RPJ II furnace with draft motor constantly on


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Old 11-22-07, 08:52 PM
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RPJ II furnace with draft motor constantly on

Hi all,

I've got an induced-draft furnace, and the blower motor is constantly running. It seems the control module isn't happy about that, and wants to see the pressure switch go from open to closed before starting the cycle (confirmed by disconnecting and reconnecting the wires to the pressure switch, which will start a cycle).

Unfortunately I'm not at home and can't recall the model of control module (something-90). I guess the short version of my question is, is there likely to be a relay for the motor that might be stuck open, or is the board fried and needs replacement? If it's the board, any WAG as to how much they typically go for?

Thanks,
Andy
 
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Old 11-23-07, 09:20 AM
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If your form of ignitor never even tries to come on (check that aspect out), good chance then the pressure switch is not proving the necessary pressure for various reasons, like poor venting, or too much condensate water hung up inside, or cracked heat exchanger, or vacuum line loose or broke, or bad proving elelctrical switch on the inducer (not all furnaces have these) or the pressure switch itself is bad. Or maybe something like a rollout switch in the low volt circuit has tripped out.

Have you tried this test so that you know that it indeed is with the pressure?: By say sucking on the vacuum tube to the pressure switch and while doing that you then squeeze off the line, to see if the furnace fires up?, or at least makes it to the ignitor function stage, if it wasn't even getting to that stage before?

If you are able to get the furnace to go by doing any test with your furnace by say jumpering wires to safety switches on the low volt circuit, or by that test I mentioned, it's definitely not your board. One only wants to suspect and replace a board after everything else checks out good.
 
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Old 11-23-07, 04:23 PM
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Sorry I wasn't more clear, but yes, the furnace mostly works. There's a code of 2 flashes, which on mine (and apparently some others) means "pressure switch contacts closed". The furnace really wants to see the pressure switch transition from open to closed before firing up. If I fool it into thinking that's happening, either by disconnecting and reconnecting the vacuum hose, or the electrical circuit (since the draft-fan is always running, either of those will open the circuit and then close it again), the furnace will run for a cycle, and then when it would normally turn the induced-draft fan off, it doesn't.

So I guess I need to know what would be a likely reason that the induced-draft blower would always be running.

Thanks,
Andy
 
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Old 11-23-07, 04:29 PM
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But your furnace should totally fix itself (stop inducer from just running for no reason) if you fix the pressure detection problem. Maybe the plunger connected to the pressure switches diaphram is sticky, as one example. Pressure switches are EXTREMELY sensitive and any subtle deviation can be the difference between the plunger moving it's whole required distance to complete the contacts, or not.

The fact you can fiddle with this and get it to work on disconnect/ reconnect, shows something is up here.
 
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Old 11-23-07, 04:33 PM
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That'd be nice, but it doesn't.

As far as I can tell, the switch works fine. If I remove the hose from the inducer, and suck on it, I can see and hear the switch closing. I tested it with an ohmmeter, it shows no resistance while in the "closed" position, and infinite while in the "open" position, all of which says to me that it's working. What isn't working is whatever part of the furnace is in charge of running the inducer in the first place, and strangely enough, it's stuck on instead of stuck off.

And if I do the above test while the thermostat calls for heat, the control module sees the pressure detection circuit go from open to closed, it's happy, and it fires up the burners. Then they run for a normal cycle, and the next cycle won't start, because the inducer is still running.

That's what lead me to suspect the control module...

Andy
 
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Old 11-23-07, 05:01 PM
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With your furnace, if you suck on the hose, and then crimp the hose while doing so, then does the furnace fire up? (You may have already stated this, but I'm moving along quickly here). This should not be this tough a problem.

I presume you have one pressure switch. Do you only have one vacuum tube to it, but have *3* low volt wires to it?, where, as you suspect, the other set of contacts must be closed first to get the furnace to first start up, and then once it starts the ventor, then the vacuum develops in the furnace and hence the tube causes THOSE contacts to open and then close the other contacts to allow the ignition cycle to take place?

If all this is so, then it could mean the points inside the vacuum switch are bad for the two contacts that must be first closed to get the furnace to start (IOW, bad pressure switch even though the other half of the switching is good). If you have the 3 wires, have you tried your ohms test involving all 3 wires to see if the shift can take place, between terminals 1 and 2 and 1 and 3 (with 1 being the common)? I.e., when 1 and 2 are open, 1 to 3 should be closed. And when 1 to 2 are open, 1 to 3 should be open. Does this occur?
 
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Old 11-23-07, 05:07 PM
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To answer your first question: I doubt it, but I'll try it when I get home. To get it to start, I do the opposite. Remove the hose from the inducer (thus opening the circuit) and replace it (thus closing the circuit). Now the furnace sees what it would normally see (blower off = no vacuum in draft = open circuit, then switches to blower on = vacuum = closed circuit), and is happy.

I only see one pressure switch, but it only has 2 wires. I assumed it's entire purpose was to let the control module know that the inducer was indeed inducing, so the rest of the cycle can proceed (which it does, if I fake it as mentioned).
 
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Old 11-23-07, 06:17 PM
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This should be easy then!

We already know that when you suck on the line, you can make the contacts close to get no resistance = good.

But now we have to determine if the switch is at fault due to tiny leak in the diaphram (you can overcome the leak with sucking it you know, so that test can really be an inconclusive fooler).

But what is not a fooler is this: First suck on the line to make the contacts close; then hold the tube pinced and also put finger over end of tube long enough to determine if it bleeds down to cause the switch contacts to open. If it does, either you are not doing a good job or you have just proven the switch is bad, and not the venting of the furnace. Conversely, if the switch stays closed during the test, then you know you have a venting problem.
 
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Old 11-26-07, 10:26 AM
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Thanks again...

I'm more than willing to keep up this testing, although I think I need to reiterate another point:

The inducer runs ALL THE TIME! It didn't used to. When the furnace is powered on, regardless of whether there's a call for heat, the inducer is running. This includes the very first time it's switched on, and no cycles have happened yet.

I've watched the pressure switch as well, and it seems to stay closed while the inducer is running, so I really do think the pressure switch is 100% OK.

Does that make any more sense?

Thanks,
Andy
 
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Old 11-26-07, 12:41 PM
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The inducer is SUPPOSED to run before anything else cycles.

So you are back to square one as far as proving if the inducer is really good. As mentioned, if you suck on the vacuum tube and get the furnace to work, all you have really proven about the pressure switch is that the contacts in it are good. But if there is a diaphram leak, your extreme suction will temporarily over come that, and fool you into believing the pressure switch is good.

That is why you have to suck on it some and pinch it off and do a bleed down test on it. It should not bleed down no matter how long you have it pinched off. If it does, the diaghram in the pressure switch is bad.

The suction through that vacuum tube is extremely tiny. Very little suction. Because of that, just the slightest hole or tear in the diaphram will make it so the contacts do not close, and then the only thing that will run is the inducer motor.

Yes, it's possible the pressure switch is good. But you have to veryify it by this means. If the switch is good, then you can move on to why the suction through the furnace is not up to snuff.
 
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Old 11-26-07, 03:12 PM
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True enough, but it's not supposed to run all the time, which it currently does, and it didn't used to.

I really do appreciate your efforts to help, but it comes down to this:

1) If I can get a cycle started (which I can, by faking normal operation of the inducer), it keeps going. That means, to me, that there's no leak in the pressure switch.

2) If I set my thermostat to run the circulation fan only, and turn the heat off, the inducer fan will run. How do I fix that?

As I said before, this is not the same behaviour that the furnace used to exhibit back when it "worked." What it used to do was:

- when the t-stat called for heat, the inducer would start
- some short time (10-15s) later, the burners would fire up

Now, since the inducer is always running, when the above cycle starts, the furnace has no way of knowing that the pressure detection circuit is working, so it gives an error code of "pressure switch contacts closed" (which they are!), and won't start a burn cycle.

Thanks,
Andy
 
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Old 11-26-07, 04:21 PM
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Hi Andy:

Tell us about your thermostat. What is the model # of your furnace?
 
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Old 11-26-07, 05:13 PM
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Originally Posted by amason View Post
1) If I can get a cycle started (which I can, by faking normal operation of the inducer), it keeps going. That means, to me, that there's no leak in the pressure switch.
You mean to tell me that once you suck on the line, and then stop sucking, the flame will stay on and all is okay, til the next cycle?

And if so, do you get the vacuum line plugged back in right away after you suck?, or do you just let it dangle?

I'm not sure of your response yet to the above, but at the moment, now I'm leading towards dirty/pitted contacts that your suction creates better contact in the pressure switch's points and once this good contact is made, it keeps going.

You see, the pressure switch has to keep maintaining "proof". That is the idea of a safety pressure switch! You CAN'T just fake a pressure switch to keep running. But since YOU are, this says to me that your suction force, that is greater than the furnace's suction force, is driving those points together harder than by natural occurance, and once electrical contact is made, the electricity keeps the contacts 'glued' together. (Electricity is good for doing that.)
 
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Old 11-30-07, 11:48 AM
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Hmm, how to put this nicely when I'm tempted to be exasperated, and yet I'm asking for your collective expertise with nothing in return...

The vacuum switch is fine, just fine. The hose is fine, the vacuum is fine, everything's fine, except:

The inducer runs all the time. The inducer never stops running. When I power the furnace on, the inducer starts immediately, even with the t-stat set to off. Then it never ever stops. You know, I actually didn't check what would happen if I also set the circulation fan to auto on the t-stat, but if I had to guess, I'd say the inducer would probably run. I didn't do that because it wouldn't really matter anyway, what matters is:

The furnace needs to see the pressure switch open most of the time, and then close when the inducer starts, otherwise it can't know that it doesn't have a switch that's stuck closed. Since the inducer is already running, the switch is closed. Because the switch is already closed, I get a fault code of "pressure switch contacts closed."

For the THIRD time (oops, exasperated there, sorry): If I fake correct operation of the inducer*, either by disconnecting the electrical circuit for the pressure switch, then reconnecting it (so the circuit goes from open to closed before a burn cycle), or by disconnecting the vacuum hose from the inducer, then reconnecting it (so the circuit goes from open to closed before a burn cycle), I will get a full, lovely, warm, burn cycle. Then, because the inducer fan is still running, it won't happen again, and I'll be cold and unhappy. Stupid inducer fan.

*which is: at the start of a call for heat by the t-stat, the inducer should start, the pressure switch should close (letting the furnace know that the draft is working, which it is), then the burners should start

So, how do I stop the inducer from running all the time? Is there typically a relay for it that could be stuck closed? Is my control board fried? How much is a control board for your average induced-draft furnace?

daddyjohn:

Thermostat is a fairly generic Honeywell programmable. I see them all over the place. There's no model number anywhere obvious, but under the battery cover is this:
T8132A1007 1
9440
It's not newly installed, and as far as I can tell, it's working fine.


The furnace is an Inter-City Products Corporation, Model #
GNI080A012DIN, and has RPJ II on the top left of the bottom cover.

Thanks,
Andy
 
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Old 11-30-07, 12:00 PM
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Originally Posted by ecman51` View Post
You mean to tell me that once you suck on the line, and then stop sucking, the flame will stay on and all is okay, til the next cycle?
No, that's not what I'm doing. I actually have to STOP the inducer motor from sucking on the tube, then plug it back in so it can start again. Once I do that, everything runs great.

Originally Posted by ecman51` View Post
And if so, do you get the vacuum line plugged back in right away after you suck?, or do you just let it dangle?
Hmm, I was going to say you could think of it like plugging it back in right away, but that isn't really the problem. The problem is that the furnace starts sucking on the hose and closes the switch before it's supposed to.

Originally Posted by ecman51` View Post
I'm not sure of your response yet to the above, but at the moment, now I'm leading towards dirty/pitted contacts that your suction creates better contact in the pressure switch's points and once this good contact is made, it keeps going.
As I said, I don't think that's it, since one of the ways I can make it work is to simply disconnect and then reconnect the hose. After plugging it back in, everything works fine, so that tells me that the switch itself, and the vacuum assembly that actuates it, are fine.

Originally Posted by ecman51` View Post
You see, the pressure switch has to keep maintaining "proof". That is the idea of a safety pressure switch! You CAN'T just fake a pressure switch to keep running. But since YOU are, this says to me that your suction force, that is greater than the furnace's suction force, is driving those points together harder than by natural occurance, and once electrical contact is made, the electricity keeps the contacts 'glued' together. (Electricity is good for doing that.)
Now we're getting close. I see your point. However, part of the safety aspect is self-checking, and this furnace wants to know that the switch is working. Since it's always closed (due to suction from the inducer actuating the switch), it doesn't look to the furnace like the switch is working, so it won't burn.

Andy
 
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Old 11-30-07, 06:26 PM
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Originally Posted by amason View Post
No, that's not what I'm doing. I actually have to STOP the inducer motor from sucking on the tube, then plug it back in so it can start again. Once I do that, everything runs great.

What if you leave the hose connected and just shut off the furnace to stop the inducer, and then turn the furnace back on? Won't it start up then?
 
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Old 11-30-07, 09:39 PM
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from the sounds of it the contactor is jamed shut not allowing the vent motor to shut off causing a fault in the vac switch to show a closed state on call for heat. would cause an error and lock out the gas valve and ignition until the furnace had the error code removed. like shutting down or stopping the motor from running
 
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Old 11-30-07, 10:05 PM
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in other words, at this time i have reason to believe your intigrated control board will need replacing
 
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Old 12-01-07, 12:44 AM
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Originally Posted by ecman51` View Post
What if you leave the hose connected and just shut off the furnace to stop the inducer, and then turn the furnace back on? Won't it start up then?
Unfortunately no, that doesn't do it. The inducer really does come on immediately on power-up. Because of that, the switch is already closed (too early) so the burners won't start. This leads me to believe that the control board needs to see the circuit open before a call for heat, and switch to closed sometime shortly after.

Andy
 
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Old 12-01-07, 12:53 AM
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Originally Posted by LaBait View Post
in other words, at this time i have reason to believe your intigrated control board will need replacing
Makes sense to me...

Could anyone take a wild guess as to how much that might cost?

Thanks,
Andy
 
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Old 12-01-07, 03:57 AM
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Originally Posted by amason View Post
Makes sense to me...

Could anyone take a wild guess as to how much that might cost?

Thanks,
Andy
LOOK---I'm not going to pretend that I am familiar with that particular furnace, but are there DIM switches on the board that may have been moved, maybe by accident, to allow a 'prepurge cycle' or 'constant on' of the inducer????? Many manufacturers use one board for several models of furnaces and the DIM switches permit them to do so by offering some flexability in application. Also, perhaps the board may have been replaced with a generic and maybe the DIM switches may have been moved? If the unit does have DIM switches try to determine which should be the correct position by referring to the manual. Also, BEFORE moving anything, write down their position! I have had trouble with boards with DIM switches and sometimes they are in the correct position and the contact (I guess) grew weak over time, so I moved them back and forth a few times, put them back where they were, and presto! It works again. Hope you have the same luck. If the board does not have DIM switches I just wasted 10 minutes and could have made coffee by now. GOOD LUCK! Charlie
 
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Old 12-01-07, 09:14 AM
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Originally Posted by amason View Post
Makes sense to me...

Could anyone take a wild guess as to how much that might cost?

Thanks,
Andy
Sorry but i would have no idea as to what that would cost in your area, best thing to do is to contact a seller in your area and price it out. and furnace to furnace the boards vary in range quiet a bit. seen them as low as $80 and go all the way up to around 500
 
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Old 12-01-07, 09:17 AM
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Originally Posted by ecman51` View Post
What if you leave the hose connected and just shut off the furnace to stop the inducer, and then turn the furnace back on? Won't it start up then?
this would not work because the board would sence a closed switch on start up and do a lock out, the only way you could get that to work is to unplug the enducer moter (vent motor) to allow the code to leave the board, then plug it back in on a call for heat
 
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Old 12-01-07, 05:14 PM
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Quick update:

I think I made it worse. I checked DIP switches, moved them all back and forth (back to original positions), and powered the whole furnace down at the breaker. When it came back up, the inducer was off (and I thought I'd fixed it), but no such luck...

Now it flashes 3 times, meaning "pressure switch contacts open", presumably because the inducer doesn't start.

Oh well. If the control board is the only thing that controls the inducer, it looks like I'm ordering a new one. Found a replacement at http://arnoldservice.com/control_boards.htm for $115, not too bad.

That page says that a 50A55-843 doesn't replace a 50A55-113, whereas the on the White-Rodgers site it's the suggested replacement:
http://parts.white-rodgers.com/commo...MD=DisplayInfo

Incidentally, on that page I found the installation PDF, which has some great background on how the furnace control is supposed to work, and what it should do in various failure modes. Also lists the DIP switch setting, none of which have to do with the inducer, only with the circulation fan.
http://www.white-rodgers.com/wrdhom/.../0037-6265.pdf

Thanks all,
Andy
 
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Old 02-08-10, 03:01 PM
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Very late update:

I bought a control module and installed it. Problem solved. So I thought I'd post to say that there are things that can go wrong that aren't covered in the troubleshooting guide for the control module.

Thanks,
Andy
 
 

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