Hello I am working on a comfortmaker furnace it is a 80% and I am getting 3 blinking lights indicating the pressure switch will not close the inducer moter vent is clear and so is the exhaust vent I have replaced the pressure switch and it does the same thing. When I bypassed the pressure swtch to c if it would come on it did any suggestions on what the problem may be?

The pressure switch has a very flexible hose connected to it that goes to the draft inducer housing. Remove the hose carefully, as it splits easily, from the inducer housing and see if that fitting is clogged. When the inducer runs there is a small amount of air pressure that comes out of that fitting to send pressure to the pressure sensing switch.