If the only way you can keep warm while driving your Corvette in the winter is to wear a ski parka and thermal blankets, then you definitely need to replace your heater core. When you were driving around in the nice summer weather, you never thought about the heater. Now that the temperature has fallen, it would be great to have some heat inside of the car. Replacing the heater core and rebuilding the heater box is not difficult, it is time consuming. You will not need any special tools to accomplish the task, but you will need some patience and the right parts. Our Project 77’s heater core decided to start to leak so we contacted Zip Corvette Parts, 8067 Fast Lane, Mechanicsville, VA 23111, (800) 962-9632, They were able to supply us with all the needed parts to replace the heater core and totally rebuild our heater box. This project will take the average home restorer about 6 hours to complete. It will also help to have an extra pair of hands so try to enlist the help of a friend, wife or girlfriend. Explaining to them how nice it will be to have heat inside of the car usually is a good incentive. Now let’s get started putting the heat back in the car.
Click on the images for expanded views – it’s much easier on the eyes.
01: Is this the only way you can keep warm in the winter while driving your Corvette?
02: Here are all of the items Zip Products sent to complete our project: Heater Core, Heater Box Rebuild Kit, A/C Air Deflectors and Gaskets, mounting nuts, heater resistor. Not shown: A/C water shut-off valve, hose clamps and heater hoses. You will also need some regular hand tools, anti-freeze, strip caulking, an extra pair of hands and a shop manual for your year Corvette.
03: Start by disconnecting your battery. The doors are going to be open for quite some time. Now open the radiator petcock and drain all of the coolant out and into an acceptable container. Remember to dispose of the old coolant in an appropriate manner. Most service stations and auto parts stores will take the used anti-freeze. After the system is drained, remove the heater hoses and clamps. Since you will replace the hoses, use a utility knife or single edge razor blade to slit the hose at the fitting. This will allow you to easily slide the hose off. Don’t forget to go under the car and remove the heater hoses from the core support.
04: Remove the A/C water shut off valve. I recommend replacing this valve. They have a tendency to corrode and freeze up internally which will cause poor operation of your heater and A/C.
05: After all the hoses are removed, go inside the car and start the disassembly. Remove the right lower dash panel.
06: Remove the lower side console panels and loosen the center gauge cluster. You will not have to disconnect and remove this but you will have to move it back and lay it on top of the center console. Place a towel under the gauge cluster so that you do not scratch the console.
07: You can now remove the duct work. Start by removing the right lower duct. Then loosen and remove the crossover duct. Also disconnect and remove the driver’s side lower duct.
08: The courtesy light and fresh air duct vacuum line can be disconnected. Make sure you pay close attention to how the vacuum hose is connected to the diaphragm.
09: The heater box can now be loosened by removing the retaining nuts on the firewall.
10:After the retaining nuts are removed, go inside the car and carefully tilt the heater box back toward you. Now carefully remove the cable and retaining clip. Remember to save the retaining clip. You will need it later.
11: The vacuum hose to the heater box diaphragm can be disconnected. Carefully remove the entire heater box assembly. This is sometimes easier said than done. The heater core tubes go down through the lower section of the firewall so you will have to lift up on the box and roll it towards you to remove it. Just take your time and be patient. It will come out, I promise.
12: Lay the heater box on your work bench and start the disassembly. Mark the temperature control cable bracket mounting screws. Then remove it. This way you will be able to place the bracket back in its original position.
13: Now remove the heater core retaining screws and plate. Separate the heater box and mounting plate.
14: The heater core can now be removed from the mounting plate.
15: The heater box and mounting plate can now be thoroughly cleaned. Use 3Ms #08984 General Purpose Adhesive Cleaner to remove all of the strip caulking from the plate.
16: When the heater core mounting plate is clean, place some strip caulking on the area where the heater core will mount. This will make a good seal between the heater core and plate and also stop any movement or squeaks of the heater core.
17: Install the new heater core on the mounting plate. Now replace all of the rubber sealers and metal shield and secure the heater core in the heater box. Also replace the temperature control cable bracket. Use the marks you made on the bracket to re-align it.
18: The heater core to firewall seal can now be glued to the heater box. Any good contact cement or weatherstrip adhesive can be used.
19: Slide the heater core tube seal onto the tubes. Spray some silicone onto the pipes and seal. This will help to slide it into place.
20: Go inside the car and remove any old caulking or sealer that is on the firewall where the heater box mounts. After everything is clean, install the center post sealer strip.
21: You can now re-seal all of the heater and A/C ducts. The Heater Box Rebuild Kit comes with every seal that you will need. Remove the old sponge seals. Clean off all the old adhesive and glue the new seals into place, weatherstrip adhesive or contact cement can be used for this purpose.
22: The heater box can now be re-installed. Work the heater box into place. Make sure the heater core tubes are lined up in their opening and then roll the heater box back into place. Here is where an extra pair of hands is very helpful. Have your helper go under the car (Make sure it is securely supported) and help to guide the heater core tubes into place while you put the heater box in. Don’t get frustrated. It will fit. Sometimes you have to gently persuade the tubes into place, but it will go in.
23: Before you mount the heater box securely, re-connect the A/C-heater diaphragm and the temperature control cable. When these are re-connected, push the heater box up against the firewall and re-install the mounting nuts and screws.
24: After the heater box is securely mounted, re-install the duct work. Start by installing the lower crossover duct from the heater box. It will go back in just like it came out. Again another pair of hands on the driver’s side will help you to guide it into place. When it is in place, screw its mounting bracket to the heater box.
25: Place the defroster duct into place and re-mount it to the dash.
26: You can now re-attach the center console duct.
27: Before you replace the right lower duct, make sure the A/C floor defector and gasket is in place. This always seems to get broken.
28: Re-connect the courtesy light and air inlet diaphragm. Now re-install the right and left lower dash A/C ducts.
29: The Heater Box Rebuild Kit also includes the center gauge cluster A/C deflector strips. When these are installed, the deflectors will stay where they are aimed and the air will come out through the deflector instead of all around it. If your deflector is broken, Zips can supply new ones.
30: Now go out into the engine compartment and connect all of the new heater hoses. Remember to use new hoses and clamps. It is very cheap insurance against leaks.
31: Install the new A/C water shut-off valve. Remember to point this arrow down and connect the valve into the heater core inlet hose. In some years this valve has a bracket. In other years, it floats. Check your shop manual for which is correct.
32: Here is the bulk head connector for the heater box and shut-off valve vacuum hoses. Make sure all of the hoses are good and not disconnected or broken.
33: Connect the vacuum line to the A/C water shut-off valve.
34: With everything connected, fill the system with new antifreeze mixed with water for your area of the Country. Before everything is totally re-assembled, check the heating and A/C system operation. After you are sure all of your connectors are correct, replace the battery cable. Start the engine, set the selector to heat and open the temperature valve to hot. Check the entire system for leaks. When the engine starts to warm up, turn the fan switch on. Check the floor ducts for hot air. Now try the defroster. Adjust the temperature control. See if the temperature changes as you move the lever. Remember to give it time to adjust. If everything is Okay, shut everything off and finish the re-assembly.
35: You can now re-install the center gauge cluster, console lower trim and right lower dash pad. Check the coolant level and top it off as needed. When you are finished, go out and play in the cold with some real Winter Heat.
1968-1982 Corvette Heater Box Rebuild:
How to Rebuild the Corvette Heater Box
Source: Zip Corvette Parts
8067 Fast Lane | Mechanicsville, VA 23111 | (800) 962-9632
Corvette Parts List Related to Article:
Water Shut-Off Valves:
Heater Box Rebuild Kits:
Heater Box Mount Kit:
Hose Clamps Sets:
Air Condition Deflector: