Here's a general outline of the process, understanding this is a *simplified* overview and you'll need a detailed repair manual specific to your 1979 Trans Am:
Before You Begin:
* Consult a Repair Manual: A Haynes or Chilton manual for your specific year and model is crucial. This will provide detailed instructions, diagrams, and torque specifications.
* Gather Tools: You'll need a wide variety of tools, including various sockets, wrenches, screwdrivers (Phillips and flathead), pliers, a drain pan, coolant flush, and possibly specialized tools for accessing specific fasteners.
* Safety First: Wear safety glasses, gloves, and appropriate clothing. Work in a well-ventilated area. Coolant is toxic.
General Steps (Assuming Fender Removal):
1. Drain the Cooling System: Completely drain the coolant from the engine and radiator.
2. Disconnect Battery: Disconnect the negative terminal of the battery.
3. Remove the Fender: This is the most labor-intensive part. You'll need to disconnect various components connected to the fender, including wiring harnesses, lights, and possibly other parts depending on your specific model. This involves numerous bolts and fasteners.
4. Access the Heater Core: With the fender removed, you'll have much better access to the heater core housing located behind the dash. This often involves removing parts of the dashboard and possibly the glove box.
5. Disconnect Heater Core Hoses: Carefully disconnect the heater core hoses, having a catch pan ready to collect any remaining coolant.
6. Remove the Heater Core Housing: This may involve removing several bolts and carefully maneuvering the housing out.
7. Remove the Old Heater Core: This can be tricky. Sometimes the core is simply clipped in, other times it may require more force or specialized tools.
8. Install the New Heater Core: Carefully install the new heater core, ensuring it's properly seated and aligned.
9. Reassemble the Heater Core Housing: Put everything back in place, ensuring all fasteners are tightened to the correct specifications.
10. Reconnect Heater Core Hoses: Reconnect the heater core hoses securely, using new hose clamps if necessary.
11. Reinstall the Fender: Carefully reinstall the fender, reconnecting all wiring and other components.
12. Refill and Bleed the Cooling System: Refill the cooling system with the correct type of coolant and bleed the system to remove any air pockets.
13. Test the Heater: Run the engine and test the heater to ensure it's working correctly.
Why Fender Removal is Often Necessary:
The heater core is typically nestled deep within the firewall and is very difficult to access without removing the fender. The limited space behind the dash makes maneuvering tools and the heater core itself incredibly challenging.
In short: While technically possible to attempt without fender removal, it's highly discouraged. The time saved will likely be far outweighed by the increased difficulty, potential for damage, and overall frustration. Removing the fender provides the necessary space and visibility to perform the job correctly and efficiently. Invest in a good repair manual and prepare for a multi-day project.
