Defroster/Heater Switch

I’m restoring an early Heinkel with the air vents in the door and I was missing the heater/de-mister switching piece.  This is a hard to get item, and I’d been looking for a few years to find one. Since I’d been doing all sorts of metal work to fix my car, I thought I had the skills to reproduce my own piece. It took a while but it wasn’t that hard, and the materials were basically free. An enthusiast with a little bit of skill and perseverance could do it, so I’ve made up the instructions below in case anyone else wants to make their own.
Pictures and Drawings:
I didn’t have the piece and didn’t know anyone with one (in the USA there aren’t many Heinkels), so I posted a question on the Facebook Heinkel Trojan Club page. Mark Fisher came up with some pictures for me:

Heinkel Kabines and Scooters
Heinkel De-Mister Photos
It was time to put my 7th grade mechanical drawing skills to work! Based on the one measurement I knew (the pipe opening of 45mm), I could determine the other measurements from the photos and produce a drawing of the most complicated parts. Here are my drawings of the main pieces for your reference (I’ve simplified a few things based on the materials and tools available):  
Heinkel Cars and Cabin Scooters
De-Mister Main Tube

Heinkel Cars and Cabin Scooters
De-Mister Backing Plate
Materials and Tools Required:
I scavenged most of the materials, and you probably can too. Here’s a list of the materials and tools you need to make the parts:


·         1 foot length of 1 ¾” (45mm) exhaust pipe
·         3” wide steel stock, 1/8” (3mm) thick and about 8” long
·         4” length of ¼” (6mm) smooth steel rod- zinc plated if available
·         2 rubber grommets that fit around the rod
·         3mm screw and washer

If you are restoring a car you probably have most of the tools you need:

·         Drill press or cordless drill with vise
·         1 ¾” (45mm) bi-metal hole saw
·         8mm drill bit
·         1/8” (3mm) drill bit
·         3mm tap
·         Angle grinder with cutoff wheel, grinding wheel, and 40, 80, and 120 grit flap disks
·         Pipe center finder
·         Welder

Once you have the parts and the tools you are ready to go. There are five metal pieces you will need to make:
  • Backing plate
  • Main Tube
  • Heater nozzle tube
  • Air deflector
  • Valve

Let’s walk through each one:

The Backing Plate:
This piece attaches to the car body and sits snug against the door when it’s closed. The original piece was stamped; since I don’t have a metal press I substituted 1/8” thick steel stock. The strength should be more than adequate for the purpose intended.  
This piece requires three different operations; drilling, cutting and bending. Here’s how I did it:
I transferred the drawing to the steel plate and then used a center punch to mark the hole locations. This piece has 3 holes. The largest hole is 45mm (1 ¾”) and can be cut with a bi-metal hole saw. 
Hole Saw

Layout of Backing Plate
After you cut the hole save the little blank, which will probably be stuck up inside the saw; you can use that for the switch piece! The other holes are 8mm (for the door hinge) and a 1/8” (3mm) hole.  
You can drill the big hole by making a small starting hole and then using either a drill press or a cordless drill, provided you can mount the bar stock securely. Use a low speed (I used 625 rpm on my drill press) and some sort of cutting oil or lubricant the keep the temperature down and prevent the heat dulling the tool.
Once I drilled the holes I cut the backing plate to size using a grinder and cutoff wheel. It’s crude but effective. Once I got the approximate shape I used a 40 grit flap disk to get close to final shape, followed by 80 and 120 flap disks to finish it up.
Bending a 3mm thick steel plate is not easy! I put it in my vise and used an 8 pound sledgehammer to get the angle to 45 degrees.

The Tubes:

You need to make 2 tubes; the main tube and the heater diverter. The diverter tube needs to be scribed to fit the main tube. Before the internet, determining how to do this was tricky; now all you have to do is go to a website, enter some calculations, and voila you have exactly what you need. I use the website produce a graph that I then attached to the tube. Once you do that you can cut away the excess metal with a standard 36 grit grinding wheel attached to your grinder. 
Graph wrapped Around Tube

You can also cut the diverter tube to length with a hacksaw or cutoff wheel, then sand the cut smooth. I made mine about 5mm longer than my estimate because it looked a little short.
The main tube requires several operations. The first is to cut the tube at an angle for where it will be welded to the base plate. I eyeballed about a 12mm difference in length from the photos that Mark provided. I also knew (or hoped!) that if I was off I could just bend the base plate into a final adjustment. Then I drilled a 45 mm (1 ¾”) receiving hole into the tube using the hole saw. If you have a drill press you should use a center finder to make sure you have the exact middle. If you need a center finder they’re available on the internet for about $8 (6GBP).  They look like this:
A cheap center finder

The last operation on the main tube was to drill holes for the switch part. Once again use the center finder to find the center of the tube, then mark and drill the holes straight through the tube and come out the other side.

The Switch:
Since I didn’t have any information or picture of the switch I had to make it up (of course I found one later!). I decided to put the switch in place past the heater outlet, since most of the time I thought I’d need heat rather than defrost in cold New England.

Remember the blank from the base plate? That is the perfect size for the switch valve. You need to attach the blank to some sort of lever so you can operate the switch. I decided to use a piece of bent ¼” tubing and attach it to the switch as shown below. I drilled a 1/8” hole and tapped it for a 3mm screw.

You need to do a little shaping of the switch as shown in the picture. 

The switch parts

I used rubber grommets to seat the metal lever. I thought they would keep the lever taut but still easy enough to move with a finger:
Zinc rod with grommets
When you’re done with these steps you should have a set of parts that look like this:
The parts ready for assembly
Once the parts have been made and test fit it’s time for welding. Weld the heater tube to the main tube first, then clean up the weld:

The first weld

After that weld the tube assembly onto the base plate:

Using magnets and a block of wood to position the weld

When you’re done it will look like this:

The completed piece, except for foam gasket
The next step is to find a foam or rubber gasket to use between the door and the switch. That will have to wait for the car to come back from the shop.

That’s all there is to it. I spent about 8 hours over a couple of days making this start to finish, but I got the satisfaction of making my own part. You can too!

If you have any questions feel free to drop me a line at

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