Bryant 395CAV Intermittent Heating Problem

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Old 12-23-08, 10:32 AM
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Question Bryant 395CAV Intermittent Heating Problem

I have a Bryant 395CAV024070 Gas Furnace that is giving an error code 31. I have checked the filter, condensate drainage, and all venting. The pressure switch has been replaced and I am still receiving the error code 31. I can sometimes get the furnace to work but sooner or later once it shuts down it will not fire back up and the blower motor will be running and never shut off. The thermostat will display AUX Heat On when this happens. I am getting ready to order a new manual reset limit switch but wanted to see if anyone might have an idea first.
 
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Old 12-23-08, 12:09 PM
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Does the switch trip and need to be reset? If it doesn't trip it doesn't need to be reset.
Check your intake vent pipe where it attaches to the furnace sometimes the intake will draw in leaves. Should be a screen at the inlet to catch the debris. Also, if it's below freezing in your area you might want to check the intake for where it exits the house for frost. Check for sags in the vent pipe as this will trap water and cause problems.
 
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Old 12-23-08, 03:17 PM
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Venting is ok

I am beginning to think the issue is with a relay on the control board. I currently have it working again. I turned the thermostat off, switched off power to the transformer, removed all the thermostat wires to the control board for about 45 min's. I then reconnected everything and powered up the transformer, leaving the thermostat off. Did a self test and it completed normally.

When I turned the thermostat on, it tried to start. The inducer motor came on then shut off before the igniter began to glow. When it shut down, there was a noise coming from the control board (relay?). At that point i reset the manual reset limit switch (flame rollout switch) and the noise went away and the furnace began working.

Any thoughts? Am I on the right track?
 
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Old 01-14-09, 10:12 AM
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I am also seeing the 31 error code. When I reset several times, the system will work. When it does not, I have the same symptoms that you do: inducer starts then stops and I hear "chatter" that is probably from a relay contact arcing due to bad contacts. I plan to take the control unit apart, pull the IDR (relay) and see if I can get a new one from Grainger or the local furnace shop. I will probably replace the HSIR and BLWR at the same time if they are all the same part (expected).
 
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Old 01-14-09, 10:48 AM
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Well rocket--

I recommend against picking these boards apart. They aren't designed to be repaired. Furthermore, by replacing the circuit board you replace many other parts and thus renew the reliability of the equipment for the future.
 
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Old 01-14-09, 05:10 PM
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Agreed. I will see if I can clean the relay contacts for short term usability while I order a replacement control board. I have been in PCB design for 20+ yrs and indeed, these are not built for rework, just replacement.
 
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Old 01-14-09, 09:25 PM
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Originally Posted by rktscientist View Post
Agreed. I will see if I can clean the relay contacts for short term usability while I order a replacement control board. I have been in PCB design for 20+ yrs and indeed, these are not built for rework, just replacement.


Since you are an Xpert on circuit boards, perhaps you can explain why certain boards may not be repairable.

A LOT of parts used to be repairable, but few are anymore. I've always presumed that a large part of the reason was the liability manufacturers might have if repairs were botched, plus the fact that hey! they simplify the number of products they sell and make more money by selling the whole product rather than just a repair.

And as I said in my earlier post, by replacing the module you are replacing many or all the old parts on many circuits, increasing liability long term.

And of course, since factory repair parts aren't available, people may not pick out parts with suitable specifications, which may cause a variety of other problems.

But if you can explain other reasons why doing this isn't smart, I'd be glad to hear them. Unfortunately, all too often when I help people identify a defect, they are hot to tear into the board despite my efforts to discourage that.

That makes me wince, because I can just see myself being named in the lawsuit after someone kills or injures themselves or someone else.

Frankly, I'm probably a fool for helping people on a board like this.
 
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