1977 Oldsmobile heater core

I had heater problems on my car and it turned out to be the heater core was pluged up with dust and oil, I just blasted it with brake cleaner and all the sudden I had great heat. The easiest way to access your heater core to check this is to take the 4 or 5 screws holding on the heater blower motor on, under your hood and pull the fan out and you should be able to feel the core and tell if it is clogged up.
I am not famillar with you car model but if the motor is accessed under the hood.
The only other problem is you have vacuum lines under your dash that are leaking, off, or your vacuum diapham accuators are not working right, but I would try my first suggestion, first. Thanks