American Stanard 90% Furnace

Bob C._2

Model AUY

3 fLASH CODE

COULD BE Venting problem

Inducer problem

pressure switch problem

circuit board has been replaced-Inducer has been replaced-vent and intake has been inspected- occasional 3 flash lockout-could it be preesure switch what is best way to test-1st stage switch 1.25" 2nd stage 2.25" suggestions thoughts how to troubleshoot thanks and god bless

John Mills_5

Remove the intake and vent

If the inducer isn't even trying or if it still doesn't run with vent & intake off, tell the HO to bend over. Bad inducer and only way to replace is buy an expensive kit which includes board, inducer and all new wiring harness. Have to replace the current inducer with new 3 phase model, new board and all the wiring. Allow several hours.



Now, you might get lucky and she fires. Then all you have to do is figure out what's blocked and what to do about it.



If you want to be scientific, see if vent is pulling enough vacuum instead of removing the pipes.

drhvac

pressure switch

Did you take a pressure reading with a manometer to see if it is higher or lower than the pressure switch cut in? This should be the first thing to do. Is the vent and combustin air pipe sized correctly?

furnacefigher15

Ditto

Like Drhvac said.



You need to use a manometer, or magnehelic gauge to test actual vacuum.



And I'll go a step further and say that you need to use a 2 port manometer. Connect to the system the same way the pressure switch does. You will need to use some pneumatic tees to make this happen. If the pressure is higher then switches ratings, then replace the switches.



If the motor runs, but does not make the pressure/vacuum needed, then look at the venting, and one other simple thing is the port on the inducer housing that feeds the pressure switches sometimes gets plugged with debris. A small allen key is an easy way to clean them out.