furnace runs for a bit then no fire
hey I have a Lennox furnace, that the inducer motor will come on and spin for like 2 or 3 seconds and then shuts off. it will come back on after a few minutes and do the same thing again.I check the pressure, it is kicking in the pressure switch. on the schematic it shows a limit switch after the pressure sensor, if I take the wire off of that pressure sensor the indoor blower motor starts to turn instantly. in about 1 minute the inducer motor will spend and the furnace fires like normalit will run for about 10 or 15 minutes and then shut down. when it starts up it may or may not fire, if it does the burners will come on for about 1 minute and just before the blow motor comes on the burners go out. if I pull that wire off of that limit switch again it starts all over but never runs more than 15 minutes or so. I am NOT leaving that wire off I just momentarily take it off and put it back on when the blower motor starts.
the lights on the unit blink normal green no matter what happens
any clues what to test next or where to start?