Carrier/Bryant units take some patients.
On Lennox units that don't have cased coils on top, most of the time I will remove the top cap of the furnace, remove burner door cover, and remove the top cap of the burner box and gain access from the top side with the flame sensor still installed.
Just be careful you don't bend it back and forth as your cleaning. I can even remove the flame sensor with the rubber tee in place using a magnetic stubby 1/4". Not too difficult, just use patients.