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Old 12-19-2007, 04:37 PM   #1
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Pressure switch or control board?


I have a comfortmaker rpj2 in the house I bought a year ago...

So the furnace decides to go crazy today.
I am getting a flashing light telling me the Pressure Switch is stuck closed...

So I am doing various things I have seen on the net in different forums to check it.
First off the voltage is fine I checked it and both sides are at 26v on the pressure switch.

So I unhook the hose to the blower...I can actually see the rod move on this to make the connection on the back side of the pressure switch...

So I can see that when it's unhooked the rod moves out when it's hooked up it moves back into the pressure switch...
Was blowing in the hose and sucking air through the hose as well...and doesn't seem to be anything wrong there.

Well anyway If I unhook the hose then you get the pressure switch is open warning lights of course...And if I have the hose on it gives me that pressure switch is closed.

Now if I have the furnace running...and then take the hose off for a minute when I get the warning saying its stuck closed...and then I get put it back on I get the warning it's stuck open...when I put the hose back on after a minute the lights stop and the furnace ignites etc....

So here are my questions...
1) Is the blower for the plume or chimney supposed to always run when the furnace is on?

2) The switch seems to actually be working correctly unless I am missing something? Does this sound more like the controller board is bad?

I appreciate any help here since furnace guys are a killing here in price and I am not an HVAC guy obviously LOL...


Last edited by zerofill; 12-19-2007 at 04:39 PM.
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Old 12-19-2007, 05:08 PM   #2
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Pressure switch or control board?


K...the exhaust fan also won't kick off ever it seems...I turned the thermostat all the way down...
Is it possible that a bad thermostat could cause all this?

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Old 12-19-2007, 07:51 PM   #3
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Pressure switch or control board?


There are three terminals on the pressure switch, "C", "NC" , and "NO" . When the fan is off the "NC" and "C" should have continuity, when the fan is on the "NO" and "C" should have continuity. If that isn't what happens the switch is shot. The inducer fan should only run when there is a call for heat to the control board on the "W" terminal. If the inducer is running when the wire is removed from that terminal, change out the board.
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Old 12-20-2007, 04:34 AM   #4
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Pressure switch or control board?


Is it common or correct for it to signal high rollout and the flame to go out and then after about 5 minutes light goes out and flame reignites? Is this a safety cool down feature?
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Old 12-20-2007, 04:57 AM   #5
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Pressure switch or control board?


Quote:
Originally Posted by bigMikeB View Post
There are three terminals on the pressure switch, "C", "NC" , and "NO" . When the fan is off the "NC" and "C" should have continuity, when the fan is on the "NO" and "C" should have continuity. If that isn't what happens the switch is shot. The inducer fan should only run when there is a call for heat to the control board on the "W" terminal. If the inducer is running when the wire is removed from that terminal, change out the board.
Ok so I feel I am mistaken on what I took for the pressure switch and what is the actual pressure switch....

I assume the switch under the exhaust motor is the pressure switch? My first assumption was that the actual switch behind the diaphram was the switch?


So I am taking it that the little micro switch or whatever on the back of the diaphram where I marked "A" is not the pressure switch. "B" is the actual pressure switch?
C - Flame sensor
and "D" that you can't see cause its cut off is the high rollout sensor that looks similar to "B" but is right above the burners.

Am I correct in all this? Or am I completely off lol

Last edited by zerofill; 12-20-2007 at 05:34 AM.
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Old 12-20-2007, 06:11 AM   #6
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Pressure switch or control board?


So been playing with it forever again...
same stuff happens if I take the hose off for about 10 seconds put it on the furnace runs...and heats...
And seems to keep doing that...but if I turn the thermostat down the furnace doesn't ignite anymore but the exhaust fan runs forever...doesn't seem it will stop.
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Old 12-20-2007, 06:50 AM   #7
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Pressure switch or control board?


I have found that the control unit is a Model 50a50-110 and is made by white rogers...They have a new style that replaces this one. The new one is called 50A55-843. What is the best way to go about troubleshooting this board to see if it is the actual thing at fault? Or is it wise to change the pressure switch first? I imagine this damn board is expensive.

Here is a picture of the control unit in it:

Last edited by zerofill; 12-20-2007 at 06:53 AM.
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Old 12-20-2007, 07:36 AM   #8
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Pressure switch or control board?


Ok...
A - is the pressure switch
B - is the rollout sensor
C - is the flame sensor
D - I have no idea what it is for...

So... The pressure switch gets voltage and there is only 2 wires on mine. Voltage is around 26v

B - I took this heat sensor out and placed it by a torch to warm it up...it seems to work fine

C - Flame sensor thing seems to be fine...I don't think the furnace has any problem detecting a flame.

D - I do not know what that little sensor is?

Also the the exhaust fan always runs continuously...

So what should I check now? Is there anyway to identify a problem with that control board with a multimeter?
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Old 12-20-2007, 12:33 PM   #9
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Pressure switch or control board?


Just for future reference if anyone else has these similar problems...it was the controller....They cost about $117

There isn't much to these furnaces...you can check about 4 things and then its all in that damn controller heh.
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Old 01-31-2008, 09:33 PM   #10
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Pressure switch or control board?


I have the exact same problem, light flashes twice, the exhaust fan runs forever. Unplug PS and plug it back will kick the Furnace to work a circle.
I switched a good pressure switch from another unit to make sure it's not the PS problem. I am going to change the controller, where did you get it for $117?
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Old 01-31-2008, 09:36 PM   #11
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Pressure switch or control board?


Before you assume it's the control, check for a blockage in the flue piping, if the pressure switch is opening up and stopping the cycle it could be blocked in some way.
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Old 02-01-2008, 04:29 AM   #12
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Pressure switch or control board?


Security Supply...
Believe they are in a lot of areas...

And on mine I did check everything prior...
I will have to grab the number for the new unit...it has changed model numbers about 3 times to newer revisions...

But really...this furnace has about 4 or 5 things you can check and after that it's in the controller....not much to these furnaces. Actually the price for the controller was $96 from there. I will try to post it later tonight...5:30am here bed time hehe.

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