York PM9B12N060UP11A Tech support could not assist

[ainsworthCA]

Modulating gas furnace. having pressure switch issues, here is what I have found.

system is designed to start and fire at 75% capacity, once flame proves it will ramp down to 35% for 6 minutes. every minute after this the unit will ramp up continually.

upon start up, ive got 1.1 in w.c coming to my pressure switch from my inducer housing. switch is set to .60wc
once flame is proven, unit ramps down to 35%, at this time I read .50 in wc.

the inducer motor is a two wire, it is modulated thought voltage modulation from the board, the pressure switch is in parallel with an pressure transducer, this transducer creates a DC signal which in turn tells the board what to run the inducer motor at and gas valve. at 35%  I was reading 70v. there are no ports to test the DC signal the transducer is creating, thus they could not help but say replace the board as the transducer is soldered into the board.

new board has testing connections and a new gas valve because it will modulate the gas valve with my dc transducer signal.

my end result is replace the board/valve. but this is costly if I am mistaken

has anyone seen these issues before?

I don't think its the inducer because if I manually block airflow to transducer the motor will ramp up. as it ramps up the voltage goes from 70v - 120.

I don't think its a drain issue as this pressure switch is a dual for the burner box and inducer.
then I thought it could be a cracked heat exchanger and I will be testing with a combustion analayser in the morning as I didn't have it at the time. this building is unoccupied.

I'm flustered that no tech support technician can help me with this they all suggest replace the board. but at 1000 plus dollar my cost, if there is another issue I'm missing it wont be good.

suggestions to look for let me know. thanks

[Sergroum]

I've had calls where I kept getting pressure switch stuck closed due to a faulty transducer. At the same time, those transducers werent soldered into the board, they were separate and connected to pressure switches with a tubing. So I only needed to change the transducer alone. Kind of crappy to change the entire board, just for the transducer. But I can say that I have indeed had calls where the error shown was pressure switch stuck closed and the problem was with the transducer.