Here you first question about thermostat... ,basically two wire which are short going to thermostat... you can check it from Multimetre... when your motor getting too hot... immediately themostat wire open the circuit ..means the same two wire( Green ,white) i think so... will be opened,black...
Diode
i think diode is 1n4004 and alway remember four diode is used for full wave rectification ..the four diode is used for rectification in any circuit only if output of transformer is connected to any of two diode.