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spitracer 01-29-2010 12:46 PM

Amana 90% Furnace Problem - kok328 help?
Here my problem, we get back from vacation and the wife says whats that noise....what noise....the noise from the furnace...crap, I'll go find out.

Get down to the furnace and the Inducer Blower Motor has pounded out it's bearings, at least thats what I figured as it was vibrating. Next day I replace the blower with the correct model. I tore the old one apart to see if it was repairable and see the plastic cage has broke and wore through the plastic housing...WOW!

So install the new blower and turn the furnace on, goes through the proper sequence and after flame ignition the pressure switch shuts the gas off after about 6 sec. I figure the flame sensor needs to be cleaned so I pull that out and steel wool it per the manuf. recommendations. Reinstall and same thing happens plus I look for the flashing code and see 3 flashes...pressure switch code. Again from the manual it can be the intake or exhaust air, wiring or bad switch. The furnace has been running fine before we left and as my house sitter didn't notice anything wrong with the heat so I don't think the intake and or exhaust has been clogged.

So I decide to buy a pressure switch, installed it and the furnace ran for 5 min. or so, so I figured it was fixed and went back to work. Came home to no heat. Went down recycled the furnance and watched after 10 min or so the flame goes out and I get a 3 blink error code.

Now this is where it gets goofy. I removed the flame box cover and recycle the furnace, gas goes on and furnace works long as the air tight cover isn't installed. So this leads me back to the intake/ exhaust air, as my piping goes up thru 2 stories and it's winter in Michigan and I'm no mountain goat I cut my intake pipe and use my shop debris is sucked down the pipe and the inducer motor doesn't appear to be having any problem and I can hear the exhaust when standing outside.

I plan on putting back on the cover and leave the 3inch PVC furnace pipe unconnected to the stack. I assume if I don't have a problem then I must have a plugged intake stack, If I still have a problem...I HAVE NO IDEA WHATS WRONG (this is what I expect).

Other possibilities:

New Inducer Blower is sucking to much air for the long intake stack to supply to the furnace and having the lid off the box helps make up the missing air?

Flame roll out sensor is bad...but don't get the correct code??

Flame sensor is bad, but likes the extra air????

I just find it hard to believe the inducer motor doesn't have something to do with this as it is the only thing that has changed in the past 12 years! but it is the correct model and seems to be running correctly and all the vacuum lines are hooked up.

Any suggestions would be appreciated.


kok328 01-29-2010 07:37 PM

Well, this is what I can tell you.
I assume that you replaced not only the blower motor but, the housing and impeller too.
I have seen one inducer motor in my time that was running but, not at enough RPM's to "make" the pressure switch relay. This will be hard to verify, I was lucky enough to have two like units side by side to tell me this.
Also, there is no intake stack, just an exhaust stack. The intake the your referring to would be a fresh air intake for combustion purposes on a high-efficiency model furnace. The intake for the inducer fan is the actual combustion chamber of your furnace. The inducer fan evacuates the gas prior to ignition otherwise the unit could explode. Once the unit is up and running the inducer exhausts the burned gas to prevent CO2 build up during combustion. So the things to check here would be: verify that you don't have a blocked exhaust stack, verify that you don't have any leaks (cracks/holes) or blockages in the tubing that runs from the inducer housing to the pressure switch. Make sure the new inducer housing is sealed air tight to the combustion chamber. Also check the leads coming out of the pressure swith to see if continuity is being achieved at the pressure switch when the inducer motor is running. If this checks out, I would suspect the relay that attaches to the pressure switch which must be "made" to allow for ignition. This could be falling out during the run cycle and causing a premature shut down of the system and/or failure to ignite. Post back if you still need help and haven't froze to death by now and/or been forced to called a contractor.

spitracer 01-30-2010 01:14 PM

KOK appreciate your comments!

The furnace is working correctly as long as the burner box cover is off. It has run a day and half with no issues.

I thought I would experiment to see if the intake stack was actually clogged and since the air intake stack was cut so we could suck anything that might have blocked it I put the flame cover back on and allowed the furnace to suck air through the cut pipe that was open to the furnace room.

I figured if the furnace stayed lit then the stack was still obstructed. After about 10 minutes....out went the flame.

I have checked all the flex cracks or blockage, the inducer blower was an entire assembly and the pressure switch and diaphram were replaced.

So the question is why will the furnace run when the flame panel is off? and is it really danagerous to have this cover off? I do have the outer cover on the furnace.


kok328 01-30-2010 03:58 PM

This is really weird. It sounds like the inducer system (inducer, pressure switch, hoses and relay) are all functioning properly. By chance was the inducer impeller installed backwards. This would be really bad as CO2 is being pumped INTO the the home instead of being pumped OUT of the home. Potentially, you may have a problem with the burner box cover being left off as the inducer motor may have problems exhausting all the CO2 created by the combusted gas. It could also be that the inducer can create enough draw without the burner box cover being on but, I would think that just drawing in furnace room air instead of outdoor air would be enough. Again, the fresh air intake is for combustion purposes and shouldn't affect the inducer system. However, what happens when you reconnect the intake stack with the burner box cover removed?
Another thought is that you have mistaken the exhaust stack for an intake stack and if it is blocked, the inducer won't build enough vaccuum or pressure to close the pressure switch relay. This is might explain why the system won't run without the burner box cover plate installed as it needs somewhere to relieve the exhaust pressure. This is a very dangerous condition as you would definitely be exhausting CO2 into your home.

spitracer 01-30-2010 08:26 PM

The inducer assembly is a sealed unit, so I doubt anything is seriously amiss with the unit. I will pull the inducer tomorrow and use the shop vac on it. We did go outside and can hear the exhaust gas leaving the pipe but that doesn't mean it isn't partially blocked.

When I pulled the damaged inducer motor I noticed a 1/2 wide very thin (almost tin foil) twisted metal comming from the outlet (exhaust) port. I did pull it out a couple of inches thinking it was something that had blown thru the furnace. I have been told it is part of the furnace to help the exhaust gas leave the furnace? I did work it back into the exhaust hole .... but maybe it is partially blocking the outlet when I pushed it back in????

Thanks again.


spitracer 02-03-2010 08:27 AM

Status update for anyone thats interested.

My temp fix of leaving the flame cover door off stopped working last night. I took the flame sensor out and sanded it with emmory(sp) cloth, I also removed the inducer blower one more time and put the shop vac to the exhaust pipe....nothing was restricting the pipe. After these two items were done I refired the furnace and it appears to work OK....with the flame cover off. I wasn't up to messing with it anymore so I didn't try to reinstall the cover and see what happened.

I did order a new flame sensor and will install tonight, I'm hoping that this solves the entire issue....will see!

spitracer 02-04-2010 07:11 PM

It's official I'm beaten.

I replaced the flame sensor and also talked with a tech. He determined that when they installed the furnace they failed to install the inducer blower drain so that it terminated beneath the water level so that it wouldn't impact the pressure switch by allowing oxygen back into the drain? Anyways I changed that as well.

So made these changes installed the flame box cover and fired the system up. It ran for 20 min or so and out went the flame and the pressure switch code started flashing. :confused:

Like I said I give up. Tomorrow I'll call in the tech's.

kok328 02-06-2010 08:04 AM

Don't give up so easily, it's just a furnace.
Are you metering the unit when it falls out?
This will tell you what's being made, tripping or limiting.
Where in MI are you located?

spitracer 02-06-2010 09:18 AM

I'm in Jackson.

I talked with an Amana tech Friday and he gave me a new gasket for behind the inducer motor which I will install tonight. He also wants me to check the PVC pipe to make sure it hasn't slipped and a pocket of water has formed and during the run cycle it doesn't start to fill up with water and shuts the pressure switch off......long shot at best.

I do believe the pressure switch is dropping out. The other thing the tech said to do was start the cycle with the press. switch in play then unhook it and use a jumper wire between them. If the furnace stays running (this is with the cover on the flame box) then it indicates it isn't an exhaust issue, if it drops out then it is something electronic....I believe this is what he indicated.

The inducer motor drain doesn't continously make water during the run cycle, once the cycle has finished then the drain dumps out a couple of ounces or so (never measured it to be exact).

Will see if the gasket makes any difference.


kok328 02-06-2010 11:53 AM

The pocket of water is normal. It's cold out and the CO2 and warm air is condensating in the exhaust stack and dripping back down. I was going to suggest to jumper the pressure switch relay but, didn't want to take responsiblity for CO2 backup into your home, not being 100% if you were exhausting properly. It really sounds like a clogged exhaust stack as most moisture would be exhausted with some (little) vapor dripping back down. In addition, with the flame box cover off, it give the inducer somewhere to pump the CO2 (unfortunately this is going into your home). Again, the inducer pressure/vaccuum satisfies the pressure switch which in turn closes the relay to allow for ignition and continued run of the burners. If jumpering the relay allows the system to run and your inducer circuit (blower, motor, press. switch and relay) are all new then it has to be the exhaust stack or a faulty circuit board. The fact that it will stay running with the burner box removed tells me it's not the circuit board. Hook up your ohm meter to the pressure switch relay and run the system and take note of your ohms when the system drops out. Worst case is you might have to go up on the roof and check for blockage of the exhaust. If there aren't any elbows in the system you could tie something heavy to a string and drop it down to see if it comes out the other end into the inducer compartment. Of course you'll have to remove the inducer motor housing to see this.
P.S.- I'd love to help but, too far to drive for me, plus it's freezin out - LOL

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