# American Standard Furnace Mystery



## David6 (Jan 17, 2010)

I have a 5 year old American Standard furnace model # CDC120A960A3 that has been giving me fits for the past few months. The furnace will sometimes start up normally, and burn without any problems for an entire day. Some days, during a cycle, all of the burners will have a flickering to them, as if the control board is killing the gas, though the flicker is only a fraction of a second and the flame remains lit. The flickering itself is random in its pattern. Sometimes it will flicker once during a cycle. Sometimes it will flicker over and over back to back to where the furnace shuts down the flame and completely restarts. The board LED does not give any error readouts. It continues blinking, indicating regular call for heat. I have had an American Standard tech out to check it out, and of course, the furnace wouldn't do it the entire 30 mins he had it on. On the work order sheet, he says that he checked gas pressure, inducer motor, flue outlet for freeze-up, heat exchanger, condensate drains, blower, ignitor, and flame sensor. He indicated that the valve pressure crept down a bit during the test time, but that it was within normal operational boundaries. I am at a complete loss as to what the problem may be, and if I need to call another tech out, I would like to have maybe narrowed the problem a bit. Sorry for the long post, but this is the first time I have every asked for help via a forum.


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## beenthere (Oct 11, 2008)

Natural gas, or LP?


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## David6 (Jan 17, 2010)

Natural gas


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## beenthere (Oct 11, 2008)

Almost sounds like moisture in the gas. Or a moving restriction in the gas valve or manifold.
Along with possible loose wire connection on the board or gas valve.


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## Yoyizit (Jul 11, 2008)

*24 vac power dropout indicator*



David6 said:


> Some days, during a cycle, all of the burners will have a flickering to them, as if the control board is killing the gas, though the flicker is only a fraction of a second and the flame remains lit. The flickering itself is random in its pattern. Sometimes it will flicker once during a cycle. Sometimes it will flicker over and over back to back to where the furnace shuts down the flame and completely restarts. The board LED does not give any error readouts.


If I post a schematic can you wire up a DPDT relay to do the function in the title? Parts cost would be a few bucks.

You'd hook it up to the gas valve and if the symptom shows it would sound an alarm if the gas valve voltage wavered. If the power comes back the alarm continues to sound. 

If the gas valve voltage stayed constant through the symptom you hook it up to other points that are supposed to have 24v on them until you find a point that drops out when the symptom is present.

If you build two, you could find the problem twice as fast.

It would be good, though, if you can somehow induce the problem. If you can do that, all you need is several LEDs that monitor critical voltages. Even less bucks for parts. 
That's how I found an intermittent cranking problem in my car.


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## David6 (Jan 17, 2010)

Sure, it's worth a shot, but as to getting it to produce the symptoms, it seems to be somewhat random, though I feel that it seems to do it the most in the morning when bringing it from the overnight temp to daily temp. It happened a few times this morning, but yesterday, not at all. Thanks for the input/help.


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## Yoyizit (Jul 11, 2008)

*from Hosfelt electronics, a DPDT relay*

Part number 45-640

Mfg. - GUARDIAN
Mfg.# - 1390VS-2C-24A
1-1/16" x 13/16" x 1-3/8"
13 amp @ 30 VDC/120 VAC
Coil resistance: 160 ohm, 24 vac, less than 3.6 VA

It's $1.75 but shipping is extra.

You need to remove the plastic relay case or find a similar relay with no case on it.

Using only one section [SPST] from the two sections, 
run a wire from the normally open [NO] contact to one coil terminal.
The 24vac goes into the common terminal of that section and the other 24 vac lead goes into the other coil terminal. 
This relay may want a socket, so it may not like soldering temps. You can use push-on connectors or just wrap the wire around the terminals several times. If you do solder the terminals, be quick.

You'll probably need clip leads; Hosfelt may have them.

To latch it to the "armed" position, with 24vac applied and using a toothpick, push the relay armature down until the normally open contact is passing current to the coil.
Now, when power drops out, the armature will release and stay released, so you will know what voltage dropped out.


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## yuri (Nov 29, 2008)

If the pressure is flickering/pulsating there is a VERY good possibility the gas co regulator AND or meter is mechanically failing. I had one where it took me 2 trips and a few dozen cycles of the unit B4 the problem showed up. Kept losing gas pressure intermittently. Gas co changed the meter and regulator and problem went away. The meter and regulator are mechanical devices, can wear out/fail like anything else. I would NICELY talk to your utility co about it, yell at them and you won't get good results. Show them the report from the tech, they are responsible to supply you the proper pressure and amount of gas. Make sure the meter and regulator are not covered in snow or ice and that the screen on the regulator is not covered in spider webs/debris or snow.


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## NHMaster (Dec 21, 2009)

Yes, have the regulator checked.


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## David6 (Jan 17, 2010)

Thanks for the suggestions. I had the luck to actually capture the failure happening on video. If you're curious to see it, I uploaded it online http://www.megaupload.com/?d=LKFQLEOA Around 6:45 is when the complete flicker/shutdown happens. I had another friend in the HVAC field take a look at the video, and he thinks the issue is most likely the control board, as the circulation motor immediately tries to start-up again after the flames go out. The circulation motor runs for around 5 seconds after the flame goes out during a normal cycle, and he feels that something is killing the motor, probably only for a fraction of a second, causing the flames to flicker/shut off as a safety. Any opinions? There is a bit of browning on the control board around some resistors near the top of the board, but nothing I would really call a burn. I would love to hear your guys' take on this theory.


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## David6 (Jan 17, 2010)

Well, I was able to rule out the control board. Another guy I know happened to have a board that I could switch out to test. The symptoms showed up immediately. I'm going to give the gas company a call today and see what they say.


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## David6 (Jan 17, 2010)

Update: Gas company said I was being shorted under full load, so they changed the meter and regulator. Now we wait and see . . .


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## yuri (Nov 29, 2008)

INTERESTING, :detective:
Thanks for the follow up, lots of posters don't.


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## David6 (Jan 17, 2010)

Well, unfortunately, that doesn't appear to have been the problem. Still getting the flickering, with the occasional restart. May have to go the electrical route suggested by a previous poster.


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## JohnH1 (Jan 9, 2009)

I am going to say it may not be the gas pressure. In the video every time the burners shut down I see a large amount of water gushing down the clear drain hose on the left of the furnace. the pressure switch hose is also connected near the same hight as the drain. I belive the water is not draining properly durring operation and flooding enough to quickly block the pressure switch shutting down the burners. The induser shuts down the water drains and starts over again. But then again it is hard to determon with out being there.


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## SKIP4661 (Dec 3, 2008)

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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## qbert (Mar 23, 2009)

Does the furnace have its own circuit and a good ground?


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## David6 (Jan 17, 2010)

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 . . . :no: Thanks for the ideas. I'll be checking them out this weekend.


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## David6 (Jan 17, 2010)

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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## yuri (Nov 29, 2008)

Post some closeup pics of the inducer, trap etc and drain from the furnace etc.


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## JohnH1 (Jan 9, 2009)

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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## David6 (Jan 17, 2010)

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/a317/DavidandDenise/Furnace/DSCF3440.jpg

http://i14.photobucket.com/albums/a317/DavidandDenise/Furnace/DSCF3441.jpg

http://i14.photobucket.com/albums/a317/DavidandDenise/Furnace/DSCF3442.jpg

http://i14.photobucket.com/albums/a317/DavidandDenise/Furnace/DSCF3443.jpg

http://i14.photobucket.com/albums/a317/DavidandDenise/Furnace/DSCF3444.jpg


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## yuri (Nov 29, 2008)

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/attachments/f17/6768d1230426592-furnace-drain-problem-g51-drain-copy.jpg
should look like this.
Don't ask me how it ran like that until now, just try what I said. :thumbsup: My method is the industry standard and necessary for all Lennox units and AireFlos.


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## David6 (Jan 17, 2010)

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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## yuri (Nov 29, 2008)

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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## David6 (Jan 17, 2010)

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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## yuri (Nov 29, 2008)

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.


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## David6 (Jan 17, 2010)

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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## yuri (Nov 29, 2008)

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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## David6 (Jan 17, 2010)

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://bestbuyheatingandairconditio...en=PROD&Product_Code=PVC8400&Category_Code=CP It is apparently obsolete, but I can't find the newer part. Any ideas?


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## David6 (Jan 17, 2010)

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. 21D340234 P01 http://bestbuyheatingandairconditio...en=PROD&Product_Code=PVC8400&Category_Code=CP It is apparently obsolete, but I can't find the newer part. Any ideas?

I think I found the bulletin that was sent out for this very issue. Those parts pictured are identical to the ones in mine only flipped since mine was converted to downflow.

http://docs.google.com/viewer?a=v&q...&gl=us&sig=AHIEtbTMmVrjaiU3Pgp2Wx9tfwBVgmMLvg


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## JohnH1 (Jan 9, 2009)

That bulletin does not describe your problem. Eather you are drawing to much negitave psi overcomming the hight of the trap. or mabye the trap is not trapping the water.
Look into the trap to see the wall in the trap still in place inside the trap assembly. Without a trap you will suck air up the drain tube and not allow condensate out of the furnace untill the suction stops (IE: induser stops) this is what it looks like. I have never seen a trap fall apart but anything can happen.

John


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## yuri (Nov 29, 2008)

It could happen as they are only held together with a thin layer of silicone or it was built on a Friday afternoon or Monday morning.:yes:
John, I am surprised that trap is not vented with a 1/4" hose like the Ducanes/AirFlos and Carrier and ICP traps. Poor design IMO.
Back to the Deep Freeze here, will try send some of it South, LOL:laughing:


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## JohnH1 (Jan 9, 2009)

yuri said:


> It could happen as they are only held together with a thin layer of silicone or it was built on a Friday afternoon or Monday morning.:yes:
> John, I am surprised that trap is not vented with a 1/4" hose like the Ducanes/AirFlos and Carrier and ICP traps. Poor design IMO.
> Back to the Deep Freeze here, will try send some of it South, LOL:laughing:


I will take the cold it is good for biz. I could always use more work.:thumbup:


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## David6 (Jan 17, 2010)

I found a forum on another site where the pictures are exactly what mine looks like.


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## beenthere (Oct 11, 2008)

Please don't post links to a competing forum.

Maybe you want to down load the pic. And then upload the pic to here.


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## David6 (Jan 17, 2010)

beenthere said:


> Please don't post links to a competing forum.
> 
> Maybe you want to down load the pic. And then upload the pic to here.


Sorry, thank you for the correction. I should have thought before doing that.

Upon reading the bulletin a few more times, John is right. Luckily, I don't see any signs of a cracked collector box. I'm keeping my fingers crossed. I think my problem is just the transition. I've tried to track it down online (#RCT00084), but I'm having no luck. The Trane parts store near me is closed this weekend. Any idea how much I'm in for? I just want to be prepared for sticker shock.  Thanks all, I think I'm close.


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## beenthere (Oct 11, 2008)

No, I have no idea.


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