Old ICP furnace, pressure switch code

ICP gas furnace GUA080A012EIN Light flashes 3 time: pressure switch stuck open. DMM reads that the switch is closed. DMM shows 24v going into the pressure switch to the blower and into and out of the high temp switch. Furnace will not heat with the pressure switch disconnected or with the wires shorted. Pressure switch is operational, but not tested with hydrostatic pressure meter. Im thinking its the White Rodgers control module. Ive exhausted all of my handiman ideas for trouble shooting. Any suggestions?