From everything I've read on here I think I'm on the right track but I'm not sure. 1968 Cutlass Supreme Big Block with air. Took the nuts off the firewall on the engine side, I think there were four then went under the dash and tried to wiggle the box out. It is loose everywhere except on the top by the core, still feels like it's connected, It's solid. Am I missing something? Do you have to remove the whole unit on the firewall because it's got air? I'm afraid to tug and pry to much I sometimes have a tendency to break stuff, not so bad now that I'm an old guy but in my younger days it was a big problem. Really haven't read anything on here that explained it where even I could understand it. Thanks everybody. Gil....

 

There is 1 nut in a very bad place behind the wheel well under the fender.

 

Heater core replacement on the A-body cars has been covered here a lot. As noted, there is one more nut that requires you to remove the inner fender to access.

 

Both fenderwells are out,got 4 nuts off the studs but the top around the heater core outlet still feels fastened, it's solid! I'm almost to the point of taking oldcutlass's advice, something about suitable amount of explosives.

 

OK. Got it figured out. What I didn't realize and I don't know if they did this at the factory or not. The stud that goes thru the firewall next to the heater core outlet had a nut on it then the box on the firewall was installed, then another nut put on it. Had to drop the big AC box on the firewall to get to it. Just letting people know for future heater core replacements. 1968 Cutlass with AC.

 

And I got flack for going around the long way. A little extra time sometimes saves you from pulling your hair out. Glad you got it figured out. Who would have thought? A double nut? The factory guys must have had a chuckle on that one as in, "Wait till they try to change this!"

 

I have done engines and transmissions. I think I will dread the heater core more than the other. I know I am due for one soon.

 

The first time I replaced the heater core back in the 80s I inadvertently neglected to reinstall that one. The next time I did the heater core I was really glad I had forgotten to put it back.