I have a 93 beretta gt the car heat's up great, but there is like no air flow on anything, (heater, vent, defrost) i've changed the thermostat, the blower motor is working fine, i've got brand new coolent in it, i've changed the control unit, with the one in my 91 gt and it works fine, I don't really want to tear the dash apart to change the heater core if I don't have too, Could the problem be something else? Maybe a vacuum line. Anything would be helpful Thanks.