Electrical switch for primary control system for furnaces

Claim 1

In an electrical switch for use in a primary control system for furnaces, the combination including a housing having an end wall, a U-shaped mounting base having a web portion and a pair of spaced flange portions disposed in said housing, first and second bimetallic blades, one end portion of said first blade being fixed to one of said flange portions, the other end portion of said first blade being fixed directly to one end portion of said second blade, said first and second blades bending in opposite directions upon an increase in temperature, stop means carried by the other end portion of said second blade, a pair of resilient contact members fixed to said web portion of said base, said contact members being in electrical contact with each other when one of said members is in engagement with said stop means, adjusting screw means threadably engaging said one flange portion and bearing against said first bimetallic blade, said adjusting screw means being effective to adjust the position of said stop means carried by the other end portion of said second blade relative to said one contact member, electrical heating means encompassing said first blade and being effective to heat said first blade to cause said stop means to be disengaged from said one contact member responsive to bending of said first blade, the directions of bending of said first and second blades responsive to a change in temperature being such that an increase in temperature of said second blade will tend to counteract deflection of said stop means responsive to an equivalent increase in temperature of said first blade, a manually operable plunger, said plunger being supported for axial movement by the other of said flange portions and said end wall of said housing, said plunger sequentially engaging said contact members upon the application of manual force thereto and maintaining separation of said members until said one contact member engages said stop means, and resilient spring means bearing against said other flange portion and said plunger and biasing said plunger away from said one contact member and toward said end wall.