I have a 98 Civic, and when i turn the a/c or heater on there a bad smell coming from the vents, does anybody know what might be the problem? Water in the heater or in the canals somewhere?

 

welcome to the forum: Your a/c condensor is dirty with mildew, check to see if when your a/c is on, that the drain is not plugged, and dripping condense water freely. Also can spray Lysol into the intake side of the air intake below your windshield to help kill the mildew and sanitize the air coming in.