Welcome to the forums! Do you happen to have the make and model number of the furnace? From what little memory I have left popups typically used gravity feed furnaces, some used blowers some didn't. The number plate should be under the front inside cover.
Aaron
__________________ There is madness to my methods
2015 Coleman CM16FBS(traded) 2016 Concord 300DS
2015 Ford Fusion Hybrid following along