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If circuit breaker is tripping we either have a motor drawing high amps or a dead short.
The 3 flashes indicates pressure switch is not closing.On call for heat does the small vent fan come on?
OK, that makes a difference. Now your furnace has 2 motors. A small inducer (vent motor) and the main circulating blower motor, On call for heat the small inducer motor must come on and suck a vacuum on the pressure switch which is attached by a small rubber hose. Our fist step is to verify if that small motor is coming on.
Inducer will be where vent connects and look similar to this