trane 80% 2-stage

[newhvac]

I have a older 2-stage trane furnace 80%. First time checking the furnace the light on the board was flashing 3 times indicating pressure switch problem. I have no power going to inducer, diagnosis bad control board. after installing new board furnace fired correctly for 20-30 seconds and locked out again with pressure swicth problem. Both swicthes are open on iniatal call for heat. I never had this situation happen before just wondering if there is sommething i am missing. thanks alan.

[heatseeker]

buy a new board then when that doesn't work try another than another.

[derrold_d]

dont buy new boards first check and see if the pressure switch is opening by use of volt meter. most likely it is. next step why. most likely has a bad heat exchanger or plugged/poor flues. but you should have checkedthe flues already.

[how]

This problem is long gone but a pressure switch problem will not cause a power loss to the inducer. Possible thermostat circuit problem, board relay or inducer line connection is the only reason for no ID power while the furnace has power and a call for heat..
There are lots of different causes for why a pressure switch is not opening but the lack of voltage to the ID (if measured correctly) is a seperate issue.

[heatseeker]

how -
> This problem is long gone but a pressure switch problem will not cause a
> power loss to the inducer. Possible thermostat circuit problem, board relay
> or inducer line connection is the only reason for no ID power while the
> furnace has power and a call for heat..
> There are lots of different causes for why a pressure switch is not opening
> but the lack of voltage to the ID (if measured correctly) is a seperate
> issue.
It could have been a misbehaving switch.