1996 Carrier Heat Exchanger Cracked?

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Hi All... my neighbor's carbon monoxide alarm goes off, she shuts down her 1996 Carrier Weathermaker 58TUA hi-efficiency furnace, calls in Frank the HVAC guy, and after a peek inside (from the top), Frank concludes that the heat exchanger is cracked and a whole new furnace is needed.
Is this possible? Common? How can you tell if it's cracked (it looks like new haha)? What else might be the matter? Carrier had a 20yr warranty on those things back then... shouldn't a suggestion be made to use it? This was an expensive furnace... wt*?
Thanks for all of your help, :Dan
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did he actually *SHOW* her the cracks??

Yes its possible, especially if it wasn't installed and set up correctly. Was it serviced every year like its supposed to?? You wouldn't buy a new car and try and run it for 12 years without ever having it serviced, would you?? Why would you do it with the single most expensive appliance in your home??

The tech should have *SHOWN* the home owner the cracks

Its broken... there are several reasons it could have set off the CO detector... cracked HX is a likely culprit, as well as over-firing, partially blocked vent pipe, etc.

Replacing the HX will cost almost as much as a new furnace...even if Carrier warrantys the HX.

Expensive is relative... If it was the cheapest price, then all bets are off. If it wasn't installed by a *competent*, licensed, insured, professionaly trained, Master HVAC Tech, then all bets are off.

Your welcome

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the cost of the CO detector turned out to be a good investment.. Mark
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On Fri, 17 Oct 2008 03:22:18 -0700 (PDT), dantheman

Possible? Yes. Common? Define common. It happens......yes.

The tech saw the crack so the tech should be happy to show the homeowner the crack.

The furnace could be in need of repair or the carbon monoxide detector is detecting something else or is defective.

Sure but it'll be about as much as a new furnace and thats if the heat exchanger is still available.

Define expensive.

In a nut shell a 2nd or 3rd opinion might well be worth the call. Bubba
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It's just the normal shit that Frank pulls on a daily basis. Now tell your friend to call someone that's competent this time!
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kjpro @ news .com wrote:

You should [listen to kjpro]. Get a second opinion. Find a service company with a "Gas Analyzer" to check for CO coming from the appliance. They can also check for a crack by checking the CO level before, during, and after the furnace is in operation in the flu. Your local utility may offer a free inspection to confirm the HVAC service tech's opinion.
--
Zyp



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Zyp, Just a slight correction. A CO detector will NOT always find a crack in a heat exchanger. Many furnaces with cracks support proper combustion just fine. I wouldnt want that furnace in my home but a crack in a heat exchanger doesnt always burn "dirty" and cause carbon monoxide. Im just restating that but Im sure thats what you meant. :-) Bubba

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You know the HX is cracked when the furnace cycles off and the pilot gets blown out by the fan, or it trips the roll-out switch(s)
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Steve wrote:

Not necessarily so. The ventor fan sucks ad does not blow.. And the crack is usually on the top side out of the airstream of the indoor blower. An infrared camera can spot it when still hot. Or sometimes smoking it right after shut down There are many furnaces that are diagnosed with cracked exchangers when all that is wrong is a clogged chamber in the seconfdary exchanger. This most oftern occurs on propane furnaces and is due to improper firing. This can be crappy tuning or a wide variance in the BTUH of the fuelgases. In the winter moisture is either added or condensed into the gase to make it easier to shove up the pipelines. This moisture is what causes a tarring effect in the chambers when the mix is bad.

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The furnaces in this neck of the woods are all 80%(or less on the old ones) They don't have a secondary HX.
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My example is a 80% unit...
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Noon-Air wrote:

Most here are updated to the high efficiency ones. I guess I thought you folks would be more into Heat pumps. As for your take on 80% furnaces.. I concede.. That is the main way of diagnosing cracked exchangers.

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wrote:

Im just sayin.....I had a Tempstar a few years back (90%er) that I got a call on no heat. It was the main limit (the little camstat POS) that failed open. I finally looked in and the plastic collector on the side of the secondary had a hole in the top of it big enough to put a tennis ball in. The burner roll out never did trip. His CO detectors never went off (most of them wont though but thats a whole nother story). Ive had many Tempstars and Janitrols that I found popped rings on that were burning just fine. Its a bit harder to condem someone's furnace when they call for a "tune-up" and you have to give them the "good" news about their working defective furnace. Bubba
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All the furnaces in this neck of the woods are 80%ers, or standing pilot.
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Yep, most will continue to use them till they DO trip the rollouts. <rolleyes>
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Not exactly true... Tripped rollouts on a unit with no vent pressure switch. Problem? (it had a perfect heat exchanger)
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It's a 12 yr old Carrier... They had more than their fair share of lousy heat exchangers... I'd look into that 20yr warranty, although being prorated...
geothermaljones

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Nope, Lennox and the heat exchanger is fine...
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kjpro @ news .com wrote:

Using a CO gas analyzer can measure the CO from the flu. Generally something less than 18 ppm for most gas fired furnaces. When the indoor blower comes on and forces positive pressure into the heat exchanger [a rupture] will in most cases show the CO going down. [An increase in unburned gases [air] getting into the firebox will show a decrease in CO because of dilution.] When you see this condition, it warrants pulling to blower and / or burners for further investigation.
The Carrier of a 1996 vintage will have an aluminized heat exchanger, albeit it's installed correctly would have a good life span, but if there's insufficient air... well you know. :)
--
Zyp



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Ok, here's a clue for everyone... What problem can exist from a unit with no pressure switch (and no other fault sensed), yet it trips the rollout?
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