Pressure Switch Error

[rwaterson]

I have a Trane XR90 propane furnace that is not working for me. I get 3 flashing lights, which specifies that I am getting a Pressure Switch failure. I have done some troubleshooting and the situation is not getting any clearer. If I check continuity on the two connectors on the pressure switch when the inducer fan starts it DOES trigger, so it is sending the "good to go" signal to the control board. But the furnace never tries to light and I get the three flashes. I also checked voltage on the yellow wire going to the pressure switch and I am seeing 27-ish volts, so the board is sending power to it. I am leaning towards the idea that the control board is bad but I would hate to spend that money if that is not the case.

I would really appreciate any insights or help on this issue. Thanks!

[Hiroshi]

Remove the pressure tube and be sure it is clear. Then, remove the terminals from the control board one-by-one and replace them to interrupt any corrosion that may be forming... I would also test for the voltage at inducer start up to be sure the switch is passing the same volts it is receiving.

There is likely a "roll-out" hi limit switch you should check too... the pressure system is basically there to ensure there is positive air-flow before the unit kicks the burners on, think air-flow and inspect everything + change the filter if you haven't already.

Removing the control board and inspecting the solder side for burnt solder joints is also wise.

Provide us with the complete model number and one of the HVAC experts around here will be better able to guide your repair!

Edited December 12, 2016 by Hiroshi