i have a goodman gmp 075-3 gas furnace. i woke up this morning and it was 59 in here.not freezing but certainly cold enough for me. i went to the furnace and i am getting three blinks. it says pressure switch failed to close.im a carpenter by trade so im pretty handy but i have no idea what a pressure switch is or where it is located. can anybody help. i just bought this house a year and a half ago,the furnace is about two or three years old id guess. in the yerar and a half ive been here ive had to replace the flame sensor twice. now this.is this common for goodman because im not going through this two or three times a year. i will gladly share some of my knowledgeof carpentry for anyone interested, but right now can some one help?please?