A/C Heater Box Restoration Made Easy

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I've been working on this slowly for quite a while now and finally finished it (GTX beat me to it half way through). Hopefully you guys will get some use out of it. This is my heater box restoration. I'm not an expert (but I did stay at a Holiday Inn once) so if anyone sees anything I've done wrong with this please let me know so I can correct it, it is only a guide.

Unfortunately I didn't take many detailed photos overall during disassembly, so I'll start with the reassembly once I had all the parts cleaned, painted and ready for assembly. I had my hardware sent off to be re-plated and knew they would throw everything in one pile. I took quite a few photos of the screws and the screw locations during disassembly. I also took a few labeled photos of the screws themselves so I knew exactly what each screw/nut looked like and where it came from. It's also a good idea incase something goes missing that you'll know exactly what it is. I also took photos of the order in which the linkages came off so I could put it back on the same way. I would also test the vacuum pots to make sure they work and don't leak before you spend the time to clean them up. Another point (as also mentioned by GTX) is to take care when removing the evaporator drain tube ferrules from the drain tubes which are copper, they can be a real pain so take your time and go easy on them.

I probably went a bit overboard and had everything chemically dipped, repainted and re-plated. I also had the heater core and evaporator tested before hand to ensure they wouldn't leak. I also took my blower motor apart and serviced it, and, after destroying one motor I can pass on my mistake to save someone else the same trouble. I can post this later if anyone is interested in servicing your motor.

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On to Assembly,

I purchased the complete DMT heater box kit which has just about everything you'll need to restore your heater box. Although the kit includes some hardware (clamps, push on retainers, a small cotter pin and some mounting nuts) the only things that would make the kit better in my opinion is if they included better instructions and the springs that have gone missing over the years. The molded blower motor gasket and rubber insulators would be a nice addition too as they tend to perish and need replacing. The DMT kit tells you to use a high-strength high-temp solvent free adhesive, I found this to be nearly impossible as all the "good" adhesives contain a solvent. These are the two I bought, 3M #90 High-Strength and Super 77 which is safe for foam. I've tested the #90 on all of the different offcut materials and it's safe to use on all foam EXCEPT the white polystyrene, use the Super 77 for these pieces. Save the offcuts until you finish the box incase you damage some of the insulation while rebuilding the box.

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First off, go around the heater box case and seal all of the seams with a high temp sealer. I found the inlet neck from the blower fan the worst, especially in the corners. Test fit each piece of insulation for fit and proper alignment before gluing it down. They tell you to use spray adhesive but I feel that a brush on version would be much easier to work with and less messy then the spray.

I started with the back of the box first using the 3M #90 to glue the black matted fiberglass down. The back piece fits under a few metal tabs so installing it wet will allow you  to slide it around and make it much easier to put in place.

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You need to glue a piece of insulation to the top of the A/C Evaporator. The A/C evaporator attaches to the drip tray with four small 1/4" coarse thread screws in the locations shown. Lastly don't forget to put the seals on the drain tubes. It is now ready to be installed in the box.

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The evaporator assembly should slide completely into the box fairly easily and is held in with six small 1/4" coarse threaded screws. It went in much easier then it came out. I then installed the foam rubber firewall seal on the outside of the box and also put the blower motor firewall seal in place at this time.

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Install the main front door flapper rod into the front half of the box first before gluing in the white foam. It is not shown installed but it is the shorter of the two rods. I installed the rod after which wasn't a good idea, hence why I suggest installing it first. I damaged the foam slightly and had to use an offcut to patch it. The rod is held in by one e-clip. Next, I glued down the white insulation in the front half of the box using the 3M Super 77. The glue sticks extremely well so have some thinners on hand incase you get it on your fingers, or you'll find yourself sticking to everything. Try not to get any glue on the edges of the pieces, if you do it will make handling them difficult. Lastly, install the longer bottom flapper door rod into the front box half using two e-clips, one on each end.

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The flapper doors are quite easy. The DMT kit gives you two long foam strips and a precut foam piece for these. The longer of the two foam strips gets cut into 3 pieces and stuck to the sides and bottom on the front side of the door. The shorter strip gets stuck to the bottom edge on the back side of the door. The pre cut foam piece gets glued to the back side of the main heater box door. Double check that your correct before you stick them down as it's easy to stick them onto the wrong side. The longer lower flapper door can now be attached to the flapper door rod using 3 of the 1/4' fine thread screws. The main front door can be set aside and installed later. Double check that the flapper door operates freely and make sure that the flapper door seals make good contact to the surfaces they are intended to. I had to bend one of the tabs back slightly as it was bent, and also tweak the door slightly for a good fit. It's the little details that make the box more efficient and work better. 

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For the intake box you need to glue in three pieces of black matted fiberglass with #90 adhesive followed by the foam for both sides of the door. The foam for the doors is not square so make sure you orient it correctly before gluing it down. Gluing them down can also be tricky, the best way I found is to;

1. Keep it off your fingers, or you'll be cussing up a storm or worse yet damage the foam.

2. Quickly spray about a 1/3rd section of the door itself and the foam seal that is closest to the pivot rod.

3. Quickly install the foam wet so you can slide it around into place for proper alignment and let tack up.

4. Gently pull back the un-glued portion of foam and spray the remainder of the door/foam and stick together.

Be careful not to over saturate the foam with glue or the foam will dry in a compressed state when you stick it back down. Do the same for the other side. Open and close the door a few times just to make sure everything operates as it should without fouling. Trim if need be. Next, glue the large 6 1/2" foam ring to the outside intake box. You'll also find 3 small foam rings in the DMT kit. Two of these are identical and one is slightly thinner. The thinner one (pictured on left) gets glued to the time delay valve that bolts to the bottom of the intake box. The other two are for the defroster outlet doors which we will use later. Put the time delay aside for now and install it later so it doesn't get damaged. Now bolt the intake box to the main heater box body with four 1/4" coarse thread screws.

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All of the heater core seals are included in the kit along with hose clamps and hoses for the "h" valve as well as strip caulking. It would be wise to purchase an extra roll of caulk incase you need it. During disassembly pay close attention to the core as you pull it out and note/mark where the strip caulking was from the factory. The person who attacked my heater box before myself replaced the core, but unfortunately didn't bother to install any seals whatsoever. My core was an aftermarket replacement so the vertical foam strips didn't quite line up properly with the condenser to begin with. I had to cut a chamfer into the foam strips to move them inward slightly so they would seal properly, it was still marginal at best so I also ran a strip of caulk up the inside of the vertical foam strips. Because my core was an aftermarket core it had more holes then a piece of Swiss cheese. This is when that extra roll of caulk comes in handy. I had to use a fair bit of caulking to fill the gaping holes in the corners and run caulk along many of the edges.

I quickly tested the "h" valve before installing it by blowing into it while blocking off one of the legs. I operated the valve a couple of times while blowing into it to see if it was sealing, it did so I reused it, plus it didn't look that old. Next I attached the "h" valve with the supplied hoses and clamps. Take care when installing the o-rings into the grooves on the pipes that you do not knick or cut them. Check the tubes for burrs and clean them up if they are rough. Also, make sure the o-rings aren't twisted in the grooves after you install them, a bit of o-ring lube will help settle them in easier. Make sure you use a petroleum free O-ring lube. I then attached the large foam strip onto front side using 3M #90 adhesive.  

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Now it's time to sandwich the core between the two halves of the box. You need to run a strip of caulking up along the left side, across the top, and back down the right side edge of the back side of the core. I found it easier however and more precise to stick the caulking directly to the back half of the heater box instead of  sticking it to the core. Now is a good time to lightly lube the o-rings if you haven't already as it's nearly impossible to do so once the box halves are bolted together. This will aid in joining the copper extension tubes later.

Now slip the core firmly into place being careful not to dislodge the caulking, press/squeeze it together quite hard all the way around. Once the core is firmly seated in place it wont move. Now we need to install some caulking to the front half of the case in same manner as the back half. Once you are happy with it it's time to put the front half on. You'll have to sort of gently roll it on from the top edge making sure the studs from the back half pass through the holes in the front half. Be careful not to dislodge the caulking. Once on properly press/squeeze the case halves together firmly so they seat properly, then bolt the case together. Loosely install the 2 screws that hold the "h" valve to the front of the case, we will tighten these later.

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We need to hook up the "h" valve linkage, one end gets hooked into the "h" valve arm while the other end gets screwed to the flapper rod with a fine thread 1/4" screw. Operate the flapper a few times and verify that the "h" valve is working properly. Now it's time to glue the gasket to the copper extension tubes mounting flange, be careful not to get any glue inside the brass fittings. Lightly lube the insides of the brass fittings with a thin film and slip the tubes into place, now bolt them down with four 1/4" coarse thread screws. Tighten the "h" valve screws.

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Next I Installed the defroster flapper rod and doors and secured it with an e-clip on the end.  Screw the doors down with four 1/4" fine thread screws but leave them slightly loose so you adjust them a bit for better alignment. Mark the top of the door closest to the copper tubes, it is a good idea to remove this door the very first time you run the car so you can see if there are any leaks. Or if you have the equipment you can pressurize the cooling system without running the car. I then installed the main door with two 1/4" fine thread screws. Next I installed the blower motor resistor with two 1/4" coarse thread screws and attached the hose routing clips with 2 more 1/4" coarse thread screws.   

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I'm quite happy with the way the blower fan assembly turned out, it far exceeded my expectations. If I were to do it again though I'd probably paint the motor silver which I believe is correct. Again, the previous owner replaced the motor at some stage but still managed to get everything wrong. I had to figure out how it all went back together properly. The only gasket that wasn't included in the DMT kit is the molded blower fan gasket. Take special care not to damage it. I washed it in warm soapy water then dried it off. I then treated it with "303 Aerospace Protectant" which is a silicon free product. It rejuvenated the rubber quite well.

The order in which the fan assembly gets assembled is the flanged mounting ring, rubber gasket and then the flat mounting ring. Now sandwich them all together and bolt them on one side of the rubber insulators, don't over tighten them. Next, install the blower motor on the opposite side of the rubber insulators making sure the vent hole is in the correct location.

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Lastly, install the fan, spring clamp and the vent tube. It is now ready to install in the heater box with three 1/4" coarse thread screws. We will install it after the linkages and vacuum pods.

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On to the linkages. I first connected the long vacuum pod with the push nut onto the linkages (thanks to GTX's advice). Next I installed the vacuum pod bracket onto the heater box, leave the two nuts slightly loose so you can adjust the bracket when installing the pod. Put the spacer on the longer end of the flapper rod. After loosely installing the pod with linkages attached, I pushed the thin rocker from the linkage on followed by the triangle lever for the main door, defroster rocker, and then the large rocker.

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With the spring attached to the small rocker and the small lever, install it and retain with the proper nut. Tighten all of the flapper rod nuts with the flapper doors in the same positions as in your photos, now tighten down the pod. I then installed the short pod with the tiny cotter pin followed by the intake box door pod.

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Install the blower motor with three 1/4" coarse thread screws. Tap the condenser drain tube ferrules on followed by the drain tube firewall seals. Next I chose to glue the fiberglass firewall insulation to the box. Put the steel washers onto the heater box studs followed by the white gaskets. Connect the vacuum lines and you're done, it's ready to be installed in the car.

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Once it's in the car you can attach the intake hose, outlet, thermocouple, time delay valve, dash strap etc...  

Ok, I'm done.

[DC_1]

Well played 440....well played!

[tan top]

 nice job    thanks for posting the pictures 

[Hemidog]

Ah, this takes me back two years.....
Looks very good! 

[Hemidog]

double post

[CDN72SE]

Very nice and thanks for posting, I keep looking at mine lying on my basement floor waiting for my attention.

[Dino]

Excellent work my friend!   

[jdiesel33]

This is awesome. Thanks for posting.

I have mine all apart right now. How can you test the core and evaporator to see if they are still good or need to be replaced?

Thanks
Jim