Ok this is kind of hard to explain. My heater and defroster will blow out cool air 90% of the time, but if I turn off the fan and just put the thermostat a hot the cab warms up from the astro ventaliation. The car in question is my '86 with a 305. I don't know why it is duing this. Plus when I put on the a/c it blows out hot air from outside.