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thumbkins 03-04-2011 04:34 PM

pressure switch
I've got an Armstrong downflow furnace that's about 4 yrs. old. Almost every other time it starts it shuts down with a code of pressure switch open. It doesn't happen all the time but when it does it annoys me and I know that something is not right. I've changed the pressure switch and it worked great for about two days then went back to doing it again. I took the tube off that goes from the inducer fan chamber to the pressure switch and blew thru it and nothing came out ( I was expecting maybe some condensation or a drop of water) When it does start and run it runs till the stat is satisfied then shuts off. When it does it's shut down thing, I hear the inducer motor start, the click for the ignitor, the flame starts, then the flame shuts down and the blower starts and runs for about 30 seconds.

I installed the furnace and installed all new "b" vent thru the roof replacing what was there. The furnace is the only thing tied to the flue. The furnace is an 80% unit. It was supposed to be a temp till I finished my remodeling, and I haven't finished yet.

I really hate this furnace it's noisey, there is rattling going on inside it and every year I have to replace the flame sensor or it creates another batch of problems. What can I say, it was cheap!!!!!

Any ideas would be greatly appreciated.


how 03-04-2011 05:12 PM

First common sense checks are...
Since you've replaced the pressure switch twice, make sure that the tube is not cracked anywhere and your tube conections to the switch are good, make sure you have good continuous electrical connections to the switch and anything else that is on that circuit, make sure you don't have sand like debris going into the pressure switch (only takes one grain to mess with it) make sure you have not connected your furnace vent to a larger size of B vent that is called for, bang on the underside of the horizontal section of your venting to the B vent to make sure there isn't a dead starling in there, do you notice any difference in the main burner flame after the blower comes on, does the sound of the inducer motor wind down a bit after the initial firing. After this point you are probably looking at a replacement inducer motor/turbine assy (a manometer would help here) or a motherboard change.
After eliminating the basics, we all start quessing.

thumbkins 03-04-2011 05:46 PM

Thanks for the response. I will check the items you listed. The mother board was changed when the furnace was in it's first heating season.
What kind of reading should I get with a manometer. It's in inches,right? How much?
There is no horizontal section of vent, it goes straight up and out.


how 03-04-2011 06:17 PM

If your manual doesn't say then get it's parts number from your owners manual and google it. You can also look at the info on the pressure switch for what is called for for that unit.

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