Unit: "Old" Sears Furnace Age: Unknown; Model#: 867.763271; A/C: Kenmore condenser/cooling coil are newer add-ons probably mid-90's; Blower Fan: Emerson 1/3 hp direct drive, looks-like updated model.

Problem: Recently, the blower fan on our furnace stopped running and yet the condenser continued to run. While inspecting the blower fan, I found a manual circulation switch on the bottom of the Electrical Comfort Center inside the furnace and switched it on and the blower fan started. I suspect the double pole double throw Plug-In Relay, but not sure how-to test it to verify. Any other suggestions would be greatly appreciated. Thanks.

With tstat calling for fan on with meter check for power coming out of relay going to motor,make sure you no there is power going into relay and coming out

Also check for the 24 volts at relay coil.
With 24 volts present and 240 volt power at input of relay, you should get power out of relay(240 volts)