goodman furnace issue

[mattmctree]

Last winter I noticed that my condensate from my furnace was black and sooty. Upon opening I found the gas to be pulsating on low fire and not high fire. The pressures for low and high were also set for the same pressures. I replaced the gas valve and orifices( I'm on propane). The pulsing went away. I used a comustion analyzer and was getting close to 400 ppm. I called goodman tech support and they said 400 ppm was normal and that the pulsating gas would have cause the sooting. I was cutting the grass the other day and noticed all the grass dead by the exhaust. The furnace is not that old. How do I go about inspecting and cleaning the primary and secondary heat exchangers as I want to make sure it's safe. Sounds like a dumb question however I'm still green at combustion trouble shooting.

[Admin]

You can download the Carrier Service Bulletin 09-0022 - Here

The same steps would apply to a Goodman furnace.

[mattmctree]

Has anyone had any similar issues with goodman furnaces? What typical combustion readings are to be expected on a high efficiency furnace

[walker]

most Goodman I see around 80-120ppm before doing a manifold pressure adjustment,  after adjustment I typically get them down to around 15-30ppm

[mattmctree]

Thanks walker. I adjusted my pressures to what was listed in the conversion kit. I set them at the higher end of the range. Seeing as you have worked on Goodman do you have any experience with swapping our the heat exchanger.  I'm assuming that it comes as a primary and secondary assembly.  Are they easy to change out or would I be better off getting a new furnace. I'm going to try and inspect the heat exchanger. The service bulletin says not to use a smoke bomb so I will have to try and get a camera in there. Is there any recommended way to test for a cracked us.

[walker]

there are some Goodman/Amana units that have a bad seal where there primary meets the secondary.  There's a service bulletin out on it that I don't have at the moment, you could have one of those units and there should be a warranty on it.  Visually finding a crack is the easiest way,  I don't seem to ever many goodman heat exchangers with cracks in them,  I mostly just see them leaking at the secondary.  They're pretty simple to replace from what I remember but I haven't done one in a few years.  Try setting the manifold on the lower end of the range and watch your combustion analyzer, I bet your CO will drop.

[Admin]

Yah, I've seen that problem before.  Cut an inspection hole in the plenum above the back of the furnace and look down inside the furnace for an orange gasket that looks like it's out of place.

[mattmctree]

Perfect once my analyzer get back from repair I will do that. Has anyone had experience cleaning out a secondary heat exchanger or at they pretty much shot when sooted. Just trying to get my ducks in a row for what I find

[mattmctree]

I contacted goodman and they gave me a heat exchanger under warranty . I'm going to pull the old one at some point soon and install the new one. The installer only single piped the unit so I am going to dual pipe it as well. Never done a heat exchanger before on a furnace so I'm hoping that it will go smoothly and that the high co issues will be solved

[walker]

I found one of those goodman furnaces in question the other day.  Here's a picture of what can happen.

[mattmctree]

What is the orange stuff on the secondary exchanger.  I will take some pics of the one I pulled out. It was sooted up quite badly. I checked my pressure and my supply is 10.7 . Low is 6 and hi is 10. Not sure why is was shooting up so bad as the pressures are on par with manufacturers specs

[walker]

What is the orange stuff on the secondary exchanger.  I will take some pics of the one I pulled out. It was sooted up quite badly. I checked my pressure and my supply is 10.7 . Low is 6 and hi is 10. Not sure why is was shooting up so bad as the pressures are on par with manufacturers specs

That is the gasket between the primary and secondary header

[mattmctree]

Haven't been home in a while and with this heat wave haven't been needing the furnace. The heat exchanger was surprisingly easy to change. All one assembly that slides in. My gas pressure are pretty much bang on. The old one was sooted very badly took almost 2 cups of soot and white powder out of the old one but found no cracks. This weekend I am going to do a temp rise test. It says on name plate 30-60 so I'm assuming the difference between supply and return air should be in around the middle at 40. I'm also going to put some drive clear under the rear of the furnace to give more slope for drainage. Other than getting the pressures and temp rise correct I can't think of what would cause it to soot up like it did. The gas valve as I previously stated was cutting on and off every few seconds which I'm thinking could have caused soot up but due to the amount in the heat exchanger it must have been doing it for a long time.  Everyone I talk to in the field tells me that Goodman are garbage. Any one else have other experiences with them . Pretty new at combustion and proper set up so sorry If I'm long winded

[walker]

That's most likely carbonic acid, its basically dried up condensate.  It usually occurs when a furnace is underfired or has improper venting.  I've also read before that furnaces that don't have enough of a post cycle purge on the ventor can cause build up of this stuff.

[mattmctree]

Hmm I'll read the installation manual but can't see anything wrong with the venting. It's no more than 20 feet and has 4 45 s. How do you adjust post cycle purge or is it fixed

[walker]

Hmm I'll read the installation manual but can't see anything wrong with the venting. It's no more than 20 feet and has 4 45 s. How do you adjust post cycle purge or is it fixed

It's fixed.  The manufacturer / control board determines it.  Was your unit underfired at all?

[mattmctree]

So I set up my furnace over the weekend. I've got 10.8 inches  supply pressure.  I set low to 6 and high to 10 as per conversion instructions and when I took my combustion I was getting on low fire 12 ppm co  10 percent o2 and 87 stack temp. And on high fire 13ppm co  9 percent o2 and 86 stack temp.  The temp rise rating for low and high were 30 -60 degrees f and I am getting 48.5. I think I've got it set as good as I'm gonna get it

[walker]

Numbers look good