Capilliary tube thermostat problem

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.
Reply to
N_Cook
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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

Reply to
Jon Elson

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

Reply to
N_Cook

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.

Reply to
jurb6006

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 ?

Reply to
jurb6006

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

Reply to
N_Cook

Replace the microswitch. They wear over time.

Isaac

Reply to
isw

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

Reply to
isw

On Sun, 15 May 2016 16:16:27 +0100, N_Cook wrote as underneath :

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+

Reply to
Charlie+

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