Furnace Help. Stumped

[Plumber69]

American Standard furnace freedom 90. 1 stage.
Furnace is intermittent. Code 3 pressure issue.
Tested with manometer getting 1.5wc, switch is rated 1.15wc

Ive narrowed it down to this

If I take the black tube off top of pressure switch that goes to gas valve and burner box everything works

if I open burner chamber everything works.

If I remove fresh air pipe everything works
I vacuumed and snaked the fresh air pipe.
Furnace is 10 years old.
Am I supposed to have equalized pressure in the burner box?

 

[Plumber69]

Burner box seems to be sucking air in thru tube connected to top of air switch making it harder to close.

 

[Sponsor]

 

[Fitter30]

Model number ?

 

[DavidDeBord]

Wow! It's highly unusual for an HO to have & know how to use a Manometer -- I'm Impressed.

What does the Manual/ Data sticker say that a Code 3 is?

"If I take the black tube off top of pressure switch that goes to gas valve and burner box everything works"

With the 24V wires still connected? It should not have worked

From what You've stated,.... You either have a Stuck/Failed Pressure switch, or some form of restriction within it/ or the tubing. Blow out the tubing & se if a "Goofer feather" or something comes out.

Jumper across the the 24 V. terminals on the switch, & see if everything works, when you have it all put together, if so, then it's definitely the switch, but,..... Also check the induced draft fan, is it running hot? plugged with dirt? Running slow? If You have a Amp meter, take a reading, & check to see what the Amp draw is per the Induced fan data plate. a slow running fan, will also cause the contacts in the Pressure switch to not close.

And, since this is a Condensing Gas Furnace,... What color is the Condensate? It should be Clear, & not coffee colored,.. If it is, You may have caught a major problem, before it gets outa hand.

 

[Plumber69]

pressure switch was changed. continuity flicks on off sometimes with vent on. mostly off. Condensate is clear. with the tube from the pressure switch to gas valve and burner box be neutral?

 

[Plumber69]

pressure switch was changed. continuity flicks on off sometimes with vent on. mostly off. Condensate is clear. with the tube from the pressure switch to gas valve and burner box be neutral?

Ive tested all that. Should it be neutral air pressure in burner box

 

[Plumber69]

someone told me weak inducer. Wouldn't that pull more air

 

[DavidDeBord]

someone told me weak inducer. Wouldn't that pull more air

Plumber, can you provide the Md.# & Ser.#s?

A Weak inducer fan, will not pull/push more air,... It will move less air.

And, check Your Combustion air pipe for restrictions.

"continuity flicks on off sometimes with vent on" <<< I'm not sure what you mean by that.