found this a couple months ago. customer called and said the unit is not keeping up. 2 stage furnace, ran great in low fire. high fire would set it off on pressure swtich. this is what i found. and this unit has been running like this for 3yrs. now boss said that can't be it. its been running for 3yrs. he is mad because i went out after him and we haven't heard back from the HO since i was there