ReplyIs it stuck open?
Is the venter motor working?
Regular Guest
Im having trouble figuring out why this 6 year old furnace wont close the pressure switch?
Professional Member*
Is it stuck open?
Is the venter motor working?
Regular Guest
the venter motor is working and I have replaced the pressure switch
Regular Guest
It seems to have to much negative pressure acording to out digital magnehelic guage. we taken off both the flue and freshair intalke and no change
Regular Guest
Ive replaced the pressure switch and cannot get the furnace to close the pressure switch. any ideas? ive removed the flue and fresh air intake and it did not change any thing.
Professional Member
Check the vacuum to the switch, maybe the line is plugged up or there is water in furnace due to a plugged drain.
Regular Guest
Checked all of that and thats not it. this is a very unusual situation and hard to figure out. Not a typical trouble call!Originally Posted by joeblo
Professional Member*
Believe it or not, the furnace drain can cause this! The corrugated hoses have to be switched based on left or right flow. They are tagged different colors with description on the panel.
Professional Member
Those corrugated hoses also can crack, and it can be difficult to spot. Be sure to check them.
Question authority!
Professional Member
pressure swith could be DOA
Professional Member*
What's your pressure compared to the switch? Is it a differential ps?
Regular Guest
The first thing is how much vacuum the furnace pulls with the intake and exhaust off. The drain could cause this problem. The secondary could be plugged, but this normally trips the roll out. make sure the black intake box under the burners is not plugged with a bird nest etc.
Professional Member
My bet is that there's a gallon of water in the secondary. Good old Carrier drain traps. I have days where I un-clog 3-4 of those in a row.
Pull the flex hose off the top of the drain trap.
Professional Member
The drain traps clog because the plastic lining in the secondary hx comes off, I call that a failed heat exchanger but carrier usually won't warranty it unless there are actually holes or completely plugged.
Regular Guest
Okay thanks to every one who responded to my problem. So everyone take note because it took some one who has worked installing and repairing carrier systems for several years to figure it out. He almost gave up on it but remembered once that whem installing a new 90% Carrier that there is a baffle in the fresh air intake black plastic that is installed from the factory and must be removed if the pvc fresh air run is longer than normal lengths. Once we removed the baffle the unit worked fine. This is something that is important to remember if you ever run into this problem. thanks again for everybodys responses
Professional Member*
I did one yesterday just as you described.
Professional Member
I get some like that (full of flaky black HX coating bits), but most of the ones I unplug are full of the same sort of slimy stinky brown mold/gunk that builds up in drain lines.
Professional Member
It seems like I run into this same problem on a lot of 90% L.P gas furnaces. The trap is usually filled with a black, slimy, soot-like substance.
Professional Member*
Please hook a manometer up to the pressure switch properly. You need to use a tee fitting on both sides of the pressure switch to see the differential, which will show you where your problem is. Unless your furnace is a 120 thousand btuhr, you should have that disc in the combustion air box, so your excess air isnt out of control
Professional Member
Why did the furnace work for 6 years with the baffle in place? Easy answer the restriction is someplace else and taking out the baffle is only a temporary fix until the secondary hx gets worse. I'm amazed how much help this homeowner got in this thread and he chose to ignore it and go with a bandaid fix.
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