I just installed a NOMA 7-day programmable thermostat for an electric furnace/AC system (ceiling unit). I believe the wiring (5-wire) is correct.

When I set it to COOL with Fan set to AUTO, it turns on the A/C and the fan automatically. Good.

But when I set it to HEAT with Fan set to AUTO, it turns on the heating system but the fan doesn't. The fan does turn on when I force it by setting the switch to ON.

Any idea why?