Nordyne furnace blower will not come on. Furnace heats up but fan never comes on... even when switched to "on" at thermostat. We've checked all wiring. We're thinking it must be the sequencer. How do we know which one runs the blower?

Post the model number.

When the fan switch on the thermostat is set to "ON", the relay that turns the fan on should be activated. If fan does not run when set to "ON' it is more likely to be a defective relay, fan capacitor if there is one, or the fan itself. The circuit would be through the sequencer only when in the "Heat" position.