Furnace Problems (Pressure Switch Stuck Open)

[Mar]

Help me be a furnace repair man! This is my second issue with this furnace but first in over 5 years. I cam home from work and it was really cold in the house, the light on the furnace is flashing 3 times which corresponds to "Pressure switch open, should be closed" on the inside of the panel. I turned off the breaker and when I turn it back on, there's a hum for 30 seconds, then it goes into the 3 error code every time.

I unhooked the vacuum hose from the inducer and sucked on it to close the pressure switch while it was humming and the furnace fired right up, except the flames shot out towards me instead of firing into their little tubes. I'm guessing there was no pressure to suck the flame in so it just ignited anywhere.

Do I need a new inducer?

[redblack]

Yes

[Mar]

Where do I buy that? Rona?

[dj_rice]

Yes

[Maxx Mazda]

A Mar thread that's resolved in less than 300 posts???

[rx7_turbo2]

Originally posted by Maxx Mazda
A Mar thread that's resolved in less than 300 posts???

Easy now, it's not resolved yet

[Mar]

I know, I'll entertain you guys later, I got a serious problem right now.

I pulled out the fan motor (inducer?) and blew it out with canned air but nothing came out of it. Then I spun the wheel inside it but that seemed to turn without any resistance. Then I put it all back together and tried it again, it seemed like it was going to expire the 30 second wait again but after about 25 seconds the fan SLOWLY started to spin and then the 30 seconds timed out and it stopped.

I flicked the breaker again, this time the fan started immediately and the furnace fired up with flame but shut off again after a few seconds. I left it and it tried again with the same result. I still left it and it tried again, this time it has been on for over 5 minutes and the house is heating up!

More symptoms of a bad fan / inducer / motor thing?

[Crazyjoker77]

Originally posted by Mar
I know, I'll entertain you guys later, I got a serious problem right now.

I pulled out the fan motor (inducer?) and blew it out with canned air but nothing came out of it. Then I spun the wheel inside it but that seemed to turn without any resistance. Then I put it all back together and tried it again, it seemed like it was going to expire the 30 second wait again but after about 25 seconds the fan SLOWLY started to spin and then the 30 seconds timed out and it stopped.

I flicked the breaker again, this time the fan started immediately and the furnace fired up with flame but shut off again after a few seconds. I left it and it tried again with the same result. I still left it and it tried again, this time it has been on for over 5 minutes and the house is heating up!

More symptoms of a bad fan / inducer / motor thing?

Chances are its the actual pressure switch itself since it sounds like you've verified the inducer motor is working.

[Mar]

Originally posted by Crazyjoker77


Chances are its the actual pressure switch itself since it sounds like you've verified the inducer motor is working.

The motor wouldn't spin the fan the entire day. It only started spinning once I took it all apart and spun it with my hands.

[ZeroGravity]

I had similar problems once, but I wasn't man enough to take it apart myself. Called for furnace repair, changed out a couple of parts still similar issue. Clear the code, furnace runs for a short time, furnace cuts out, and the code came back.

The last "straw" that "fixed" the problem was that I changed my 3M filter. So somehow, from the looks of it, the 3M filter got moisture on it and the "paper" part got harden after it dried. So not enough air is getting pulled in. And the furnace stops.

The parts that were changed out probably contributed to the fix... I hope. At least that's what I'm trying to make myself to believe that after all the waiting for parts and money paid.

[Mar]

Where do I find the filter? Do you mean the big furnace filter I change monthly? How would it get wet?

[ZeroGravity]

Originally posted by Mar
Where do I find the filter? Do you mean the big furnace filter I change monthly? How would it get wet?

Yes, the furnace filter. I change mine every 3 months (those 3M paper like core filter that goes on sale at costco every so often). I don't know how the filter got wet or where it picked up the moisture. But it did. And after it dried, air doesn't flow through it that well.

[mr2mike]

Mountain out of a mole hill coming along great, Mar.

The diagnostic lights generally don't lead you astray. Change the pressure switch out.
Or pre-emptively start the thread, "How do I thaw out my water lines without them bursting?"

[eblend]

Originally posted by Crazyjoker77


Chances are its the actual pressure switch itself since it sounds like you've verified the inducer motor is working.

From the sounds of it, it's actually the inducer motor? If the motor isn't spinning, it isn't generating suction, and thus not kicking off the pressure switch. Pressure switch won't kick off if inducer motor is not going, it relies on the motor spinning to get suction and close.

[CLiVE]

Carrier furnace? Had similar issues to what you described. Changed the pressure switch. Works great. Also drilled out the tube slightly, as per this video. So the condensate doesn't build up and block the tube.

https://www.youtube.com/watch?v=iT__bzNcaoQ

When you sucked on the hose of the pressure switch, does it make a loud click in both directions, or just one? Mine only clicked in one direction.

[Mar]

Originally posted by eblend



From the sounds of it, it's actually the inducer motor? If the motor isn't spinning, it isn't generating suction, and thus not kicking off the pressure switch. Pressure switch won't kick off if inducer motor is not going, it relies on the motor spinning to get suction and close.

That's what I thought.

Originally posted by CLiVE
Carrier furnace? Had similar issues to what you described. Changed the pressure switch. Works great. Also drilled out the tube slightly, as per this video. So the condensate doesn't build up and block the tube.

https://www.youtube.com/watch?v=iT__bzNcaoQ

When you sucked on the hose of the pressure switch, does it make a loud click in both directions, or just one? Mine only clicked in one direction.

Both.

[Mar]

New blower installed yesterday, problem seems fixed. It isn't howling like a banshee any more.
The blower was $343, what a rip.

[Maxx Mazda]

Cheaper than a new Veloster...

[revelations]

Originally posted by Maxx Mazda
Cheaper than a new Veloster...

Or parking in a bike lane.

[jeffh]

Sounds like you replaced the inducer fan, not the blower fan. Good to know what those things cost, I always thought they were around $250