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Old 01-21-2010, 07:52 PM   #16
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American Standard Furnace Mystery


I have seen this a few times where the pressure switch was at the open/close point and was rapidly switching back and forth causing the gas valve to chatter. May want to check the venting and drains if it is a condensing furnace.

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Old 01-21-2010, 07:59 PM   #17
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American Standard Furnace Mystery


Does the furnace have its own circuit and a good ground?
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Old 01-22-2010, 06:54 AM   #18
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American Standard Furnace Mystery


I believe that John may be on to something. It is a condensing downflow furnace with a circuit/ground. I have checked all of the vents and they are good. I have checked all of the drains, except the one that exits at the bottom of the unit (where the A coil is located). I'm starting to suspect that perhaps there is blockage somewhere between the header box and that drain exit point. And of course, it would have to be the one that is the most inaccessible. Such is life . . . Thanks for the ideas. I'll be checking them out this weekend.
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Old 01-26-2010, 07:10 PM   #19
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American Standard Furnace Mystery


Well, I have still yet to figure out a solution, but I have found one thing that I can do that immediately stops the flickering from happening. My furnace has two drains internally, one from the header/collector box and another from the inducer. Both drain into a small plastic trap that feeds into PVC down into a floor drain. If I remove the inducer tubing from the trap and just have it drain into a cup, the symptoms completely disappear. I have tried cleaning out the trap using a bleach mixture, but when I prime it and hook the tubing back up, the same symptoms appear. I feel like I'm slowly narrowing it down, though I don't know if this would point to drainage, inducer, or pressure switch problems. Any thoughts on this fix?

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Old 01-26-2010, 07:22 PM   #20
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American Standard Furnace Mystery


Post some closeup pics of the inducer, trap etc and drain from the furnace etc.
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Old 01-26-2010, 07:56 PM   #21
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American Standard Furnace Mystery


You say this has only happened the last few months. Was anything changed, installed, added or removed to the system. Normaly but not always the only way the header drain wont drain is if the trap is empty or if you have a double trap problem. Does the pvc drain dip up and down anywere creating a additional water trap?
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Old 01-26-2010, 08:04 PM   #22
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American Standard Furnace Mystery


Well, I do recall this happening a few times the last heating season, but not nearly as much as this one. No major changes since then. Here are some pics:

http://i14.photobucket.com/albums/a3...e/DSCF3440.jpg

http://i14.photobucket.com/albums/a3...e/DSCF3441.jpg

http://i14.photobucket.com/albums/a3...e/DSCF3442.jpg

http://i14.photobucket.com/albums/a3...e/DSCF3443.jpg

http://i14.photobucket.com/albums/a3...e/DSCF3444.jpg
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Old 01-26-2010, 09:46 PM   #23
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American Standard Furnace Mystery


I may know your problem. Where the drain drops down to the floor it shoud have an open tee instead of an elbow. We install all our furnaces that way. It will allow the pipe to siphon better AND the trap to siphon better and vent itself. We do that to A/C coils also. Sounds like when you remove the inducer drain hose it is doing that function for you.
http://www.diychatroom.com/attachmen...drain-copy.jpg
should look like this.
Don't ask me how it ran like that until now, just try what I said. My method is the industry standard and necessary for all Lennox units and AireFlos.

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Old 01-28-2010, 05:07 AM   #24
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Yuri, that sounds like a good idea. It also led me to discovering what I think might be the problem. The 2' of PVC that runs from the trap to the elbow appears to have developed a slight slant that runs toward the trap. I measured it, and it indeed does have a 1/2" pitch sloping toward the left. This very well may be the problem. I also suspect that over the years, the PVC being so close to the burners caused it to slowly sag. Anyone ever heard of such a case? I'm going to attach some vinyl tubing to the trap and run it into the floor drain just to rule out the trap as the problem. If that works, I may first try to drill a small hole in the elbow, and if that doesn't fix it, I am going to replace the entire horizontal run and install an open tee where the elbow currently is. I also wonder if perhaps I need to reconfigure it to exit out of the left side of the furnace, or else the PVC warping will happen again. Any ideas? I finally feel like I've identified the issue and am going to be able to fix it. Thanks for all the help. I'll update to let you know how it goes.

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Old 01-28-2010, 06:57 PM   #25
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American Standard Furnace Mystery


Probably/possibly the inside of that horizontal pipe is coated in scuzz/algae from not draining properly and slowing everything down causing poor siphoning. Takes VERY little to aggravate the proper operation of the trap. I would replace the pipe and put the tee in. The heat from the burners is NOT good for it but I would wrap it in foil backed insulation rather than add 2 restrictive elbows and go out the left side.

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Old 01-28-2010, 07:12 PM   #26
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American Standard Furnace Mystery


Well, I'm once again not sure what the issue is. I took off the tube from the trap to the drain to see if it would operate correctly. It didn't. Same symptoms. I tried hooking up some vinyl tubing and running it directly to the floor drain. Same symptoms. It appears that the water is being forced to remain up in the collector box and inducer housing. If I unhook either from the top of the trap while the furnace is running, the water flow starts, and I can re-hook it to the trap and everything drains well for the rest of the cycle. Once a new cycle begins, the same vacuum-type conditions seem to happen. Not sure if it's the trap itself or something further up the line.
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Old 01-28-2010, 07:20 PM   #27
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American Standard Furnace Mystery


You may have to remove the inducer fan and check if it has a plastic orifice which attaches to it or the collector box. On the ICPs they deteriorate/break and cause problems. Not sure if the back of that collector box has baffles. The Lennox do. I would remove it and check for slime/scuz there also. You might be able to reinstall it with red RTV silicone if you are careful and let it cure for several hours. I don't see many Trane/AmStd so don't know if you need a factory gasket for it, hopefully one of our guys does.

Last edited by yuri; 01-28-2010 at 07:22 PM.
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Old 01-28-2010, 07:33 PM   #28
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American Standard Furnace Mystery


It does indeed have a plastic orifice. In fact, I did notice that when I removed the inducer, there seemed to be the remains of some sort of grayish caulking, but most of it was gone. Perhaps this could be it. Could the lack of a seal in this compartment cause this issue? Sounds like the perfect setup for the vacuum condition I'm seeing.
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Old 01-28-2010, 07:57 PM   #29
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Sounds suspicious to me. Unfortunately I do mostly Lennox and Carriers and ICPs. Hang in there, must be a few Trane/AmStd techs here, may take a day or 2.
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Old 01-29-2010, 03:23 PM   #30
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I pulled off the inducer housing again and took a look at that gasket again. It turns out that it wasn't caulk that came off. The rubber on the gasket itself appears to have melted. The entire outside/back of it melted off. The front face that sits directly against the face of the inducer has two or three cracks in it as well. I only found the part online in one spot only. http://bestbuyheatingandaircondition...tegory_Code=CP It is apparently obsolete, but I can't find the newer part. Any ideas?

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