1950s 1956 A/C thermostat repair

[Cadman-iac]

I have been working on repairing two A/C thermostats I've got for my 56 Coupe Deville.
The nichrome wire heating elements have gone bad, so I'm trying to replace them.

I had a small piece of the  .006" nichrome wire, and I got some fiberglass wire covering from Jose Gomez with a 1MM diameter, apparently the smallest available.
After I finally got the wire threaded through the covering, I began to wrap it around the capillary tube from the tip up to the t-stat bellows. Unfortunately about halfway through I felt the wire break inside the covering.
So at this point, I'm now out of the .006" wire, but I did have some  .012" wire. So  I thought I'd try it again with the bigger size wire. It gets hotter faster, but I'm hoping it won't make too much of a difference. The thermostat can be adjusted to compensate for the additional heat. (I think, I hope).
  So after getting the .012" wires wound around the capillary tube and wrapped around the base of the bellows,  I used Plaster of Paris to insulate the wire just like what the factory used.

These pictures show what I'm talking about. The first picture is one that Jose Gomez had posted on another thread showing the diameter and the lengths for each wire which he highlighted, along with the schematic for the A/C control circuits. I am posting this for reference purposes.
  The second picture is one of the thermostats after I wound the insulated wire around the capillary tube and the base of the bellows.

The third picture is of a thermostat with the original wire still on it, next to the one I just did with the bigger wire. You can see the difference in the amount of tube that the new insulation is covering versus the original one.

  Anyway, I am wondering if anyone has any experience with these thermostats and how they are supposed to operate. Will the thermostat work using heavier heating wires and compensating for the additional heat by adjusting the temperature setting?

Monday I ordered a roll of the correct size wire, and more of the covering for it, so I can make it like original.

One thing that I have noticed is that the new wire covering is wider than the original wire cover/insulation was. Once both new wires are in place, they cover almost half of the surface area of the capillary tube.
I believe that that will have an effect on what the capillary tube senses too, (less exposed tube, more heating wire insulation).

  Also, I'm not sure about this, but I think that the shorter the wire, the hotter it will get, given that the voltage is the same for both wires, is this correct?

  It's Wednesday and I just got the new nichrome wire in, I had to buy a 1/8lb roll, which is 1120ft.
I can break a few wires now!

The next thing I need to do is figure out how to connect the nichrome wire to the terminals on the thermostat. The factory had cut very slight grooves in the rivets that keep the terminals in place, and they pinched the wire into those grooves. Unfortunately I can't open up the original grooves in order to install the new wires, and I have no way of cutting my own grooves in the rivets.  So I'm guessing that maybe I can solder them on, and hope that the current flow is not high enough to melt the solder when the circuit is called for.
I don't think I can weld the wires to the rivets, although someone had told me that is what they did. All I have is an old arc welder and a big Miller 200 mig welder, neither of which will adjust down far enough for the precision welding needed here.
So I'm open to suggestions if anyone has any ideas about how to connect a .006" nichrome wire to a brass rivet that's embedded in a very small piece of plastic.
Now that I've spelled it all out and thought about it, I'm not sure that soldering it would be a good idea either, because of the plastic parts involved and the heat it would take to solder them together.
I've considered drilling out the rivets and replacing them with new ones, but again, the parts are very delicate and irreplaceable.

I'm sorry if I'm rambling on here, I'm just thinking out loud and trying to figure out what to do next, and looking for advice from anyone that might have some experience with this sort of thing.

  So today, Thursday, I replaced the wire and insulation on the second thermostat using the new correct .006" nichrome wire.  I had to pull the larger wire out of the insulation and reuse the insulation. The stuff I ordered was supposed to be 1/16" in diameter, but what I got looks more like a jump rope, so back to the drawing board for that. (Oops)!

  The fourth and fifth pictures are of one of the tops of the thermostats that I've taken loose in order to test the capillary tube. As you can see, there's not much to connect to. The heating wires are supposed to be crimped to the end of the brass rivets that holds terminal numbers 1 and 4. And these are not just a pop rivet, they appear to be pressed once they are inserted through the terminal and the internal connector.
Such a complicated piece for the times.

  Here's a picture of the second thermostat after installing the new wires and the Plaster of Paris to insulate it with. Looks pretty good to me actually.
So once I'm ready to get the A/C  going, I figure that I'll start with the thermostat with the correct size wire and see how it works, and hopefully, there won't be any problems, but if there are, I'll switch to the other thermostat with the bigger size wire, and see if that works better.
Of course, the testing of this stuff will be a ways off in the future.  Gotta get the car back together before I can test the A/C system.
One thing at a time, one thing at a time, unfortunately, I can only do one thing at a time. Old age sucks!!

Anyway, if anyone has any questions or suggestions on any of the things I've mentioned, please, feel free to ask questions or give me your thoughts, advice. All is appreciated.

  Rick

[Cadman-iac]

These are both rewired now. The one on the left has the .006" wire, but I still have to solder the wires at the end of the tube, the right one has the .012" heavier wire and the Plaster of Paris applied.

 Rick

[Cadman-iac]

This shows how much difference there is between the original wire and insulation, (bottom one), and the new wire and insulation, (top), and I've only gotten one of the new wires on here when I took the picture.

  Rick

[Cadman-iac]

4th and 5th pics. Thermostat top where the connections are.

  Rick

[Cadman-iac]

After the Plaster of Paris is applied to the second thermostat.

 Rick

[Cadman-iac]

 The bracket that the thermostat is mounted to in order to mount it on the evaporator case, has a small approximately 1/2" hole in it that the capillary tube goes through. It is very difficult to remove the thermostat from the bracket without damaging the heating wires. You have to rotate it in order to basically thread the capillary tube through the bracket.
 Once the new wires are in place, since they are a bit bigger now due to the insulation, trying to thread the tube back through the hole is impossible without damage.
 To fix this problem, I've drilled the hole out to around 7/8", so the tube will fit much easier. To take up the difference in the size of the hole, I'll use a small rubber grommet.
 The factory didn't have anything to block off the hole to prevent air from escaping, but because I've enlarged the hole, I think it's probably a good idea to reduce the air leak that a larger hole creates. (It probably wouldn't make any difference, but why not try to prevent an issue, right?).

 So in this first picture are 2 of the brackets, an original, and the one I drilled.

 The next few pictures show the thermostat mounted to the bracket and you can see how the tube fits through it. Not much room even after drilling it out.

 Rick

[Cadman-iac]

  So after thinking about how to connect the nichrome wire to the terminals on the thermostat, I've had a couple of ideas.
The first idea was to drill out and replace the rivets that hold the terminals in place, however, that has a few drawbacks. First, just the process of drilling the original rivets out is risky, as damage to the main piece is highly likely since it's plastic. Any bit off center and the plastic will be the sacrificial piece, which is not an option. Secondly, finding an acceptable replacement rivet is nearly impossible. If I did happen to locate some, most places would want to sell you a box of 100 or 1000.
  Pop rivets wouldn't work because they would put too much pressure on the plastic parts, and just getting the tool into position would not be easy due to its size, and the wire would have to be inserted under the head of the rivet, and if there were any problems, then you would have to drill the rivet again, risking damage yet again.
Even if I found the exact same thing that the factory used, those were pressed to lock them in place, which I wouldn't be able to do. And the factory had crimped the wire into the head of the rivet, making it permanent, which if things lasted forever, wouldn't be a problem. But I'm looking at this with the idea that if the wire went bad, then I'd like to be able to repair it again, I'd have to repair it again, as you can't get another one.

So another idea occurred to me today, drill a very small hole through the center of each rivet, on the order of .020" to .030" diameter.  Just enough that the wires could be inserted into the hole and soldered. Being soldered, it would be possible to unsolder it if necessary without damaging the plastic parts.
Since the rivets appear to be made of brass, they should be able to be drilled fairly easily, provided I can find a decent drill bit in the right size.
I'll update as things progress.

  Rick

  Edit: I enlarged the picture of the rivets on the thermostat control so you could see how the factory had attached the wires to them. If you enlarge the picture yourself, you can clearly see the remains of the original wire sticking out from the ends of each rivet, and you can see where they had pinched the groove in the end of each rivet to lock the wire in.

[Cadman-iac]

  YESSSSS!!!!!
 
 Well, I decided to go for it and try drilling through each of the brass rivets today. I happened to have in stock 4 small jeweler drill bits,  .0465" in diameter. It's a good thing I had 4, because it took all 4 to do this. They were pretty delicate, but they cut through the brass like butter.

  So here's what they look like now. I put a short piece of copper wire through each rivet to show that the holes go all the way through.

   Now when I put the thermostat back together, I can insert the nichrome wire into those rivets and solder them in. And if it's ever necessary to replace one or both of the wires, the ends at the rivets can be unsoldered and new wires soldered in, saving the thermostat from damage.
  I'm so happy that I've figured out how to connect the Nichrome wire without damage to the thermostat.
 But now I've got to get some more of those miniature drill bits. I've had these for over 10 years and never needed them until now.

  Rick
 

[Roger Zimmermann]

Richard, for me those drill bits (about 1.2mm) are rather large! I have difficulties to understand why you broke all four...

[The Tassie Devil(le)]

Sounds like he was too heavy-handed and overpowered the drills on breaking through at the end of the hole.

Bruce.

[Cadman-iac]

Richard, for me those drill bits (about 1.2mm) are rather large! I have difficulties to understand why you broke all four...

 Hi Roger,

 It was actually fairly easy. I was using a 3/8" power drill for the job, as the only drill press I have is an old Buffalo brand unit from the 40's
that stands almost 6 feet tall, and runs on 240 volts. Just a bit of overkill!
 I think what happened was the bits were catching as they broke through the other side, and as small as they were, it didn't take much to snap them.
 Ideally, I would have liked to use a miniature press, but you know that old saying, "wish in one hand and $h** in the other, and see which one fills up first".
 At least I had enough bits to get the job done.

 Rick

[Cadman-iac]

Sounds like he was too heavy-handed and overpowered the drills on breaking through at the end of the hole.

Bruce.

That's exactly what happened Bruce. I'm not used to using such a small size bit and just proceeded as usual. But after breaking the 2nd one, I was trying to be careful, but it's that last little bit that killed them.

 Rick

[Cadman-iac]

  Ok, I got these thermostats all put back together, with the new Nichrome wire of the correct size on both now. I decided to replace the wire on the one I had used a heavier wire on. I had to chip off the Plaster of Paris to get the wires unwrapped, then reapply it once I got the new wires in place.
 They both look great and best of all, they test out perfectly. So hopefully when I get to the point where I can install the air conditioning, everything will work fine.
 I do expect that I'll have to adjust them of course, but that's a given.
 Here's some pictures of how they turned out. The best thing about this is that if it's ever necessary, I can easily replace the Nichrome wire without damaging the terminals.
 I've still got to install a grommet on the second one. I also made new end covers for them as the old ones were in bad shape.

 Rick