My furnace will start and works tntil the blower motor should start. Then it goes and shuts off and flashes a code 33. I have replaced the motor capacitor. The motor is fine. I do a 3hr resety and it does the same thing. The blower comes on, the gas comnes on for 90 seconds and then it shuts down.

Will the blower run after the burners start up? If not you may have a bad control board. If the blower runs after the burners start then locks out on high limit check for air flow restriction. Turn your thermostat fan switch to on with the blower running all the time turn your heat on. If it keeps heating you got a bad board.