the blower running for two minutes then shutting off sounds like the sail switch is not working
it has to sense airflow inorder to start the firing sequence.
1. airflow through the vents
2. voltage to the sparker
3. gas on
4 burner tries to fire, if n fire the sequence will shut try up to three times of sparking to get a flame/light off, if not it goes into lock out
5. internal thermostat monitor chamber temps on plenum, which regulates the burner on times and off times during the heating event
6. hot air out the vents.
finding schematics is getting crazy, i geuss because somebody blew themselves up
a quick rundown might be
adequate gas supply
good 12 volt supply to the furnace ( i would pull the fuse on it for a few minutes to let the brain reset)
no obstructins in the exhaust outlet or fresh air intake, wasp nest, spider webs, etc
when you turn it to heat and adjust the thermostat to come on, and the fan comes on, wait about 3-5 seconds and listen for the sparking or igniter noises, if you dont hear them then i would say the sail switch is not detecting adequate air flow or a fault has set in the ignition cycle,
but by all means please be careful around the gas supply and the ignitor and the power wires. no smking etc.... shut off power
Living in the Piney Woods of Texas.