1968-1982 Corvette Heater Box Rebuild

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Posted April 5, 2016 by Zip Corvette in Corvette Technical Articles
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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. 
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Step 1

01: Is this the only way you can keep warm in the winter while driving your Corvette?
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Step 2

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.
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Step 3

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.
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Step 4

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.
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Step 5

05: After all the hoses are removed, go inside the car and start the disassembly.  Remove the right lower dash panel.
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Step 6

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.
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Step 7

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.
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Step 8

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.
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Step 9

09: The heater box can now be loosened by removing the retaining nuts on the firewall.
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Step 10

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.
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Step 11

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.
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Step 12

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.
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Step 13

13: Now remove the heater core retaining screws and plate.  Separate the heater box and mounting plate.
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Step 14

14: The heater core can now be removed from the mounting plate.
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Step 15

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.
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Step 16

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.
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Step 17

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.
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Step 18

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.
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Step 19

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.
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Step 20

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.
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Step 21

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.
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Step 22

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.
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Step 23

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.
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Step 24

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.
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Step 25

25: Place the defroster duct into place and re-mount it to the dash.
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Step 26

26: You can now re-attach the center console duct.
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Step 27

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.
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Step 28

28: Re-connect the courtesy light and air inlet diaphragm.  Now re-install the right and left lower dash A/C ducts.
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Step 29

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.
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Step 30

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.
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Step 31

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.
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Step 32

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.
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Step 33

33: Connect the vacuum line to the A/C water shut-off valve.
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Step 34

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.
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Step 35

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


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Zip Corvette


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