Old Line Stat at Church

Old (1955?) Honeywell (actually M-H) stat T42A1X3 at church. Did an off-line checkout, painted bellows with hot/cold water and checked action and contacts. All OK. When I hooked it back up, it seemed to have a dead-band of about 3 degrees. Obviously, no anticipation, where did the deadband come from? This thing even has a little copper spring designed to prevent slop in the mercury switch. I looked at the action and saw no adj. for deadband, can I minimize this?
Tim S.
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This is Turtle.
Adjustment did not come into play till the Mid to Late 1950's. We as Americans got Picky and wanted less swing like 1 to 1.5 degree band. You need to modernize with a new one. I started in the business in 1956 as a helper in my fathers business and there was half adjustiable and half none adjustiable. The high dollar jobs got adjustiable and poor man jobs got none adjustiable because of cost. Adjustiable as almost $2.00 and none adjustiable was about $1.50. Now the total 4 ton cooling and 100K gas furnace installed was about $600.00.
TURTLE
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That's part of my point. This thing has a deadband, under load, with only the 2 contacts in the bulb. I know it's not, but it's almost like the mercury is magnetic to the contacts. Could there be enough (more) surface tension under load to hold the mercury to the contacts more than when just an ohmeter is the load?

checked
degrees.
the
this?
Americans got Picky and wanted less swing like 1 to 1.5 degree

1956 as a helper in my fathers business and there was half

adjustiable and poor man jobs got none adjustiable because of cost.

total 4 ton cooling and 100K gas furnace installed was

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This is Turtle.
The setting of the off and on band is determine by a electric heater built into the thermostat that will put out heat to the spring attached to the bulb and will turn the system off a hair before time to not have a over shoot of temperature. When you have a ohm meter on it . It will not have this false heat to turn it off a hair before time to not over shoot. So there is a false heat being put to the thermostat when under power and with the ohm meter this false heat will not become apart of the operation and the band differencial will be different. I can't remember the operation of the bellows type thermostat for it has been a few years since I worked on one.
TURTLE
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