That is correct. What happens,
24 v leaves transformer
24v arrives at thermostat
thermostat decides what function
thermostat sends 24 v to air handle "cool"
air handler "cool"sends the 24v to outside
outside condenser receives 24 at the contactor
24v now leaves contactor to head "home" to common
24 arrives at C for common at the pcb
the pcb sends 24 v common on transformer.
So that is the journey the 24v took until it arrived at C. We want to interrupt the 24v just before it reaches C on the pcb and see if there is no short. If fuse is ok with C unhooked, we know we do not have a short to ground. If it blows fuse hooked to C, then pcb bad
Sorry to ramble so much but I try to simplify the circuit.