I purchased a property with the Sears Kenmore 600 Series Model 867.733531 wall mounted natural gas heating unit that isn't working right. The burner starts when I switch it to automatic, but the fan won't start and the heat doesn't shut off on high heat. The fan only comes on in manual mode. I believe the problem is in the Thermo Discs, It has three Thermo Discs, 2 are the two wire type, the third is a three wire type. I would like to get a wiring diagram or at least a clue as to the operating functions of the three discs and the rotary control switch. I'm thinking I may have two bad switches, one to start the fan and the other to turn off the burner on high heat.

Thanks

I also have an old series 600 heater from sears. I found a book either on the Kenmore or sears site for a 600 model number 867.736349 and 867.736389 and although my model was 867.73361, the wiring was practically identical. My furnace has three thermal switches mounted about half way up from the floor. The one on the left is a limit control and should always have voltage passing through it while power is supplied to the unit, unless it detects an overheat condition. Then it will open killing voltage to the transformer that activates the gas valve. The thermal switch in the middle should close and supply voltage to the blower after the furnace gets the inside of the cabinet to between 140 and 180 degrees. The thermal switch on the right is a fan speed switch, which will increase the speed of the fan if temperatures inside the cabinet reach a set level. Be careful when measuring these voltages, they are 120 volts AC. Good luck.