That is the fan/limit switch. Jumper the red and blue wires and if the
blower comes on,the switch is your problem. The switches do not give a
whole lot of trouble, but they do fail, and replacement is easy. As I
said in the earlier thread, be sure and cut the little brass jumper at
the bottom of the switch, or you can/will fry most or all of the 24
volt components in the system. BTDT. Larry