With the black connectors on the top sensor and AC running I unplugged the sensor via the pigtail with the white connectors and jumpered the two white connectors from the pigtail together and no fan. I can't see it would make any difference to leave them connected to the switch as a short (jumper) would become the shortest path and the switch down stream in parallel would make no difference. Would this confirm the problem is either the relay or the resistor?