Probably 1977 , is about right, from product numbers
C26-P0606
2-77-2P
Does whatever fills the tube change its character over the decades,
expanding for any given temp?. Leaking I could understand causing
problem, but that would be one-off.
Does not seem to be any wear on the pivotted rocking plate inside , that
transfers bellows motion to microswitch plunger. Other pivot point moves
via cam action of the dial up knob, unlikely that is worn.
Over time the setpoint on the dial has had to go up and up and now it is
effectively off the top of thse scale and microswitch is hardly on.
There is adjustment inside for the switching point of the microswitch,
which at half the stem is probably correct. If the rocking plate bent
wiht the pressures then I'd expect to see too low a set point developing.
I'll take some temp / bellows deflection data just out of interest, but
also confirm it has reasonable linearity.
The original setting of the pivot seems to be by choice of the
deformations in the pivot/rocker plate, no way of setting at initial
assembly other than go/no-go testing of each one.
"Sensor" tube is well buried and next to impossible to replace with new,
entire or partial because impossible to make a join in the capilliary.

N_Cook wrote:

Probably 1977 , is about right, from product numbers
C26-P0606
2-77-2P
Does whatever fills the tube change its character over the decades,
expanding for any given temp?. Leaking I could understand causing
problem, but that would be one-off.
Does not seem to be any wear on the pivotted rocking plate inside , that
transfers bellows motion to microswitch plunger. Other pivot point moves
via cam action of the dial up knob, unlikely that is worn.
Over time the setpoint on the dial has had to go up and up and now it is
effectively off the top of thse scale and microswitch is hardly on.
There is adjustment inside for the switching point of the microswitch,
which at half the stem is probably correct. If the rocking plate bent
wiht the pressures then I'd expect to see too low a set point developing.
I'll take some temp / bellows deflection data just out of interest, but
also confirm it has reasonable linearity.
The original setting of the pivot seems to be by choice of the
deformations in the pivot/rocker plate, no way of setting at initial
assembly other than go/no-go testing of each one.
"Sensor" tube is well buried and next to impossible to replace with new,
entire or partial because impossible to make a join in the capilliary.
It is a leak. Probably an insanely tiny one, if it is only showing up after
almost 40 years. The fill is usally a Freon appropriate for the temperature
range.

Jon

On 15/05/2016 17:31, Jon Elson wrote:
N_Cook wrote:

Probably 1977 , is about right, from product numbers
C26-P0606
2-77-2P
Does whatever fills the tube change its character over the decades,
expanding for any given temp?. Leaking I could understand causing
problem, but that would be one-off.
Does not seem to be any wear on the pivotted rocking plate inside , that
transfers bellows motion to microswitch plunger. Other pivot point moves
via cam action of the dial up knob, unlikely that is worn.
Over time the setpoint on the dial has had to go up and up and now it is
effectively off the top of thse scale and microswitch is hardly on.
There is adjustment inside for the switching point of the microswitch,
which at half the stem is probably correct. If the rocking plate bent
wiht the pressures then I'd expect to see too low a set point developing.
I'll take some temp / bellows deflection data just out of interest, but
also confirm it has reasonable linearity.
The original setting of the pivot seems to be by choice of the
deformations in the pivot/rocker plate, no way of setting at initial
assembly other than go/no-go testing of each one.
"Sensor" tube is well buried and next to impossible to replace with new,
entire or partial because impossible to make a join in the capilliary.
It is a leak. Probably an insanely tiny one, if it is only showing up after
almost 40 years. The fill is usally a Freon appropriate for the temperature
range.

Jon


Surely a leak would mean the pressure would not convey between sensor
end and diaphragm end. With this one the diaphragm must be too
extended/too much pressure, pushing the trip structure to the high end
of its range. A leak would mean the microswitch would not trip at any
set of the dial, low or high

Yeah, these things are generally replaced as a unit.

Here, we got a local WW Grainger where I would take it for a replacement, there, I don't know what to tell you. There has to be some kind of appliance parts vendors up there.

Nice thing is that the manufacturers of AC/refrig/whatever have a tendency to buy thermostats rather than manufacture them in house. Many of them are standard parts from Honeywell or Johnson or somebody, and they DO have overlapping product lines.

"With this one the diaphragm must be too
extended/too much pressure"

Hold on here. You have a knack for leaving out details. Somehow I assumed you are dealing with an AC or refrigerator not getting cold enough, short cycling. If that is the case your suppositions about the gas are wrong because things expand when heated.

Start from the beginning, what is this thing and what is it doing or not doing right ?

On 15/05/2016 17:31, Jon Elson wrote:
N_Cook wrote:

Probably 1977 , is about right, from product numbers
C26-P0606
2-77-2P
Does whatever fills the tube change its character over the decades,
expanding for any given temp?. Leaking I could understand causing
problem, but that would be one-off.
Does not seem to be any wear on the pivotted rocking plate inside , that
transfers bellows motion to microswitch plunger. Other pivot point moves
via cam action of the dial up knob, unlikely that is worn.
Over time the setpoint on the dial has had to go up and up and now it is
effectively off the top of thse scale and microswitch is hardly on.
There is adjustment inside for the switching point of the microswitch,
which at half the stem is probably correct. If the rocking plate bent
wiht the pressures then I'd expect to see too low a set point developing.
I'll take some temp / bellows deflection data just out of interest, but
also confirm it has reasonable linearity.
The original setting of the pivot seems to be by choice of the
deformations in the pivot/rocker plate, no way of setting at initial
assembly other than go/no-go testing of each one.
"Sensor" tube is well buried and next to impossible to replace with new,
entire or partial because impossible to make a join in the capilliary.
It is a leak. Probably an insanely tiny one, if it is only showing up after
almost 40 years. The fill is usally a Freon appropriate for the temperature
range.

Jon


Yes , long term leak. I'd got the action wrong. Idly thinking, I
remembered that with no function and turning off the power, the
microswittch made a click over noise. Normally off switch but only
because the spindle was pushed in , in the functionally off position and
released i nthe on position

In article , N_Cook
wrote:

Probably 1977 , is about right, from product numbers
C26-P0606
2-77-2P
Does whatever fills the tube change its character over the decades,
expanding for any given temp?. Leaking I could understand causing
problem, but that would be one-off.
Does not seem to be any wear on the pivotted rocking plate inside , that
transfers bellows motion to microswitch plunger. Other pivot point moves
via cam action of the dial up knob, unlikely that is worn.
Over time the setpoint on the dial has had to go up and up and now it is
effectively off the top of thse scale and microswitch is hardly on.
There is adjustment inside for the switching point of the microswitch,
which at half the stem is probably correct. If the rocking plate bent
wiht the pressures then I'd expect to see too low a set point developing.
I'll take some temp / bellows deflection data just out of interest, but
also confirm it has reasonable linearity.
The original setting of the pivot seems to be by choice of the
deformations in the pivot/rocker plate, no way of setting at initial
assembly other than go/no-go testing of each one.
"Sensor" tube is well buried and next to impossible to replace with new,
entire or partial because impossible to make a join in the capilliary.

Replace the microswitch. They wear over time.

Isaac

In article ,
Jon Elson wrote:

N_Cook wrote:

Probably 1977 , is about right, from product numbers
C26-P0606
2-77-2P
Does whatever fills the tube change its character over the decades,
expanding for any given temp?. Leaking I could understand causing
problem, but that would be one-off.
Does not seem to be any wear on the pivotted rocking plate inside , that
transfers bellows motion to microswitch plunger. Other pivot point moves
via cam action of the dial up knob, unlikely that is worn.
Over time the setpoint on the dial has had to go up and up and now it is
effectively off the top of thse scale and microswitch is hardly on.
There is adjustment inside for the switching point of the microswitch,
which at half the stem is probably correct. If the rocking plate bent
wiht the pressures then I'd expect to see too low a set point developing.
I'll take some temp / bellows deflection data just out of interest, but
also confirm it has reasonable linearity.
The original setting of the pivot seems to be by choice of the
deformations in the pivot/rocker plate, no way of setting at initial
assembly other than go/no-go testing of each one.
"Sensor" tube is well buried and next to impossible to replace with new,
entire or partial because impossible to make a join in the capilliary.
It is a leak. Probably an insanely tiny one, if it is only showing up after
almost 40 years. The fill is usally a Freon appropriate for the temperature
range.

Almost undoubtedly alcohol. If it were freon, it would all boil away no
matter how small the leak, because it would be pressurized.

Alcohol, because it's non-corrosive (while water is). All it needs to do
is convey the volume change from the bulb without friction, to make the
bellows expand.

Isaac