Trane XE 80 / XE80 ignites and burns but still blows cold air

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  #1  
Old 10-17-10, 06:43 PM
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Trane XE 80 / XE80 ignites and burns but still blows cold air

My wife turned on the heat the other day and told me it was blowing cold air so I started looking into it...

everything with me is very similar to this thread:

http://forum.doityourself.com/gas-oi...imal-heat.html

System: Trane XE 80
Model: TXC025C4HPB1
Mnfd: 01/98
Ignitor: Norton 271N

Everything seems to work just fine, just like the thread above step for step until: after the ignitor heats and the gas fires and then just about as soon as the ignitor cools "completely" there is 1-3 clicks and the flames go out. then I get a 3 flash error code.

The process repeats itself with the ignitor, fire/flame, ignitor cooling, 1-3 clicks and blackout. It eventually goes to 2 flash lockout after 3-5 repeats.

inside the lower panel it says 3 flashes is a pressure switch problem.

1. Is the pressure switch the round "car-horn" looking deal with the white/clear tube on the back of it?
2. Which wires do I bypass to see if the pressure switch is the issue?
3. Are there any other systems to check, resistance, voltage, etc?
4. I haven't checked the exhaust duct 3" that goes into the chimney since I just don't see varmin coming 25-30 feet down to plug up a new home...but it's certainly possible.
5. I haven't taken off the white/clear line to give the switch my own amount of vacuum since I'm not yet absolutely positive that's my pressure switch

I also got a couple times...
~30 seconds from flame to black out
~35 seconds to repeat

then I came upstairs and turned off the t-stat and started this. I can take some pics later if necessary. thanks for reading and I hope I can learn from this and help others

best regards,

Chris
 
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Old 10-18-10, 07:03 PM
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Remove and clean the flame sensor probe, located in the burner, on the opposite side from the HSI heat coil ignitor. Usually only one screw holds it in place. Has one skinny wire coming from it, that leads back to the controlboard or module. Turn off furnace, remove rod, and polish it with steel wool or scotchbrite pad, to get rid of a film on it that prevents the probe from sending a small current signal back to the control module or board.
 
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Old 10-23-10, 06:09 AM
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so I finally got a chance to take care of this and it didn't fix it. It is still flashing three times.

I also pulled off the white hose and gave it some suction and it seems like the suction part of the switch works because it pulled that little white stopper back up into the hose BUT that didn't fix anything while running the machine. and I know for a fact that the stopper doesn't move when in place.

so I'm guessing that rules out that switch? What else is there...the flue being stopped up?

I just got called into work, no more fun for me here. thanks in advance for further thoughts and help!

Chris
 
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Old 10-23-10, 11:30 AM
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My suggestion is ---- post what you see and observe. Don't make references to other threads. However much you think your problem id the same, it's not relevent to what your furnace is doing.


And frankly, I'm not interested in hunting through other threads you think might be relevent.

Of course, you can do as you wish. But it means you do without my help, and perhaps that of others.
 
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Old 10-23-10, 12:37 PM
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Originally Posted by walth View Post
so I finally got a chance to take care of this and it didn't fix it. It is still flashing three times.

I also pulled off the white hose and gave it some suction and it seems like the suction part of the switch works because it pulled that little white stopper back up into the hose BUT that didn't fix anything while running the machine. and I know for a fact that the stopper doesn't move when in place.

so I'm guessing that rules out that switch? What else is there...the flue being stopped up?

I just got called into work, no more fun for me here. thanks in advance for further thoughts and help!

Chris
The suction inside the furnace, when the smaller draft inducing fanmotor runs, will pull in the plunger. If it is not doing it then, and only does it by sucking on it, you have something plugged with the furnace, more than likely. It can be something as simple as the nipple, where the hose plugs into the inducer, being plugged. You can clear that out with say the right size drill bit, by hand.

There can be several other causes, like ill-fitting vaccum hose, bad pressure switch diaphram, backed up condensate water in the furnace, clog in intake(if you have that) or exhaust piping, bad inducer motor or detached fanblade, clog or breakage in furnace itself. First, follow the next suggestion.

If the fact is the pressure switch is telling the furnace not to work, for safety reasons, you can voltmeter test the wires/terminals at the pressure switch, to see if one or both terminals are letting current pass, when the inducer motor runs. Let us know, or if you need exacting help.
 
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Old 10-23-10, 12:58 PM
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Posted model number is for the cased evap coil.

Look inside of the furnace for the correct model and post it.
 
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Old 10-23-10, 05:27 PM
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Originally Posted by Jarredsdad View Post
Posted model number is for the cased evap coil.

Look inside of the furnace for the correct model and post it.
sorry about that, and thank you for letting me know, it's the white rogers 50A50-473.

ecman, thanks a mil,

I will say...

---the vacuum line fit fine, straight, clean
---I doubt it's the condensate pipe, don't know if this is working properly, but there is air flow coming from the condensate pipe while the furnace is running.
---(A) Bad pressure switch diaphram, could be...
---(B) Intake/exhaust flue clog, yeah...I'm going to look at this next. Intake wise, idk if I have that. >>>10 minutes later>>> I just took the exhaust apart. it's wide open and I can see the other side of the chimney! BUT I also have a small trail of grit/sandy material about an inch wide all through the duct from the chimney and leading into the downtube of the duct coming from the fan area. I'm sure that's probably somewhat common and hopefully is my issue deeper into the exhaust duct down by the fan and pressure switch.
---*bad inducer motor* I don't know yet...is this the little motor with two fans? one in the exhaust and one to cool the motor? It runs fine (or seems to) and doesn't seem to have any broken blades...
---*clog or breakage in the furnace itself* hope not but haven't diagnosed far enough yet.

(A) If the switch is bad can I jump the connection with clips to see if that's exactly the problem? Secondly, if the diaphram is clogged with that grit, is there a way to take it apart to clean it out? I didn't look at it much but it seems like it's bent over all the way around?
(B) I haven't heard anything resembling this, but could any of that grit slow down the air flow in the base of the exhaust duct? And if so, or if it becomes necessary later, is there an "easier than it looks" way of removing that panel with the "inducer fan / motor combo" etc?

with all of that said, I again greatly appreciate the time and help here! thanks

Chris
 
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Old 10-24-10, 11:46 AM
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Originally Posted by walth View Post
---I doubt it's the condensate pipe, don't know if this is working properly, but there is air flow coming from the condensate pipe while the furnace is running.
How are you detecting the airflow from this? Exactly where is this pipe, in relation to other parts of the furnace, that you refer to? The nipple I speak of (that the pressure switch vacuum tube plugs into) is often right in the iducer fan housing, and you can hardly detect any air flow from it. And that is whan it is working! It is a very, very minute suction. That is why I wonder what part you are refering to.

Did you remove any condensate hoses and try to back-blow through the tube/hose back towards the furnace, also? That could free up possible gook clog at secondary exchanger area.

I can't remember if you have a voltmeter to test to see if the 24 current passes through the pressure switch as that knowledge would allow us to move in the right direction as to maybe a board malfunction or mechanical issue in furnace. You can jumper wires, but what if that makes the furnace run, and you just leave it without fixing the cause of the problem?
 

Last edited by ecman51; 10-24-10 at 12:06 PM.
  #9  
Old 10-24-10, 01:18 PM
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I may be confused about the condensate pipe?? The regular drain that comes out of the furnace they put a T (one up and one down; the up has a non-glued cap to look inside and this is what I was talking about with the airflow. And obviously the one down is the normal drain). It's a pretty strong airflow too, not featherlight airflow like you mention from the fan inducer housing.

I haven't tried blowing back through the tube, that's a great idea. I've got family intown but I'll do that next.

and as far as troubleshooting, I try to always do things right. I'm not interested in bypassing a safety switch for more than a few minutes to see what's going on. In fact, that idea was just because I didn't know it was "24 current" << is that volts? I've got a few multimeters, I'll do that before bypassing anything. and to go along with that, I'll take a few pics once I find my cam.
 
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Old 10-24-10, 01:38 PM
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24 volts ac current. Set voltmeter to ac volts range scale higher than expected current, like 200 range scale.

Do you have about a 1/4 inch vacuum tube that goes between a pressure switch and the housing for the draft inducer? If you do......where it plugs into the housing is a nipple, and down inside there it can get crud that blocks off the needed suction. That suction is tiny enough the way it is, let alone to have any of it blocked. Undrained condensate water in the furnace can also upset that tiny suction also.

If you could post clear, close-up pics of your furnace, that be nice to. Everyone here likes to look at pictures anyway.
 
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Old 10-24-10, 07:25 PM
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interesting about the nipple inside the housing. had no idea; I'll check that tomorrow.

I forgot flickr doesn't allow "embedding pics" anymore, but here's the link to the album and you can scroll through them and if not let me know.

100_6377 | Flickr - Photo Sharing!
 
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Old 11-01-10, 10:06 AM
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well, the last time I was here, I read about blowing back through the white hose into the flue to clear particles, etc. I did that right after getting off the site last week and it may have fixed the issue.

I also, just now, took my shop vac and switched the hose over to be sort of like a leaf blower and blew out all that grit into the chimney. In case of concern, I did NOT take it and blow it down into the furnace half of the flue. lol.

my only other concern...just now while I was multi-testing the pressure switch (which works now, btw...it had to of been the white hose issue) there was NO voltage whatsoever. >>>(5 minutes later) yeah, I just got back from making sure...I checked between the negative and each hot and then I put both probes to each hot themselves and there was nothing. Is this an issue? I don't really understand how that switch works if neither of the hots even have power to them from the getgo...

on the flip-side, thank thank thank you guys. Especially to ecman51`, I sincerely appreciate your time and what so far seems like a world of success with this troubleshoot. thanks again and I'll be around

let me know what you think about the 24vac as it's been a good 20 minutes+ now and still working great! warming up nicely here in the house
 
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Old 11-01-10, 10:43 AM
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Test for voltage between the furnace chassis as ground and whatever wire or connectuion you want to check.


You will typically have voltage at the pressure switch only when the thermostat is calling for heat and when the inducer motor is switched on.

How many wires are there to the pressure switch?
 
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Old 11-01-10, 10:48 AM
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I guess I should have figured the body of the furnace could be a ground as well...

there's three wires. two are "on a two-prong connector" and they're both orange and I assumed hot wires. Then there's a single connector, which I assumed was the negative side to the switch and I don't recall the color.

I'll do my best to check it in the "morning", I'm a little behind getting ready for work so I gotta get movin. these 12-14 hour days are something else.
 
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Old 11-01-10, 12:01 PM
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The pressure switch is a single pole, double throw switch.

One contact is probably labeled C for common. Power goes to that whenever the inducer motor is on.

The NC contact would have 24 VAC to it when the inducer motor is on but hasn't come up to speed.

The NC contact would have 24VAC to it only when the inducer motor has come up to speed and verified that the venting system is working OK. When power appears on that terminal the rest of the ignition cycle commences.
 
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Old 11-01-10, 03:58 PM
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Originally Posted by walth View Post
............... and then I put both probes to each hot themselves and there was nothing. Is this an issue? I don't really understand how that switch works if neither of the hots even have power to them from the getgo...
When you have no power between the two hots, as you call them, that means the pressure switch IS closing correctly, and shows 0 volts because you are testing in series. That is why I am reluctant to suggest people test the pressure switch this way, as it would mystify too many people that if they knew it SHOWED voltage, it's NOT working - and if it DOESN'T show voltage, it IS working. Seemingly backwards results - but they are not. If you did do the series method of testing, then you also must first establish that you even have incoming current to one of those spades on the pressure switch. You can't just presume it all works if you show 0 volts on a series test.

If you test the way SP and I have said, there is no confusion, because the results seem more logical to the DIY-er.
 
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Old 11-05-10, 01:52 AM
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well, today it's gone back to having a pressure switch error again. (I say today...more like yesterday it started doing it again). I immediately went down, pulled the white hose and blew through it and that did nothing.

I feel like that "pressure switch" vacuum switch isn't the issue. It's got current all the time when it's running. And just thinking through some of the explanations of the 24 vac... if it's got current all the time, that means the inducer motor is up to speed / logically working properly? can I rule out both of those with that logic?

I also took some more pics. there are two "sensors / switches" that are inline with the yellow wires on the pressure switch. I have no idea what they are but they have a little button on the back of them. what are these and could they be the issue?

right side: 100_6397 | Flickr - Photo Sharing!

left side: 100_6396 | Flickr - Photo Sharing!

I also took a pic of the texas instruments black box with the two wires (pic link below). I'm positive it has something to do with the internal piping of the heat induction system (which leads to the pressure switch system, correct?) and I'm wondering if there's anything I can clean on the other side of it?

100_6402 | Flickr - Photo Sharing!

I also noticed down in the bottom on the actual fan there's some sort of sensor? I know I'm like picking stuff out and wondering if these are issues...I've heard of people simply cleaning one thing and their system working. I think it's possible I may be that lucky; we'll see. Especially since it was working great for a couple of days but idk what it's up to now. pic of that below as well.

100_6410 | Flickr - Photo Sharing!
 
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Old 11-05-10, 05:11 PM
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If you have power at both pressure switch terminals, you are right, you do not have a drafting or pressure switch issue.

The inline yellow wires that go to these other safety circuit devices that have push buttons, more like push pins - if you can push them in, and you hear a click, you reset that.

Have not looked at pics yet. I'm going nuts responding to all the posts on furnaces tonight. Wish there was more help. Fish fry/movie night, I guess.
 
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Old 11-05-10, 07:18 PM
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yeah, this is the time of the year for heat issues, lol.

those safety switches go in/out about 1/16" to 1/32" and don't stay put nor do they click.

enjoy the fish fry and movie! I can't say thank you enough for your time.
 
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Old 11-06-10, 10:44 AM
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If the little reset pins just sort of wiggle about when pushed, and no click, then they are not tripped.

How did you test to confirm you have 24 volts traveling thru the pressure switch, exactly?
 
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Old 11-06-10, 06:12 PM
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I haven't been able to get that reading...

so far my methods have been 1*:
Originally Posted by SeattlePioneer View Post
Test for voltage between the furnace chassis as ground and whatever wire or connection you want to check.
and 2*: @ the pressure switch itself, with the negative and positive inline on the yellows or one on the reddish/orange and one on the yellow.

on 200vac:
1* results: blowing the 5amp fuse by shorting the circuit.
2* results: "0.00" and iirc, it won't allow the inducer motor if I have the probes in place before call to heat is placed. I have to remove one real quick and then it starts and then replacing the probe sometimes creates a spark or ark, can't tell, really fast.

other than that, I will say that the inducer motor comes on really quick from call to heat, maybe...2-5 seconds most of the time? aaaand...it gets up to speed in maybe 1 to 2 seconds at the most. I honestly don't know which wires to check anymore as far as that 24 VAC goes...
 
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Old 11-07-10, 10:59 AM
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The inducer shutting back down in 3 - 5 seconds would have nothing to do with the pressure switch or drafting. But may have to do with the 24 volt from the thermostat, going away -or- a control board malfunction.

What happens if you set your meter to 200 vac and put red probe of meter to W terminal on the low volt wires terminal strip,and put your meter's black probe on a chasis ground or terminal strip C terminal? Does 24 vac continue, or not, after the ID shuts down?
 
  #23  
Old 11-07-10, 06:13 PM
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Originally Posted by ecman51` View Post
The inducer shutting back down in 3 - 5 seconds would have nothing to do with the pressure switch or drafting. But may have to do with the 24 volt from the thermostat, going away -or- a control board malfunction.
oh, idk if I wrote that well enough. I was trying to say that as soon as I turn it to heat and it sends the call it only takes like 2-5 seconds for the inducer fan/motor to turn on. uneducatedly seems like it's in good order...but hopefully (with your next troubleshoot below) I'll figure it out

Originally Posted by ecman51` View Post
What happens if you set your meter to 200 vac and put red probe of meter to W terminal on the low volt wires terminal strip,and put your meter's black probe on a chasis ground or terminal strip C terminal? Does 24 vac continue, or not, after the ID shuts down?
okay, I've blown about 6+ fuses but finally got it right after waiting for it to get up to speed before trying to check it, lol.

results w/ probes connected to W(red) and C(black) and multi set to 200vac:
inducer up to speed: 27.0-27.2
inducer running, click, ignitor heating: 26.3-26.5
inducer running, 3-4 clicks, ignition & flame: 25.8-26.0

WR50A50 still hit me with a 3 flash "pressure switch error" code...in which I just let go of the safety switch and everything shut off.

thank you for helping me figure out how to check that.
 
  #24  
Old 11-08-10, 10:22 AM
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so, I went ahead and did some searching for the 50A55-843 catch-all "upgrade" / universal replacement motherboard/brain/computer... at comfortguru's they have not only lots of useful info, but some troubleshooting info and other helpful documents as well. I know these pages are for the 843 but it's very similar in a lot of ways, including 3 flash code being pressure switch error. So I went ahead and looked through the diagram to see what it may suggest. I wonder if the inducer fan is having some issues, even though it turns on flawlessly, on time, etc...

link: ComfortGurus.com: White Rodgers 50A55-843 Universal Ignition Control Module

843 troubleshooting guide: Troubleshoot Guide

AND a new pics page @ webshots: Trane XE80 NG furnace issue pics

that way I can imbed the pics in this thread. however...I don't really want to to do that right now other than a few since I have 21 pics on there. lol.





and something you guys will appreciate! a buddy of mine hooked me up with this brand spankin new carrier edge tstat ...for free (with a 250 foot roll of wire, lol!!):
 
  #25  
Old 11-10-10, 10:08 AM
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today I started to order a pressure switch from Keith Specialty Store.

I apologize for lack of intelligence to look close enough at the numbers inside the top of the furnace. my model and serials are:

M: TUD080C936H4
S: N0213UM2G


I also found out that the pressure switch I have is NOT the Trane recommended switch for my unit.

Trane rec'd (supposedly) for my model: https://keithspecialty.com/k/68-830.htm
this switch has 4 electrical connections, which I would have no idea what to do without that extra wire being...MIA?

and what I have IN my unit: https://keithspecialty.com/k/68-765.htm
This is what I have...which I may buy. I need to either complete that circuit by jumping them or get like a vacuum guage (don't know where I'd get one to test it...) and see if the switch is bad at .50/.55 to .65 or whatever the range is.

anyways, that's my update. I haven't completed the order yet since I'm in limbo on what to do with these switches...obviously I'm probably not going to be buying the rec'd one since I don't have the one other wire there for it.

sorry again for the mixup in model numbers.

thanks in advance
 
  #26  
Old 11-10-10, 11:28 AM
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If the system hasn't been properly tested --- yours hasn't, replacing the pressure switch has about a 5% chance of solving the problem.

Essentially you are guessing that's the problem without verifying to see if it is or not.

A competent repairman will use a manometer to measure the pressure to see if the pressure switch or some other portion of the furnace is the problem. 95% of the time it's some other portion of the furnace.

But pressure switches are easy for incompetent repairman to replace, so they are replaced by the thousands. Later on someone still has to figure out what the actual problem is.
 
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Old 11-10-10, 03:47 PM
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Originally Posted by walth View Post
okay, I've blown about 6+ fuses but finally got it right after waiting for it to get up to speed before trying to check it, lol.

results w/ probes connected to W(red) and C(black) and multi set to 200vac:
inducer up to speed: 27.0-27.2
inducer running, click, ignitor heating: 26.3-26.5
inducer running, 3-4 clicks, ignition & flame: 25.8-26.0
(I've been out of town the last couple days.) Your tests are correct.

WR50A50 still hit me with a 3 flash "pressure switch error" code...in which I just let go of the safety switch and everything shut off.
Which safety switch?: The blower door safety switch? If you let go of that, of course it would all shut down.

I, or we, need to know what is shutting off, in the normal operation, and what happens to those voltage figures when it shuts off. Need to know what shuts off, and when, and what stays running, regarding the flame and the inducer fan.

thank you for helping me figure out how to check that.
You are welcome for any help.
 
  #28  
Old 11-11-10, 12:49 AM
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yeah well SP, don't really have much to go by. No manual, no help, less chance of quick success. The people that lived here before us for 35 years obviously threw away all the good manuals and left the crappy ones behind (not to mention the crappy repairs!); like one for a 10 year old cd player, one on how to operate a "two button thermostat" and a couple of vague papers for the gas fireplace that mention to stay away from the fire, it will burn you. I don't know what I'd do without you SP, other than the fact that you haven't contributed to my success in the least bit and you also need to comprehend, pretty quickly if you don't mind, the differences of someone who is literally stupid or dense (as you like to say, incompetent) and someone having little to no experience, tools and guidance to fix something, no matter the occasion, level of skill, risk involved or extent of knowledge necessary or learned. As seinfeld would say, "thanks for mutton". lol

>>>>
ecman51',

yeah, the black switch that cuts power when you open up the blower door. I knew it's function which is why I didn't go clicking off breakers, etc while I'm in there. But at the same time I waited until after seeing the 3 flash code to let go of the switch (so that much less was actually running) and because I felt it may mess something up? I could of been wrong...better to be safe than sorry tho

I'll get back to you on voltages and times, but the inducer is always, always, always on. I don't recall it EVER turning off other than when there's no call for heat because the tstat has met the setpoint or I turned it off, etc.

pretty much it's like this:

t-stat set on/auto and heat
call for heat
click; inducer on
click; ignitor heats
2-3 clicks; flame

before I "fixed" it, the flame would go out pretty much as soon as the ignitor cooled but lately it will go for a lot longer; what feels like a minute or more (which is why I say I'll get back to that. I may just do a video). and the ignitor cools down as normal and the flame continues on for quite a while.

then after that while it will click 3-4 times again (which also sometimes provides a burst of flame for each click...) which also shuts off the flame. A brief period occurs with "normal call for heat" blinking and then the pressure switch error 3 flash code and a little bit later it repeats the above. All the while, the inducer is still on and continues in what seems a flawless motion.

I'll try to get up a little earlier today and check this stuff out and maybe make a video too
 
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Old 11-11-10, 09:19 AM
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What's the difference between someone who has no tools, experience, guidance or manuals and someone who is incompetent? But my comments are intended to be descriptive, not a moral judgment. You are trying to do a job you aren't competent to do.

Unfortunately, you have a furnace problem that requires some careful inspection to identify the problem that is preventing the furnace from venting properly. The experience you don't have is important.

Fairly often it's possible to guide people to identify the cause of problems with their furnace. Other times that's not possible to do.

I would be surprised if internet guidance is going to substitute for an expert eye and mind inspecting your furnace for the cause of the venting problem, but I'd be glad to be proven wrong.

Ecman in particular is acclaimed as a genius in helping people. Perhaps he will be able to pull off another miracle for you!


One thing you can do---

Pull off the inducer motor assembly and fan from the furnace ---usually it's held on with a few screws. Check the fan wheel for broken or corroded blades. Inspect what you can see of the heat exchanger for any water, soot, gunk or debris.
 

Last edited by SeattlePioneer; 11-11-10 at 10:03 AM.
  #30  
Old 11-11-10, 10:01 AM
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Are you seriously asking me the differences between the two? You would make an excellent manager of people...your turnover rate (for pissed off people, in case I need to explain) and firing rate (incompetent losers like myself who would have never made it anyway) would put you and your boss out of jobs. You're like...a good mix of mr.scrooge and the grinch. People just aren't smart enough for you, they just "happened" to get it.

sadly too, in your last statement by saying (but not claiming it yourself) that ecman is acclaimed a genius...but maybe, just maybe he'll fluke and happen to get a miracle and solve my dilemma. lol! good call...but sadly, a genius and a "miracle worker" are far from the same. besides, it's not going to take a miracle to fix this, but I am certainly grateful for ecman's vast knowledge, courteous help and hours and hours of time involved.

wow, well, I'm going to go check out this furnace now
 
  #31  
Old 11-11-10, 10:12 AM
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That's promising! Motivation is good!
 
  #32  
Old 11-11-10, 10:52 AM
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right...

so, I just went to the furance, pulled off the tube, pushed in the airbox switch, waited for the inducer to start and then sucked in the plunger causing the switch to complete the circuit. I then waited a little while and then when the ignitor started to glow and it was almost to the firing stage I let go of the hose and everything shut off. so it's definitely not the inducer fan motor's suction OR the switch.

I had originally thought that the switch wasn't being connected but I was wrong, otherwise it wouldn't have been working all the while.

I've got a video on the way
 
  #33  
Old 11-11-10, 11:05 AM
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Trane XE80 cycles with failure

it takes almost 2 minutes for it to complete the first "fail-cycle" lol

and sorry it's so dark, I don't have much light in the basement. Another thought, each time you hear a "blip" in the sound, where it gets sort of silent for half a second, that's the "click" or connection being made to whatever. tomorrow I'll focus more on getting voltages. At least now you can see and hear what's going on...

thanks
 
  #34  
Old 11-11-10, 12:13 PM
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Originally Posted by walth View Post
right...

so it's definitely not the inducer fan motor's suction OR the switch.



I've got a video on the way


Very likely the problem is in the venting system, which includes the inducer motor and fan.

Bypassing this system by disconnecting the pressure switch merely helps confirm this as the problem. It doesn't even rule out the pressure switch as a problem, although that's unlikely as always.

Now you need to identify which of several parts are the problem(s). This can be a defective inducer motor, defective fan, plugged heat exchanger, defective vent pipe, plugged chimney, plugged inducer housing nipple, bad pressure switch hose and so on.

You've completed the easy part which would take a skilled repairman about ten minutes to do.
 
  #35  
Old 11-11-10, 04:36 PM
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Originally Posted by walth View Post

I watched it. Very good video.Typical failure. So why in post #32 did you leave go of the pressure tube? You should have held it for long enough to see if the burner flame would ever go out. Carry out the actual voltmeter test on the pressure switch the entire time. SP made the suggestions as to where the failure might be.
 
  #36  
Old 11-12-10, 01:35 PM
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objective: keep the plunger on the pressure switch backed out away from the switch completely to see if the furnace will run full out non-stop

results: keeping vacuum on the hose the furnace ran for at least 6 minutes before I let the hose go and the furance's pressure switch "fail" which was fine. I was tired of breathing in, lol.

my thoughts:
1. the inducer fan isn't fast enough / needs some lube to reduce resistance
2. the inducer fan is fluctuating causing the switch to fail? (which I negate next)
2. there must be a small amount of leakage in the inucer housing or somewhere in the works, enough to let the pressure switch fluctuate and fail sometimes but most of the time extremely close to that switches connectivity point. While the furnace is running, and working off the inducers vacuum draw, the plunger moves back and forth enough to eventually go too far and fail. which is why I say leakage since it varies...I know it's possible for the fan to vary but I would think it shouldn't vary at all.
3. I checked the hose, put my finger on one end and pulled vacuum through and it's legit that way. but there could be air getting in on either of the nipples from the switch or the inducer housing, or could there?

>> been probably an hour now, went to home depot and looked for some hose that looked about right. 3/8ths OD and 1/4 ID seems to be pretty close. I also bought some hose clamps and tightened those down decently tight so I can say the hose isn't the issue. I'll be taking that hose back, lol

I guess I know now why the switch is positioned "sideways" if I have the switch up so the plunger is pulled down with gravity the switch works great. lol. if it's the other way it won't work at all. I know it's spring operated so it will push back on that switch but it cracks me up too

voltages to the piggybacks seems pretty constant like SP said as long as the inducer is on or whatnot. the "negative" side single is the other side of the switch activated by the suction and that was:

inducer on: 27.7
ignitor glowing: 27.2ish
flame on: 25.9-26.0 varied in that and switched a lot but sounds normal to me.

oh, and when the switch fails, the single "negative" red line that goes to the computer hits "0" until the switch connects again.

well, I'm off to an evening with my wife in Roanoke and to get some car parts I lent to a bud
 
  #37  
Old 11-12-10, 01:49 PM
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Originally Posted by walth View Post
.......... and the furance's pressure switch "fail" which was fine. I was tired of breathing in, lol.
???????? I am in a real hurry to respond to posts, and wording like this prevents me from doing so.

So, the bottom line is that you have pretty much confirmed that it is the pressure switch that is opening, that is causing you the problem. Except you do not know why it opens. Correct?

Just so you know, the vacuum suction is extremely low. Extremely. Therefore, if you see the plunger fluctuate some, that is not unusual considering the weak suction that all furnaces pull on their pressure switches.

But obviously in your case, it is a hair too weak, for some reason. Sucking on the hose will only verify the electrical contacts in the switch work. But is not a good indicator of the condition of the diaphram inside it. However, if you are able to gently suck in on the plunger, then clamp off the hose tight, while in the middle of sucking on it, then stop sucking, and while the clamp is on it...... then not see the plunger retract - then that would also mean the diaphram is good, and that your problem is not likely to be the pressure switch, but how the furnace draws.

I can't remember, but did you make sure that both ends where the vacuum hose plugs in is clear? Have you made sure that the exhaust vent is clear and if you have an intake vent, that that is also clear? If you have a sealed combustion chamber, try to open up the cover to it and run it with the cover off to see if it stays running then. Have you blown out the condensate both towards the drain and also then back into the furnace? If you have not done any of these things, then do so.

I just got a call and have to go out on 2 more jobs, so I will have to come back later.)
 

Last edited by ecman51; 11-12-10 at 02:09 PM.
  #38  
Old 11-12-10, 09:14 PM
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to start off with what you quoted, I was inhaling to keep up the vacuum every 1-2 seconds for those 6+ minutes...I was tired of doing so, let go of the vacuum and it clickity clicked and the flame went out, inducer stayed on, 3 flash code, did the same thing it did in that video I made and was ready to go again and then I let go of the blower fan door switch as well and turned it off. But there wasn't any issue the entire 6 minutes. and the voltage was fine as well

yeah, idk, it just might be the pressure switch. I was sucking the plunger ALL the way back up into the switch housing and then using both hands to clamp the hose twice and it was STILL losing vacuum. I was thinking about taking some vice grips and a paper towel and folding the paper towel up pretty good and then clamping over top of that so it would make a pretty unstopable seal and see what it does then...

as far as cleaning goes:
1. the nipples to both are clean as I blew through the hose into each the inducer area and the PS and they seem fine.
2. The exhaust is clean and clear, I blew that out with a powerful shopvac.
3. I don't think this furnace has an intake so-to-speak. does the inducer motor "create" intake by drawing air through where the burners are?
4. sealed combustion chamber...I mean, there could be one, but if there is, I have no idea how I'd get it off without first taking off the gas system, etc to get to it. which would be a PITA to do just to get it run without it being on.
5. I'm guessing this is what you'd call the condensate pipe, yeah? (I only ask because of technicality and confusion in earlier posts...) In this pic, this pipe on the left leads to a drain in the floor and the upper left cap isn't cemented on and when I take it off boatloads of air come from inside the furnace. I'm guessing the function is to push the water out?


UPDATE>>>

I just went down to the basement and put the other hose back on the switch, papertowel, needlenose pliers, vacuumed it up, kept pulling vacuum, clamped down hard, kept drawing to where it was pulling my tongue into the hose and yet the plunger still came back out and failed the switch. I did this several times over with the same results. I also made sure that the hose was ALL the way on the switch nipple. and besides, I put that clamp on for the other hose and it was still failing with it death-gripped on there...
 
  #39  
Old 11-12-10, 10:35 PM
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Just a warning----

Pressure switches have a delicate membrane that senses the pressure. Sucking on a pressure switch is a good way to break the membrane or stretch it so that it is damaged and will no longer accurately measure the pressure it should, which can create safety hazards.

I'd recommend against sucking on pressure switches. The correct way to test pressure switches is to use a manometer to measure the pressure in the sampled area and determine whether the pressure switch is closing properly with that pressure.
 
  #40  
Old 11-13-10, 12:07 AM
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Originally Posted by SeattlePioneer View Post
Just a warning----

Pressure switches have a delicate membrane that senses the pressure. Sucking on a pressure switch is a good way to break the membrane or stretch it so that it is damaged and will no longer accurately measure the pressure it should, which can create safety hazards.

I'd recommend against sucking on pressure switches. The correct way to test pressure switches is to use a manometer to measure the pressure in the sampled area and determine whether the pressure switch is closing properly with that pressure.

I agree with SP on this one and it don't take much to get them damaged at all.

Merci.
Marc
 
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