I have replaced our themostat three different times. This winter, but come to find out it is the switch that makes the fan turn on manual or auto there seems to be 4 wire connecting to it. You have to bump it sometimes to make it come on . It looks like a rocker switch to me what exactly is it called?

Fan limit control switch. They come in different lengths so you will need to know the element length to replace it. Any universal part can take its place.