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Old 03-29-2013, 04:02 PM   #1
jkv
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I have a gas rooftop package I was thinking of a cracked heat exchanger there is black smoke coming out of the exhaust but no flame role out or discolored flame I have a new control board coming in tues. and will be abe to fire it up to further check this. The control board was strip out of this unit, all I know for now any ideas would be great.

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Old 03-29-2013, 04:44 PM   #2
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Originally Posted by jkv View Post
I have a gas rooftop package I was thinking of a cracked heat exchanger there is black smoke coming out of the exhaust but no flame role out or discolored flame I have a new control board coming in tues. and will be abe to fire it up to further check this. The control board was strip out of this unit, all I know for now any ideas would be great.
I wouldn't think a cracked heat exchanger would cause black smoke. Black smoke is caused by incomplete combustion. IMO a more likely cause would be an improper fuel/air mixture either from gas pressure not being properly set or a partially blocked flue/clogged heat exchanger.

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Old 03-29-2013, 08:05 PM   #3
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you can't tell by the flame color if the combustion is correct, i.e., not making carbon MON oxide or smoke..But, seeing as there is black smoke it is definitely producing CO AND SOOT that will clog up the heat exchanger and make matters worse...it's a vicious cycle if left unchecked..as previously stated, the fuel and air ratios are way out of calibration..BEST to call aPRO who has the experience and equipment to check/clean/reset the combustion as required...If left it can burn out the heat exchanger and the whole unit as well...TURN IT OFF until you can get it serviced properly. NOT a DIY
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Old 03-29-2013, 08:07 PM   #4
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just curious..if the control board has been stripped out then, how is the unit able to run?
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Old 03-30-2013, 07:49 AM   #5
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Shut it down, tear it open, clean it throughly, complete internal inspection, close every thing up, replace all missing controls, startup, calibrate controls, now troubleshoot.
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Last edited by COLDIRON; 03-30-2013 at 07:50 AM. Reason: added text
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Old 03-30-2013, 08:58 AM   #6
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Thanks guys I was fuguing this was the problem I removed the control board to put in the other unit I have four of them on this roof all has problems I have three up and running. Another company claimed the heat exchanger, I did not feel this way, always good to have conformation. Thanks
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Old 03-30-2013, 12:46 PM   #7
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if there is any soot in the air supply ducts OR coming out of them..then..could still be a cracked heat exchanger
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Old 03-31-2013, 09:19 AM   #8
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Originally Posted by COLDIRON View Post
Shut it down, tear it open, clean it throughly, complete internal inspection, close every thing up, replace all missing controls, startup, calibrate controls, now troubleshoot.
There's your answer. If another company condemned the heat exchanger you better be 100% sure that's not the problem before getting it operational. Doesn't take but a pin prick of a hole in the right place to cause incomplete combustion and soot.
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Old 03-31-2013, 11:02 AM   #9
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Make sure what you are seeing is "black soot" and not deteriorating black or dark gray insulation from the inside of the unit. If it is soot it will be greasy and smear easily. I have had many service calls where customers describe "black soot" only to find that it is not. I have seen very few gas fired units so far out of adjustment that they produce soot that bad. Usually there are other symptoms such as roll out switches tripping(even with no flame roll out), high limit switch tripping, temperature rise across exchanger too high. Ultimately a visual inspection is the best way however. You didn't say the age, model or make of the unit.
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Old 03-31-2013, 09:09 PM   #10
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What brand and how old are these units?

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