Carrier 48SS locks out with "internal control fault" when cold outside

I have a Carrier 48SS-036100331-- (about 11 years old) and my house is approx 1750sq ft. The heat works fine when the outside temp. isn't too cold (ex. greater than 50 degreesF). However, when it is colder outside, the unit frequently locks out. The exhaust fan continues to run, but the burner isn't lit. I had to have my heat exchanger replaced last season. I vaguely remember the technician saying it was likely there wasn't enough airflow, so the exchanger was getting too hot which decreased it's lifespan. This made me suspect that the limit switch was tripping. However, the led on the controller board blinks 8 times when it's locked out, which corresponds to "internal control fault" according to the schematic. I have opened all my dampers to maximize airflow. When I flip the breaker off then on again to the unit, the burner will light up again and will work for awhile and then lockout again if it is cold outside. Here are pictures:
http://www.commercialinstallations.com/Misc/heat.htm
Any ideas? "Internal control fault" sounds like the controller board, but why would it work except when it gets cold out? What is the best way to troubleshoot "internal control fault" error?
Thanks, Casey
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look in the middle of the circuit board, see the two big square white resistors and the two resistors immediately above them? One looks like its been over heating....also the mounting holes/slots in the ignitor assembly.....sand paper the metal around those mounting locations as well as their corresponding mating surfaces where they mount. you need a good grounding connection there...
too bad when they replaced your heat exchanger they didnt also replace the totall rusted out inducer housing. Inside that inducer housing is a totally rusted inducer blower wheel. the wheel should have been replaced as well, as they tend to disentegrate
also, check for tightness on all stake on connectors and the edge connector on the ckt board. those units are notorious for over-firing. be sure to check and set the pressure at the gas valve. your service tech should have de-rated the burners if its overfiring
see that round black gizmo with wires coming out of it at the back of the inducer motor? thats the Hall-Effect sensor, a total piece of shit. It tells the control board the inducer motor is running and its ok to open the gas valve and spark the ignitor. It is a piss-poor design though, as the inducer motor can be spinning a totally rusted out inducer wheel. So when the gas ignites, you get major flame roll-out, which usually burns all the wiring up. Did I mention I LOVE CARRIER??
finally, take a shop vac to the crap in the bottom of the burner compartment. cleanliness is next to godliness.
ps- error code 8 is carrier's way of saying.....get ready to spend the big bucks....
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On Sun, 21 Jan 2007 00:34:01 GMT, snipped-for-privacy@gonefishin.net wrote:

Shhhhhh. Cmon Fish........dont give away all the secrets. We just luvvvvvvvv those Carriers. Its the best equipment on the planet <snicker, snicker> Well, they have to be right? All their commercials say so. :-) Who else can go through about 10 revisions of a shitty circuit board and keep charging the customer for it? Carrier......Thats who. We love you. Just like money in the bank Bubba
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Thanks for the reply.
Yeah, those two resistors do look like they have been overheated.
I cleaned the ignitor and flame sensor and where they contact the mount yesterday (with steel wool and wire brush). I thought that might have done the trick because the heat worked all day yesterday afterwards and this morning (which was very rare beforehand). However, it was locked out when I got home today. :(

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wrote:

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LOL!! You're cruel!
--
Respectfully, Bob

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Soap and water (while powered up of course) was sufficient. Not only is the controller board heating up and glowing red, but it also plays music now.
Seriously, I plan to check all the connections to make sure they are secure and everything, that should be, is well grounded. If that doesn't fix, I have to assume the circuit board needs to be replaced.
wrote:

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responding to http://www.homeownershub.com/hvac/Carrier-48SS-locks-out-with-internal-control-fault-when-co-11733-.htm mark356 wrote: ??? Leave it powered up and scrub the back of the circuit board with oo steel wool to get the soldered connections clean???
Is this a joke? I don't know much about heating and cooling but I'm an EE and this is not a good idea for any circuit board. It will short out components and most likely damage the board. If there is high voltage on the board it could burn or electrocute a person. It would also not fix any bad connections on the back of the board.
This has to be a joke for people who know better but some non-technically inclined person may actually try this. Not very funny.
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On Sat, 11 Dec 2010 15:28:43 +0000, mfiedler356_at_gmail_dot snipped-for-privacy@foo.com (mark356) wrote:

    Which explains why you didn't get the joke.
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Click here every day to feed an animal that needs you today !!!
www.theanimalrescuesite.com/
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guard0g had written this in response to http://www.thestuccocompany.com/hvac/Carrier-48SS-locks-out-with-internal-control-fault-when-co-11733-.htm :
I had a similar problem (as have many others) and hope this information helps. --John
Symptom:
Intermittent furnace lockout with Internal Control Fault (8 flashes), sometimes accompanied by the "modified fan blower delay" fault (1 flash). Problem occurs especially when the temperature falls below 32 degrees. Exhaust Fan continues to blow after lockout. Checked rollout switches and flame sensors, no problem.
Cause:
Excessive vibration triggering the relays on the Integrated Control Panel, which cause the internal control fault (usually the vibration can be felt by touch on any part of the unit)
Temporary Fix:
Dampen the vibration to the control panel using high-temp flame-resistant padding.
Permanent Fix:
Vibration most likely due to imbalanced exhaust blower wheel (cage wheel inside the blower that pushes flame exhaust out of the unit). Replace blower cage wheel.
Casey wrote:

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