different speeds (low, med, hi) but about 90% of hte time it doesnt turn on at all and i have to use the vent to let the engine heat keep me warm, which doesnt really healp to much.

Does anyone know what might be causing this