Carrier 9200 furnace, warms up but doesn't come on, 31 blink code


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Old 11-24-10, 03:30 AM
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Carrier 9200 furnace, warms up but doesn't come on, 31 blink code

My 12 year old Carrier 9200 furnace works most of the time. When it doesn't work, it makes the usual noises like it is going to come on, and then just stops with a 31 blink code--the fan does not come on. The 31 blink code translates to:

"Pressure, draft safeguard, aux-limit (when used), or blocked vent shutoff (when used) switch did not close or reopened. If open for longer than 5 minutes, inducer shuts off for 15 minutes before retry. Check for:

-Defective inducer motor or startup capacitor.
-Defective pressure switch or connections. If it opens after trial for ignition period, blower will come on for 90 second recycle delay.
-Low inducer voltage.
-Disconnected or obstructed pressure tubing.
-Proper vent sizing and condensate pitch or sag.
-Vent restrictions or high winds.
-Inadequate Combustion air supply."

After doing some testing I am suspecting the pressure switch (PS).

I measured across the two wires going into the pressure switch when the furnace was trying to come on, and found that it was closed (dead short) most of the time. I wasn't sure if my probe was making proper contact with the PS connections, since as I was doing this the furnace made one or two clicking noises and the fan came on with no heat. It then went off a few minutes later and came back on with heat after that.

I removed the pressure switch from the furnace (after turning the power off) and found that if I sucked (or blew I forget which) air from one of the hoses while plugging the other opening, that the switch would close--and if I plugged both holes after doing this that the diaphragm would slowly release and the switch would open.

Is this normal? Or should the diaphragm hold the switch closed with both holes plugged?

I reinstalled the pressure switch and the furnace has been working fine for the past few hours.

I was also very surprised to find a cheap microwave switch in my $2500 92% efficient furnace.
 
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Old 11-24-10, 08:38 AM
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Furnaces don't just start. A series of events has to happen which climaxes with the burners lighting and the fan switching on to circulate warm air.

That sequence of events starts with the circuit breaker in the breaker box being on and the wiring to the furnace being good and the power switch for the furnace being on. Once the power gets to the furnace, the fan compartment door has to be on so that the door switch is pushed in.

At that point, you can test to see if you have 24 VAC between the "C" and the "R" terminals. If you do, the transformer and any fuses and often other controls are working properly.

Then test for 24 VAC between C and W. When the thermostat calls for heat you should get 24 VAC at that point and the inducer fan motor should start up and stay on reliably.

Since from your post the inducer motor isn't starting and staying on reliably, you need to check that out.

Let's suppose for a moment that the inducer motor bearings have failed and it wont start properly and reliably. Were that the case you'd find 120 VAC being applied to the inducer motor and the 3-1 blink code, since the circuit board would be applying power properly and expecting the inducer motor to switch on and the pressure switch to close.

But if the inducer motor isn't operating properly that wont happen.

So you need to check things out to that point before going further.
 
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Old 11-24-10, 12:48 PM
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I guess my English wasn't clear: The inducer fan motor is starting up. Everything is normal until just before the blower fan is supposed to come on, then the furnace just turns off with the error code 31 showing.
 
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Old 11-24-10, 12:58 PM
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Sorry, but your description of symptoms is vague.

You need to describe in detail what is happening or we really can't be of help to you.

Calling something "normal" is a conclusion, not a description.


Here's someone who gave an excellent description of how their furnace was operating. That makes it possible to start zeroing in on the problem:

http://forum.doityourself.com/gas-oi...-problems.html
 
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Old 11-24-10, 10:43 PM
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The furnace is now working, so I will give you a better description when it fails next time. Thanks.
 
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Old 11-24-10, 11:16 PM
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The Carrier 3-1 diagnostic code is displayed when the pressure switch opens or fails to close when it should. That will prevent the burners from turning on or shut the burners off if they are lit.

I'd use an AC voltmeter to verify that the pressure switch is what is shutting off the burners. Connect one test lead to chassis ground and use the other to check for 24 VAC. One side of the pressure switch should have 24 VAC whenever the thermostat calls for heat.

The other connection should have 24 VAC switch on as soon as thye inducer motor comes up to speed. If that voltage is going to zero when the burners shut off, report that observation.
 
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Old 12-05-10, 07:28 AM
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Hey everyone,
I'm getting the same error 31 code on my carrier 92 furnace.

The first thing I tried to do was check the exhaust pipe to make sure nothing was in it to restrict the flow, it has a few pieces of shingle gravel.
Still received error 31

I removed the blower motor from the furnace and cleaned out all around it, I put new sylicone on it and put it back together.
Still received error 31

I changed the furnace from a single intake manifold to a dual intake manifold.
Error 31 went away for a month, now its back again.

So at this point I'm starting to think its an issue with the Pressure switch, so I took the hose connected to it and slightly blew back and forth, and I can hear it actuate, so I don't think thats the issue. Following the hose up from the pressure switch it comes to a T one hose goes to the intake manifold the other goes to where the Natural Gas comes in. When I disconnect the hose to the intake manifold the furnace will run, once I reconnect the hose the system will return to the error 31 and it powers down. I tried cleaning the intake manifold to remove any dust/dirt that might cause the error but I still get the code 31 when that hose is plugged in. One odd thing I should mention, is when I do the pressure switch check using the hose connected to the T (Still connected to the natural gas regulator thing) I can smell Natural Gas. Could it be that part is going out? Or should I focus on the intake manifold?

Thanks so much for your help
 
 

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