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my name is Billy.
The 24v starts in the air handler from the 24v transformer....goes to thermostat and waits to see what wire the thermostat is going to send it back on.
In heat it gets sent back on the W wire and goes to a sequencer. This sequencer is a stacked switch that turns on each level one at a time.
First is blower...then is stage heat and then if equipped 2nd stage heat.
If you get blower but no heat you likely have a bad sequencer.