Gas furnace made roger white 505a-241 contaroller flash 3 times error code that means pressure switch stuck open. I don't know and where is the pressur switch. Please help.



Thanks

Find the small blower that pulls combustion air through the heat exchanger. The pressure switch, or at least the hose leading to, it will be between the blower and the heat exchanger. It will have a couple of wires leading to the control board. They may have numbers on them you can check on the schematic.

Turn the main power off going to the furnace and then back on this will reset the control board. Turn thermostat back on and see if it works. If not take a screwdriver handel end tap lightly on the round pancake looking part above the burners. (two or three wires and a rubber hose will conect to this part). Good luck.

The tubing to the induced draft proving switch is attached to a barbed port on the inducer motor assembly, this port clogs requiring clearing.
Try this, call for heat and after the induced draft motor starts jumper the pressure switched leads together, the ignition should begin, if so your ignition and gas valve are OK it's the port or less often the switch is defective. But clear the port or you will replace the switch to no gain. A clogged furnace condensate drain can do this too.