[T3] my long term issue have to unplug TS1 for a smooth idle.

[Jim Adney]

On 1 Oct 2019 at 11:03, William Jahn wrote:

> You can't get the flat wound thermal spring on wrong because the
> valve stem is slotted to fit the inner most part of the spring the a hole
> in the slotted shaft for the screw and spring for the +/- adjustment the
> hole is slotted .

I'm at a disadvantage here because I've never been inside one of the AT 
AARs, but I'm willing to believe that the design is at least similar to the MT 
version. The MT version was designed first and the only change they had to 
make was to add electric heat to the the AT version. The parts you describe 
sound much the same as the MT version.

With the slotted shaft, it's easy to rotate the spring by 180 deg.

When adjusting the +/- screw in the slot. It's easy to over/under-think that 
and get it backwards.

> Over years of heating and cooling cycles I imagine the spring changes I
> just adjusted to the far end of the slot so it would close sooner it's
> marked with a red dot center on screw factory calibration. 

The MT versions don't seem to have a problem with the "spring." The only 
problem they have is that the zinc metal housing warps over time and 
causes the valve to stick. I regularly fix these. The AT version also appears 
to have a zinc die cast housing, but it's much harder to take apart. That's 
unfortunate, because the only problem I've seen with them is that they get 
stuck in one position.

That "spring" is a bimetal strip, a very well understood mechanical temp 
sensor. I don't see long term fatigue problems in these at all. All older 
heating thermostats have them, and they last for decades. I replaced our 
home thermostat a few years ago, but not because of the bimetal strip. That 
thermostat was nearly 80 years old by that time. I know someone at 
Honeywell who once told me that the only thing that ever fails in their old 
round thermostats was the wires that flex every time the bimetal spring 
moves the mecury capsule. They don't sell thermostats with mercury any 
more, but the old ones never had trouble with the bimetal strips (which were 
also wound in a spiral, like our AARs.)  

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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