Capilliary tube thermostat problem

[N_Cook]

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.

 

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 ?

 

[Jon Elson]

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

 

[N_Cook]

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

 

[N_Cook]

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

 

[isw]

In article <nha3ln$e0$1@dont-email.me>, N_Cook <diverse@tcp.co.uk>
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

 

[isw]

In article <R9adnR1Q3ubMOaXKnZ2dnUU7-VednZ2d@giganews.com>,
Jon Elson <elson@pico-systems.com> 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

 

[Charlie+]

On Sun, 15 May 2016 16:16:27 +0100, N_Cook <diverse@tcp.co.uk> wrote as
underneath :

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.

I checked out one of these units a few months ago, the mode of failure
was:
Microswitch contact plate (a beryllium spring click plate) was slightly
discoloured, this points to the contact resistance gone higher, leading
to heating of the sprung plate which then changed its clickover point
and characteristics. Like yours, the bellows unit, lever point tipover
contacts, preset springs etc were all fine and almost unworn. Had to
replace the unit, it could not be braught back into its (estimated)
spec. There is amost no real info on these units and trying to reset
them very difficult, at least I had a good try and failed to do it! C+