77ricbaez

1. You may not need to drain the radiator if you’ve bypassed like I did, if not then it’s a good idea.
2. Disconnect the negative battery cable (you don't really need to actually, just unfasten the connections to the glove box light)
3. From the inside of the car, remove the glove box and glove box door
4. Directly behind the glovebox is an AC distributor and is held in by 3 nuts. First remove the duct tubes from both sides of it (one leading to the passenger side “crotch vent” and the other to the driver side)


the thing on the left is the lower outlet, the thing on the right is the ac manifold

5. Go back out to the engine side and remove the resistor assembly and shine a light down in, you’ll see a nut on a stud, remove the nut (ratchet and socket was easiest)


the resistor assembly is a diamond shaped thing with a plug. It is held by 2 5/16" bolts

6. Remove two more nuts from the upper and lower evaporator case half (one on the top which is hidden by a bunch of wires,be careful, and one directly below it)
7. One more nut by the core tubes, right by the transmission dipstick.


bolt is already removed
8. Go back to the inside of the car, remove a nut on the lower right hand corner of the heater assembly.




9. Remove the lower outlet on the left side


the thing on the left is the lower outlet, the thing on the right is the ac manifold

10. Directly above the outlet is one last nut which bolts on to the defroster duct. Remove the nut.



11. Disconnect the vacuum connections on the diaphragm on the left side



12. Disconnect the temperature control cable (play around with the temperature dial to see which mechanism moves). A small nut secures the cable, take off the nut and slip off the cable
13. The case is now ready to be removed. Work it to the rear until all the studs (on the engine side) clear their holes.
14. With the case out there are two more vacuum lines that need to be disconnected.



15. 3 nuts hold the core assembly in the case, remove them and slide the assembly from the case.
16. There are two different kinds of brackets on each side of the core, each held on by two nuts, remove them.
17. The core can now be separated

INSTALLATION IS REVERSE OF REMOVAL; IT IS A PAIN TO REINSTALL THE ASSEMBLY TO THE FIREWALL.
Tip: Have a helper help line up the core tubes to the entrance. If the defroster duct isnt lined up dont fret. You should try to get all the studs in at the same time along with the tubes (if it came out, it can go back in)
TAPE ANY TORN PADDING
Also when reconnecting the temperature control cable it make sure that the vent door (if you peek through the resistor opening you'll see the door either exposing the heater core or hiding it) is corresponding to the temperature you have selected. For example, if you are on cold then the door should hide the heater core and if you're on hot it should expose it.

Thanks to @76olds for guiding me through!

76olds

This post is awesome!!!

These pictures along with detailed information will help all of us guys with 73-77 year Oldsmobiles.

I'd like to thank-you 77ricbaez for taking the time to assemble the pictures and literature in an easy to view and read form so many can attempt this.

Cheers buddy,
Eric