You did not say if the heaters came on or not. Just that the fan no
start. A lot of times there is a sail switch in the duct work for
safety. If this switch does not move and close the heaters cannot come
on. Motor start is one thing but how about the heater elements. Also
there may be an overload switch near the heaters. If it gets to hot the
heaters will shut down. It is about the size of a half dollar. ( Banks
might still have a couple on hand if you need a reminder. ) As for the
capacitor try starting the furnace, then shut off the breaker or
disconnect. Then remove the wires from the capacitor , if there is a
resistor between the terminals cut the thing off. then short across the
terminals with a screwdriver,.make sure it is insulated drive not one
with an old broken wooden handle . If it snaps the cap is good . The
resistor was only there to bleed off the cap when power was off so don't
really have to worry about replacing. Run capacitors are oval with low
micro-fared ( 5=15 mfd at maybe 300volts). Start caps are round and
high like 80 or so. Also check the relay that pulls in the power to the
motor. Lot of mfg had a lot of different ways for safety. so follow the
wiring if you can. After you get your hands out of the furnace THEN go
turn the breaker on.