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NOS, New, Used and Reproduction Cadillac Parts & Accessories for 1961-1991
1965-1968 Cadillac HVAC Casing Seal Installation Guide
Step 1: Be Prepared for anything or everything
Follow the recommended shop manual procedures for removing the HVAC casing from the firewall. Besides the easily visible bolts around the outer edge of the casings, there are some not so easy to see or get to along the bottom. Be sure to find and remove them all as it’s very easy to crack or break the casing by trying to pull it off the firewall and having missed one lower bolt (I’ve seen dozens of casings with the bolt flange just below the center seal broken clean away, cause that bolt was missed during removal).
In addition, check for any wiring/vacuum lines that still might be connected or in the way of removing the casing. Replacing old wiring harnesses or tracing out a ripped vacuum line is no fun so take your time, triple check everything and be sure you’re all clear for removal.
And with any old car system, once removed from the car there may be other uncommon parts you will find needing repair or replacement. It is not unusual for these HVAC casings to have the metal inner framework and air diverter metal fins to be rotted or rusty. You may also find cracked or broken fiberglass on the casings or the casing filled with an insect or rat nest, lovingly built by some friendly neighborhood pests. So, be prepared for these and other possibilities.
Step 2: Assess and Record
Take the time figure out what else you may need to do this job. List anything needing repairs (rotted parts, broken items) or anything needing replacement. You have the whole setup open in front of you so now isn’t the time to cheap out and not replace a heater core of questionable integrity. I personally recommend at bare minimum having both cores boiled out and pressure tested before installation.
And I HIGHLY recommend replacing the air diverter door vacuum mode unit if it’s leaky or completely popped. The only way to access the nuts holding it to the casing is with the heater core casing removed from the firewall to access the nuts.
Make notes and take pictures of everything before taking anything apart. This is so you can have a record of where everything went, places the factory installed sealant/caulk, places that look like they need caulk etc.
Step 3: Disassembly, Cleaning & Seal installation
Once you’re at the point where you have everything required to do the job, you can start removal of any old caulking sealant, rubber seals and dried out foam. The majority of the internal sealing is done with the strip caulk except for the heater core seal and air diverter door.
Heater Core Casing Section 1
Start with removing the heater core frame assembly, held in with 4 screws. Removing the screws and pulling core assembly will give you unrestricted access to the air door. The air diverter door is in the heater core half of the casing, controlled by the vacuum mode unit on the side of the casing. Disconnect the door arm from the spring and mode unit. Clean any old foam off the air door as well as any old glue. If the door is very rusty, now would be a good time to sand it down, prime and paint it. With the door surface now smooth, use a small bead of cement around the border of the new foam as well as some in the center portion. Allow the glue a minute to become tacky and then press the foam onto the door, making sure it’s evenly aligned at all sides. Clean up any areas of the framework that had dried up caulk. You can then reassemble the framework in the casing, using new strip caulk where originally placed.
Remove the old heater core, cleaning up any old, dried up caulking along the core support frame and placing fresh caulk in the channels. Remove the old rubber heater core pipe grommets and replace them with the new ones. They are 2 different sizes with inside diameters corresponding to which pipe passes through them. These new grommets will fit VERY tightly in the original holes and take a bit of effort to get in. This is intentional so there is no air gap around the opening and to put more tension on the rubber around the inlet/outlet pipes. Once installed, reinstall the heater core to the metal framework and bolt back into the casing.
Heater Core Casing Section 2
Next portion of this casing section is the main surround seal. Clean all residue from old glue, seal bits, dirt, etc from the surround flange. Test fit the new seal before gluing so you can visualize how it will install. Remove the seal and apply a thin bead of cement along the center of the casing flange all the way around the case and install the new seal while still wet, sliding all the sections back and forth a bit to spread the cement under the seal before centering the seal on the flange and applying pressure. This is simply to keep the seal in place and aligned for final installation of the casing to the firewall later, so you don’t need to use a large amount of cement.
Lastly, remove the power servo if you haven’t already. Remove the flange seal and edge seal from the servo and clean away any glue or foam residue. With both sections clean, cement the new foam seals in place and allow to set before reinstalling the servo to the casing. With the servo installed, take the small round foam seal with the half split in it, slide it onto the air mix door rod at the top of the casing and then down into the hole surrounding the rod, half the height of the seal. The split side should be facing towards the engine bay, not the firewall. The rod will pivot freely and the foam seal should stay in place. NOTE: if the rod is rusty, it should be cleaned to bare metal and greased so the seal doesn’t get ripped up.
Evaporator Core / Blower Casing Section 1
Start by removing the evaporator core half casing from the main casing body. You’ll notice the 2 halves were sealed with strip caulk, not a rubber seal.
On the lower portion of the smaller casing, you’ll find the drain port for the evaporator core housing, which may or may not still have the old rubber drain tube on it. Remove any old remains, clean the port in and out and install the new rubber drain tube with the included spring clamp. This is a specially design tube to allow water to drain out, but keep outside air, debris or pests from getting in. On the right side you’ll find the curve flange that mates to the heater core side of the HVAC housing. Remove any remains of that seal, clean the flange and make a light mark with a paint pen on the center of both the flange arch and seal, which will help greatly with alignment. On some casings, there is a raised line mark, indicating the center line of the seal flange on the case. apply a light coat of the contact cement to the flange and the flange seal. Once the cement is tacky, start with the center of the seal on the center of the flange and work your way down each side of the arch, applying light pressure.
Evaporator Core / Blower Casing Section 2
Moving to the main casing, remove the blower motor and evaporator core from the housing. The original evaporator core to casing seal was sometimes just caulk and sometimes a rubber seal, depending on if the core was ever replaced. Either way, clean out the seal channel, apply some cement to the new foam rubber seal and gently press into the channel. Use the strip caulking to seal any gaps between the metal air fins and the casing. When reinstalling the blower motor, use strip caulking around the opening in the casing, press the motor flange onto the caulk and bolt back down. Reinstall the evaporator core and then use strip caulk in the channel where the two core casing halves bolt together and reassemble the halves. Next, press the 2 foam core pipe seals into position around the evaporator piping protruding from the case. Lastly, using the contact cement, apply the cement to the casing flange all the way around and position the main casing seal onto the flange, sliding it back and forth a bit before centering the seal on the flange and lightly pressing it down all the way around the flange. Some areas like the blower motor surround, the seal doesn’t press into the channel groove but merely sits on the channel walls. Once the casing is bolted to the firewall, the seal compresses and fills the channel groove, sealing it to the wall.
Step 4: Final Check & Mounting
Perform a final examination of everything you done. Make sure everything is still in the correct position and hasn’t shifted, anything else that required repair or replacement is done and all moving parts function freely with no sticking or binding. If all is good, you’re ready to mount the casings back to the firewall.
Start with the blower/evaporator portion, installing all the firewall bolts thru the flange holes and tightening them down just to the point where the seal sits against the firewall BUT is not compressed. Do the same for the heater core casing. Once both sections are mounted, go around the flanges tightening the bolts enough to compress the seal firmly and evenly but not crush the casing to the firewall. once everything is back together and running, you should notice a difference in air flow into the cabin as well as air quality into the cabin (less engine bay fumes, moldy smells, etc)
Everything mentioned in these instructions are simply recommendations and by no means the only way to install the kit. Feel free to use other sealing methods (tube caulk, other adhesives), adding more sealant to other areas as you deem necessary or reinstalling parts back onto the casings once it is remounted.