DIY fiberglass heater duct & heater rebuild (Volvo heater valve)

[jsturner]

Thought I'd share my latest project with everyone. Maybe someone will find it useful.

As we all know, the original cardboard duct linking the underhood heater core to the firewall on many of our cars is less than durable. I got my '51 Windsor with a galvanized steel, riveted, duct taped abomination in place of the original duct and I couldn't stand to look at it in the engine compartment (there are a lot of other interesting no-noes in this picture too; see what you can spot):

Unfortunately, replacements are either very expensive or very low quality and sometimes both, so I didn't like that option. I decided to make my own out of fiberglass using the lost foam method. This is where you make the inside shape of the part out of styrofoam, lay up fiberglass on the outside and then melt out the foam core with acetone. More on that further down.

First I needed to get the rest of my heater in working order. My heater control valve under the dash was missing and replacements are expensive and contain 60-year-old rubber, so I did some poking around and it turns out the 1975-91 Volvo 240 uses a very similar valve; in fact it's made by the same manufacturer, Ranco. I decided to see if that would work.

Plenty of old Volvo 240s at Pick-n-Pull, so a valve was easy to find. It's hidden in the driver's footwell behind the plastic cover to the right of the gas pedal. You have to disconnect the heater control cable, two heater hoses, and extract the capillary tube from the adjacent heater duct. The right way to do this is to pull the whole dash out of the car, then separate the halves of the heater box and pull out the capillary tube. I expedited this by breaking the plastic duct around the capillary tube grommet and pulling it out the new hole. Apologies to Volvo enthusiasts.

Back in my garage my Chrysler control cable needed the loop clipped off the end and then it was easily attached to the Volvo control valve:

A couple differences between the original Chrysler valve and the Volvo valve: the pipe/valve assembly is rotated 180 degrees, so the inlet faces away from the direction the control cable comes from. This means either the control cable or the heater hose that connects to the cylinder head must loop around to the far side of the valve. The pipe/valve assy could be uncrimped and installed the other way, but that seemed like an invitation for leaks and my control cable was long enough to make a big 180 degree turn under the glove box. I installed the valve with the short (inlet) pipe facing the cylinder head:

 

I also had to gently bend the inlet pipe away from the firewall to be able to fit a heater hose and clamp on it. I had to cut away some of the firewall sound deadener on the inboard side as well, to get a better angle. The original Chrysler part has longer brass pipes that aren't such a tight fit. I put a tinnerman nut on the firewall and one on the heater valve; one screw is installed from the engine side and one from the interior side, since the pipe blocks access from the outside.

I coiled up the capillary tube (don't kink it!) and stuck it into the interior heater duct through a conveniently damaged area so it will pick up heat:

 

Edited July 10, 2017 by jsturner
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[jsturner]

My heater core and blower fans were ok functionally but all the housings needed some TLC, so I took them apart and cleaned and painted everything. Wired up the defroster and blower fans per the factory wiring diagram. I used Evapo-Rust on the linkages and then clearcoated them. This linkage needs to be adjusted so both dampers in the box have their forward edges touching the heater core when the lever on the dashboard is in the "OFF" position. I added a couple flat washers under the control arms so they wouldn't scrape my pretty paint:

 

 

Next up: the DIY duct. I'd never worked with fiberglass before so I took this really slowly. I bought a 2x4 sheet of 2" foam insulation and some cheapo brushes at a hardware store and fiberglass cloth and resin at Autozone. I cut and glued together the foam and then carved it with a hacksaw blade to shape the duct. This is a very messy process; little bits of foam get everywhere. Tip: use Gorilla Glue. It won't eat the foam and it expands to fill less-than-perfect foam interfaces. I used wood glue and it didn't dry for a week. Make sure your corners are smooth and rounded so the fiberglass cloth can conform to the shape. Test fit about a million times, and when you're satisfied with the fit wrap the outside in packing tape. This keeps the fiberglass resin from going into the pores in the foam and prevents any possible melting of the foam.

 

 

I made a sheetmetal bracket for the firewall end and a rubber seal for the heater core end. The bracket has holes in the flange that mates with the fiberglass duct; the idea is that resin will flow throught the holes and make the bracket integral with the duct. I also pre-drilled the screw holes that will attach it to the firewall, since this will be difficult once it's all one piece.

 

 

The seal is cut out from an old inner tube and also has holes to trap it in the fiberglass. I left and inch or so of rubber hanging off the end of the duct; this should fold inside the duct and seal to the heater core.

 

 

The ends of the rubber are stapled together:

 

 

I applied car wax to the taped surface of the foam blank. Hopefully this will act as a parting compound and make the tape come off easily later. Finally I used a piece of wood as a stand, drilled some holes through it and stuck bamboo skewers though it up into the foam blank. This way the piece stands up by itself while I lay the fiberglass. I also screwed the bracket down to it to hold it in position. I cut my fiberglass into strips, mixed up some resin, and laid on two layers:

 

 

 

Now waiting for it to cure, then I'll melt out the foam and see what happens. Got my fingers crossed.

Edited July 10, 2017 by jsturner
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[fstfish66]

very  clever,,,cant wait to see how you will get the foam  out of the fiberglass mold,,, goood luck

[Joe Flanagan]

Wow, that's some pretty neat work. I can't wait to see how it turns out. I just did this job myself but I bought one of the pre-fab ducts off e-bay. You're right, they're chintzy--just stapled cardboard. But I coated mine with shellac and it seems to have improved it quite a bit. I managed to find the heat control valve somewhere (don't remember anymore) that had the pipes side by side, so it was an easy install. I also went through the same thing with the heater core, the control cable, the housing, etc. My core leaked a little and had to be repaired. Other than that, it all turned out nicely. Good luck with your project and keep us updated.

[casper50]

When you mix acetone an Styrofoam together the foam dissolves completely. Looking nice so far. Good luck.

[Old Ray]

Nice post..............thank you !

[Jerry Roberts]

When you mix acetone an Styrofoam together the foam dissolves completely. Looking nice so far. Good luck.

 I noticed that styrofoam also dissolves quickly in gasoline . 

[DJ194950]

Nice work, especially for your first time! Thanks for the pic documention.

I would like to know how much of a mess the "dissoved" foam makes as it's removed.

Waiting for updates,

Thanks,

Doug

[Jerry Roberts]

Nice work, especially for your first time! Thanks for the pic documention.

I would like to know how much of a mess the "dissoved" foam makes as it's removed.

Waiting for updates,

Thanks,

Doug

 The little bit of foam that I dissolved in gasoline just instantly turned to liquid . I guess you would need to turn in the left over liquid at the hazardous waste dump . 

[DJ194950]

A small amount of dissolved foam residude ok, but what is a small amount? Sure depends on what you started with and the solvent as acetone disappears into the air itself, but what about the leftover?

Gas  I'm sure works, but what about the leftover smell in the heater duct?

 

Just wondering.

 

Doug

[jsturner]

After the resin cured I sanded the rough edges and stray fibers. It's good to do this before removing the foam core because the foam backs up the fiberglass and makes it easier to sand with some force. Then I used a spray bottle to spray acetone on the foam from one end. (I didn't tape up the ends)

 

 

The foam dissolved easily and not much acetone was required. The packing tape, glue, and plastic film that was on some of the foam was untouched and remained in the duct, while most of the foam dripped out with the acetone onto the cardboard I had underneath.  The mess was pretty minimal. Using rubber gloves I pulled out most of the stuff left inside the duct and then peeled out the packing tape liner, which came out in one piece and took all the mess with it. The acetone evaporated and I was left with dry scraps of hard plastic, all that was left of the foam. I think this could probably be thrown away or recycled. Any chemists here?

 

 

The duct came out nice! The inside is smooth and shiny, with no foam or tape left. I think the car wax made it really easy to remove the tape. With two layers of fiberglass it's plenty rigid. I can handle it without worrying much about damaging it. When I tap it with my fingernails it is a bit noisy, so we'll see if it acts like a drum in the car. Might have to put some Dynamat inside on the flatter areas. I don't think smell will be a problem since the acetone evaporates very quickly and the smell of the resin is going away.

 

 

It fits ok; I had to trim the rubber seal a bit and I'll have to put some safety wire around it to actually seal. Definitely need a thick gasket at the firewall since I didn't get the angle quite right. Should work though! Next I'll paint it flat black, hook up the heater hoses, and final install everything.

 

 

Edited July 10, 2017 by jsturner
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[jsturner]

I managed to find the heat control valve somewhere (don't remember anymore) that had the pipes side by side, so it was an easy install.

 

Do you remember if this was from some later model car, something that could be found at the junkyard? If so maybe I'll go back and poke around, see if I can find a closer match to the original.

[Dodgeb4ya]

Thats the best duct repro I have ever seen!

Congratulations on your awesome project and thanks for showing how you did it!

Bob

[P15-D24]

Excellent job and excellent report!  I'm going to move this to the Technical Archives so it will be easier to fine. 

[Frank Elder]

Sierra Hotel!

Congratulations on a job well done!

[DJ194950]

Came out great!

 

Before putting thing inside use some wax remover to get the Parting wax off so it will stick.

 

How about a coat of rubberized undercoating sprayed on the outside to make it black and soundproof it also? Cheap, avail. many sources, and no need to clean the inside.

 

Grad GTK moved it, hopefully easier to find in the future!

 

Best,

 

Doug

[fstfish66]

Came out great!

 

Before putting thing inside use some wax remover to get the Parting wax off so it will stick.

 

How about a coat of rubberized undercoating sprayed on the outside to make it black and soundproof it also? Cheap, avail. many sources, and no need to clean the inside.

 

Grad GTK moved it, hopefully easier to find in the future!

 

Best,

 

Doug

the under coating is a great idea,,

[jsturner]

Finished except for the strap over the duct where it meets the heater box, and some grommets. It doesn't exactly blast hot air but it does get the car warm inside. There's a slight smell of fiberglass resin but I expect that will go away as the resin cures completely. I didn't bother with any sound deadening and I can't hear a difference in noise inside the car. I plan to ditch the dual glasspacks that came on the car in favor of an original-style exhaust system, so maybe I'll hear it when the exhaust is quite.

 

 

Edited July 10, 2017 by jsturner
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[fstfish66]

really looks factory,, congrats,, maybe  spray  some air  freshener  or  soem thing in the duct to  kill the smelll,,,