I assume that's the main motor in the air handler? The blower motor was replaced earlier this year, so presumably has some warranty - will check. I'm reasonably competent with basic electrical, replacing circuit boards, etc. If not the motor, is the fan relay a reasonably affordable part I can just replace and gamble on it fixing, skipping the diagnostic step or paying yet more money servicing this old thing?
As follow-up feedback, the answer turned out to be a poor connection on one of the thermostat wires under the house, resulting in a low voltage signal for heating. The tech had a helluva time finding it, but he did, and I was only charged their $89 diagnostics charge so was very happy to get off so cheap. Your feedback was helpful, though. Thanks.