help please

hello everyone im at a point now were im stuck. i have a 77 280z and when the laft turn signal is on it blinks and then i hear what i believe is a vacuum leak, and when i turn my heater lever from ac to heat it doesnt blow hot air? i know the heater core is getting warm coolant. is there a door that covers the heater core keeping it from blowing? and if so how do i access that to get it open? we just got a foot of snow and its cold as crap so id like a heater. any help would be appreciated thanks.