This is probably a no-brainer but thought I would check just in case.

The furnace is a Coleman TM9V, 96%. We moved in to the house a year ago and had no issues with the furnace (it was only a couple years old). I did replace the leaky condensate pan with the updated pan, but that was about it. This year I picked up a different thermostat to take advantage of the 2 stages (original tstat was only 1 stage).

Four or five days ago the furnace wasn't kicking on. The blower motor was spinning slowly but that was about it. I pulled the panels off before I remembered to look for a fault code. Reinstalled the panels and the furnace started up and returned to normal.

Today it happened again, but this time I watched for a code. 5 red flashes: "Rollout switch or blocked condensate switch is open". I noticed what looked to be fluffy insulation laying beneath the blower motor...weird. After looking a bit closer the fluffy insulation was actually feathers and there was a dead bird stuck in the screen for the intake pipe! Gross!



I pulled the intake pipe completely out and flushed it with water to get the remains out. Furnace is running fine now and I plan on putting some screen on the intake/exhaust pipes outside the house...why the original installer didn't do that I don't know. I actually remember my inspector mentioning I should have screens on them, but I forgot.

Anyways, I'm guessing that was my problem and the rollout switch was tripping? I'm thinking I need to remove the exhaust pipe and make sure it is clear as well...

 

Yes, that was definitely more than likely your issue since it has cleared up after removal of the dead bird. If you install screens on the pipes ensure they are not too restrictive.

 

Thanks for the reply. Figured it was. It was just weird that it ran for 4-5 days before it faulted the 2nd time. Anyways, I just have some 1/2" hardware cloth that I'll cut to fit and then wedge into the pipes. Then I'll just wait and see!

 

There may still be some debris from the bird inside of the inducer.

 

Well, I woke up today disappointed to see the furnace not running, throwing the same code as before. It has been 2 weeks since I got it back up and running after cleaning out the intake pipe. The temps have dropping, so we have been using the furnace quite a bit, without any issues.

I have only cleaned out the intake pipe (and added coarse screens to the intake/exhaust)...I have not touched the inducer or exhaust pipe. Wondering if that is the next step? Kind of a pain to diagnose the problem when it can be two weeks in between each fault...'

Unless there is another bird in the exhaust, I don't think the bird that was in the intake would cause any more problems. There were only feathers that made it beyond the intake screen; the blockage was from the carcass sitting on the screen (see my picture in my first post). A lot of feathers were sitting beneath the inducer motor (inside the housing) and actually didn't make their way into the combustion chamber/inducer.

I'm stumped...if this was happening more often it would be a bit easier to diagnose.

 

The screens could be part of the issue you are experiencing. The screens need to be able to keep birds and other stuff out, yet admit adequate air in and exhaust out. It is possible that you had a build up of ice/frost on the screens to partially block off the pipes just enough to cause the problem. I suggest you make sure there is no frost/ice on the screens and then try the furnace again to see what happens. You may need to replace the screens with less restrictive ones. If that doesn't correct the problem I suggest you check inside the inducer. A few feathers could block the port where the pressure switch attaches.

 

The screens are 1/2" hardware cloth...about as free flowing as you can get. Also, we haven't got down to freezing temps yet this year, so no worries about ice/frost, though I have read about people having that problem.

Reset the furnace this morning and it has been running fine since then. Time will tell if it faults again.

At first I didn't think feathers/debris could make their way into the inducer and exhaust since they would have to travel through the heat exchanger, and thus burning up. But, I forgot that the inducer runs for some time before ignition...so there is a chance of a feather blockage downstream of the intake.

If I remove the inducer, would blowing it out with compressed air be the best method? Same thing with blowing air through the heat exchanger? I would remove the exhaust pipe and flush it out with water.

 

I would wait to see if it faults again before removing the inducer for inspection. If anything, I would check the pressure switch hose to make sure it is clear all the way through and the port on the inducer where the pressure switch attaches to make sure a small piece of feather is not clogging it up a little. If it faulted again, then I would remove the inducer for inspection and cleaning. Low pressure compressed air will work fine.

 

I did not do anything (cleaning hoses) since my last post, but the furnace faulted twice since then...once last week and once today. I removed all the hosed for the three pressure switches and made sure they were clear (they were) and also blew air into the ports on the inducer side.

But then I got to thinking: it is not the pressure switches that are causing my fault. According to the code (5 red flashes) it is the rollout switch or blocked condensate switch. After a little research I found out that the two rollout switches are manual reset switches, and since I never manually reset them it makes me think they have never tripped. I pulled the wires to the rollout switched and checked continuity and everything was normal (i.e. not tripped).

I just checked my furnace's manual and came across more info about the 5 red flashes:

This means that any of the limit switches (main limit switch, rollout switches) can be causing this fault...as long as they are open for >15 minutes. Because neither of my rollout switches have ever been tripped (even during the bird incident), it leads me to believe that it is the main limit switch causing problems. Also from the manual regarding the 4 red flashes:

So, with all that, my initial theory is that my heat exchanger is getting too hot (dirty filter, wrong blower speed) since the fault seems to only occur when there is a call to the 2nd stage. BUT, this wouldn't make sense because I can only get code 5 if the limit switch is open for >15 minutes. If the heat exchanger was getting too hot, the limit switch would open/close/open/close as it heated up and cooled down, eventually leading me to code 4.

I'm trying to think of how the limit switch could be open for more than 15 minutes (but then be fine when I reset it), and I'm not sure how unless the switch is faulty. Maybe it is taking more than 15 minutes to cool down and close? Seems unlikely since the blower motor runs continuously after the burner shuts off from the limit switch opening.

I'm beginning to think the bird incident was just a coincidence and the real problem stems from the fact that I installed the new thermostat that utilizes the hotter burning 2nd stage...

I will have to ponder this some more...

EDIT: Another thought. If it is the from the limit switch getting too hot, I would expect this to happen every day when the 2nd stage is called. By it happening periodically it makes me think the limit switch is either faulty or (just thought of this) the blower motor is not turning on for some reason. Still though, that is saying that the limit switch takes longer than 15 minutes to cool down once it is tripped and the burner turns off....

Could be a loose connection to the limit switch, but the connectors were/are tight. I don't think this is it because I would expect to have issues getting it running again after a simple power cycle.

I should also note that the three pressure switches are monitored separately and will throw their own corresponding code when tripped; so I know my issue isn't coming from the pressure switches.

 

I suggest you try letting the control board control second stage again and see if your issue continues. What type of air filter are you using? Sometimes a filter that is too restrictive can cause the limit to open.

I suggest you test the temperature rise during 2nd stage operation. The blower speed may need to be adjusted. In the linked manual: http://www.havenhomeclimatecare.ca/w...all-manual.pdf

Check Adjustment of Temperature Rise and Variable Speed Motors sections on page 33.

 

The staging jumper was set in the OFF position, so with the previous thermostat the furnace only operated at low fire. I suppose I could change the thermostat to operate as 1H and then set the jumper. What is the difference between my thermostat calling for the 2nd stage and the control board calling for the 2nd stage?

The air filter is the thick Honeywell FC100A1003 16" x 20" x 4". It is probably about time I swap in a new filter, anyways. But, if it was/is restricted air flow causing the problem, the limit switch would open (overheat) and then close (cool down) and continue to open/close until it throws code 4...

I will definitely do this tonight. I read about doing this but never checked it because I assumed the installers set the fan to the correct speed (probably not, though). I'll report back.

If this problem was repeatable it would be pretty easy to diagnose it, since I could just see if the limit switch is open. But because I have no idea if/when it will fault, I can't do much.

Thanks for your help!

 

Here is a link to a thread that discusses an issue similar to yours: http://www.doityourself.com/forum/ga...rmostat.html#b

The person at post #11 has the same furnace series as yours and describes how there was a delay in the blower coming on when both the 1st and 2nd stage heat were called and caused some issues. He stated how he was able to correct that issue. There is a link to a York service bulletin in post #1 that cover your furnace series. There is some great discussion about how thermostats work to control 2nd stage heat. Just thought it may be worth looking at to see if you have that control board listed in the York service bulletin and possibly the cause of your issue.

 

Thanks for digging that up! Good info, especially with the discussion about how the 2 stage thermostats work.

It sounds like the problem he was having was that the 2nd stage was being called (a few seconds) before the inducer kicked in, causing rollout and tripping the switches. This is with the replacement board. The bulletin, regarding the original board, indicated that the call to high and low were simultaneous which caused the blower fan not to turn on (in turn causing overheating).

It also sounds like his problem happened every time, unlike mine. I haven't had a rollout switch trip, yet, so I'm not sure if I'm having the same issue. I'll try to monitor what the thermostat is doing when a call to the 2nd stage is made. I wasn't aware that the low stage would be called first.

I'll be testing my temp rise as well as the limit switch when I get home tonight.

 

I understood that only the limit switch (self-setting) could trip as described below:

From the York bulletin:

"Symptom: When the thermostat comes out of night setback (or the desired set point is set far above the space temperature), the thermostat calls for first and second stage heat simultaneously, which interferes with the programming of the variable speed module. The blower programming becomes "confused‟ whether to run on Hi-Heat or Lo-Heat, and does not initiate blower operation. The primary limit opens, interrupting the heating cycle. If the primary limit remains open for 5 minutes, a hard lockout results".

 

You are correct. This was the issue with the original control board. The guy mentions that he had the board replaced with an upgraded board, and that was when he was having issues with the rollout switches tripping from the 2nd stages engaging before the inducer (post #11).

Still, the fact remains that I am getting code 5 (limit switch open for 15 minutes). I wonder how long it takes the limit switch to cool down (without the blower motor running). The limit switch is a 140F switch. So, the heat exchanger heats up to 140F (and probably a bit beyond), the limit switch trips, heating is cut, and the limit switch begins to cool down. Seems like it should cool down below 140F within 15 minutes, but maybe not...

 

I checked my temperature rise tonight and it is within spec.

Low Fire: T_in = 71F, T_out = 112F, Delta_T = 41F
High Fire: T_in = 68F, T_out = 119F, Delta_T = 51F

The spec for both low and high fire is 35F-65F rise, so it seems I'm good. The "HEAT Tap" jumper is set to the factory A position, which gives max air CFM for high and low.

I also pulled the limit switch and tested it by placing it in a pan on the stove and gradually heating it up while measuring the temperature with a thermocouple. The switch popped open at 144F, and then closed around 98F. So, it appears to be functioning correctly.

When closed, I get a reading of 8 ohms across the switch. I was also curious how long it takes for the switch to cool down and close, so I heated it up again until it tripped and then pulled it out the pan and set it on the counter. It took about 40 seconds to cool down enough to reset.

I'm not sure where to go from here. Only other thing I can think of is to disconnect the blower fan to intentionally cause overheating just to see if I can get code 5 (i.e. the limit switch takes longer than 15 minutes to cool down and reset), however I don't really want to force the thing to overheat.

 

With wires removed and switch cool, the switch should get a reading of 0 ohms if closed.

Have you checked the 12-pin molex connector on the control board? A pin that is pushed out or sticking in more than the others will cause issues. Check the connector for corrosion and clean as required. I also suggest that you check for continuity between pins 11 (red/whiter)and 12 (orange/black) on the 12-pin connector as that is the limit switch/roll-out circuit. Also check continuity between 4 and 10 (ground). Make sure all grounding connections are clean and tight. When furnace is in operation you can check for 24V between pins 11 and 12 while plugged in.

 

The DMM I have at home is pretty cheap; I just measured the resistance of the leads and it came out to 9 ohms. So, the switch is actually 0 ohms like it should be.

I'll bring a better DMM home from work today and take the readings you suggested, as well as check all connections and grounding connections.

 

Here is a color coded diagram of the test points. For me, color coding makes it easier to see the path.

Ground--4 to 10
Limits--6 to 11
Limits plus P/S1 and P/S3
P/S2--1 to 2

 

Great! Thanks for taking the time to help me out with this! I also posted this question over at the hvac-talk forum but didn't get much help before the moderator closed my thread with the reason being, "You've gone further then you should have. And further then our rules allow DIY to get involved with." Why the hell do you have a DIY section on your forum then?

Another thing I have been curious about is that the label on the door panel for code 5 says "Rollout switch or blocked condensate switch is open". So according to that the condensate switch (P/S3) can cause a code 5, but according to the manual and the circuit diagram it can't. An opened P/S3 will throw the same code (code 3) as an opened P/S1 since they are in the same circuit. I confirmed this when pulling connection off the pressure switches during operation.

Anyways, thanks again and I'll check connections tonight.

 

Normally the information that is attached to a unit is specific for that unit and more accurate. Installation guides cover the whole gambit of models so manufacturers will normally attach the more specific info. As I understand it: P/S1 is for 1st stage, P/S2 is for 2nd stage and P/S3 is to monitor condensate. P/S3 has it's own circuit. By checking those test points shown in the diagram it will hopefully isolate the problem.

Did you check to see if the condensate drain system is not clogged up or restricted? Sometimes a partially clogged condensate drain will throw a flash code and then start draining again to reset the system and continue the cycle.

 

The info on the unit sort of contradicts itself. While it says that blurb about the code 5 on the panel, the circuit diagram on the panel is the same as the one in the manual and the one that you posted. Here is a picture of the info on the panel (click to enlarge):



I unplugged the P/S3 during operation to simulate a P/S3 fault and ended up getting code 3. Maybe an extended P/S3 fault leads to a code 5? Neither the panel or manual mention that. I guess that is a test I can do.

As far as checking the condensate drain system, all I did was pull the hoses for the P/S3 and make sure everything was clear there. I also looked into the drain pipe that leads outside and that looked fine. Water definitely trickles out when the furnace is running. Anything else I can do beside pulling the condensate pan?

 

Those contradictory labels definitely make it difficult to decipher what may be happening. Is your control board the one that has up to 13 red flash codes and 4 amber codes as shown in this manual?:

http://www.upgnet.com/PdfFileRedirec...UIM-A-0114.PDF

As far as the condensate drain system does it have a trap inside? Some furnaces have a trap that gets all gunked up. Sometimes the collector box gets gunked up also and if you pull the drain hose off water will rush out. I like to use a shop vac to suck out all of the drain hoses and pipes on a regular basis. Most people don't realize how much condensate is produced by these condensing furnaces.

 

My control board looks a bit different than the one in the manual you linked to. The manual that I have been looking at can be found here (though it looks like the website is down right now):

Coleman Heating and Air Conditioning
http://www.colemanac.com/PDFFiles/10...UIM-A-0114.PDF

My control board looks like this:


I do not have a condensate trap, just the condensate pan that drains into the pvc drain pipe. Here is a picture when I had it partially disassembled to replace the defective condensate pan (defective pan is clear, upgrade pan is black):



The port for P/S3 is on the lower left of the condensate pan, next to the white label. The other hose coming out of the bottom plugs in at the pipe coupler where the inducer hooks to the exhaust pipe.

I guess I can check/clean out the main drain hose. But before I do that I want to try to see if I can get a code 5 from pulling the plug off P/S3 for an extended period of time.

 

I didn't get a chance to check any connection/continuity yesterday, but I did do a couple tests.

1) With the furnace running, I pulled the wire to P/S3 to simulate a blocked condensate switch. The flame was stopped and I got a code 3. The inducer and blower continued to run, and eventually the blower stopped. After 30 minutes I was still getting code 3. So that confirms that I cannot get a code 5 from a blocked condensate switch, contrary to what is said on the the panel information.

Also, it is obvious by the wiring the P/S1 and P/S3 are wired in series, just like the circuit diagram says.

2) With the furnace running, I pulled the limit switch to simulate overheating. The flame was stopped and the inducer and blower continued to run. Initially got a code 4, as expected. After 5 minutes, it went into a hard lockout (code 11). After 15 minutes, it flashed a code 5, as expected. The inducer continued to run. This is the same scenario I would see when the furnace faulted on its own. *EDIT* During this test the blower eventually stopped, but I don't recall when...sometime before code 5 *EDIT*

I think I confirmed at least that if the limit circuit is open it operates the way it should. Doesn't really get me anywhere, though. Pending some continuity checks and checking wire connections, the only thing I can think to do is try to take some measurements when the furnace faults on its own. But, given the fact that I have always done a power reset and the furnace starts right up, I doubt I will see anything with the rollout switches or limit switch.

 

Still trying to help find a diagnosis/solution:

From post #1:

From post #25

See attached excerpts from installation manual. Do you think the issue may be caused by a blower motor problem? I suggest you inspect the blower motor plug to make sure it is fully seated as they will sometimes vibrate loose.

 

Sorry, there was a typo in my first post. When I said "blower motor", I actually meant "inducer". It seems I can't edit a post that old. Basically every time I have found the furnace not running, the inducer has been running and flashing code 5. No blower. Same results as my test #2 from my previous post.

I suppose it could be the blower motor, but that comes back to a question I had before. In order to get to code 11, the limit switch must be opened for 5 minutes (i.e. not cooled down below ~100F according to my tests)...okay, I can believe that. In order to get to code 5 (my case), the limit switch must be opened for 15 minutes. Maybe that is possible, but I feel that it is unlikely...even without the blower running the inducer is still pulling heat out of the heat exchanger.

One way to figure it out would be to disconnect the blower and force the limit to open (overheat) and then see how long it takes for the limit to close...I don't really want to do this unless you think it won't harm the furnace. I mean, that is what the limit is there for, and I verified that is is working (i.e. opens at 140F).

I will check blower motor connections.

 

After reading your last post a question comes to mind: is your blower actually running? On your furnace, the blower is supposed to start up 30 seconds after the gas valve opens, if a flame is detected and continue to run until the thermostat breaks the R-W connection. Another thought: The indoor fan motor is energized through the W1 heat terminal and runs on the speed selected on the HEAT tap of the control board. Some thermostats have jumpers or need to be configured in the installer's set up how the blower is controlled.

 

Yes, the blower is actually running. Otherwise my house would be a bit chilly The only time the blower hasn't run is when I get a code 5. I believe the blower quits running once it enters into code 11...I'd have to redo my test to confirm that.

The thermostat is a Honeywell RTH4500D.

The setup was pretty self explanatory. I'll go through it again to confirm I have all the codes set correctly. But I have a feeling if something was wrong with the thermostat setup the problem wouldn't be random like it is.

 

Just wanted to make sure as code 11 according to the installation manual is usually caused by a failed blower motor or blower wheel. Of course, just because it is running doesn't mean it is operating properly.

The most critical settings are for functions 170 and 180.

 

Just to be clear, I have only ever found the furnace in the code 5 state. It has never been stuck in code 11 (which of course would point to the blower motor as the culprit).

The only time I have seen it in code 11 is during my last bit of testing when I simulated an open limit switch. It only stays in code 11 if the limit switch closes between Time = 5-15 minutes. The sequence from code 4 to code 5 is as follows:

1) T=0 min - Limit opens, flame stops, inducer & blower run. Code 4
2) T=5 min - Limit open still, inducer running. Blower stops. Code 11
3) T=15 min - Limit open still, inducer running. Code 5


I will double check the thermostat settings, but they should be set at 170-9 and 180-0 (170-8 will work also, since I don't have cooling).

Do you think there is any harm in disconnecting the blower, causing it to overheat? If I can prove that I can get a code 5 with a non-functioning blower motor, then that opens up a new realm of possibilities. Just don't want to do something that will potentially harm the furnace.

 

To get code 5 thrown, it would seem it would take a minimum of 15 minutes and only after code 4 and code 11 were thrown.

Based on this data, if the limit opens Code 4 should appear first and burners shut off and only the blower and blower should be running.

It would appear that code 11 would not appear unless code 4 had already been thrown.

Code 5 would not be thrown unless code 11 had already been thrown.

Have you ever observed Code 4 during operation?

With the blower going and the inducer both running with no flame present, the limit should not take very long to cool off and reset.

 

Correct. My idea with unplugging the blower is just to prove that a bad blower cannot cause a code 5 (i.e. the limit switch will cool down and close in less than 15 minutes after overheating).

This did give me another idea. Since the furnace MUST go through code 4 and 11 before reaching code 5, I should be able to retrieve the fault codes using the LAST ERROR button. This would verify that I do in fact get code 4 first, then 5 minutes later get code 11, then eventually get code 5. I'll just have to clear all the current codes and then sit and wait for the next fault.



Correct. In order to get code 5, it must start with code 4 (limit circuit open).

No, I have not. But, I think it would be a good idea to clear all my codes and then occasionally check for any codes. If I end up seeing a code 4 (but not code 5) then that will tell me my limit opened but was able to shut within 5 minutes, indicating an overheat event.

I agree. Even if the blower isn't running (but the inducer is) I would expect the switch to reset before 15 minutes.

 

It would seen that even with the blower not running the limit would cool down sufficiently to re-set before 15 minutes passed. I would assume that if a roll-out switch actually opened it would throw a code 5, correct?

Your control board is definitely more sophisticated than most. About the only way to see really what it is actually doing is to "camp out" until the first code appears. But, that is a good idea to clear the fault codes and then check periodically to see which codes have been thrown. If you check it often enough it would help pinpoint the timeline. I would be curious to know if the inducer and blower are coming on if it actually does throw 4 flashes,

 

My exact thoughts as well. Yes, a roll-out switch opening would definitely throw a code 5 because the limit circuit will never be closed again (until the switch is reset manually). I guess that is the beauty behind the design and the time delay between each fault: code 4 -> most likely overheating, code 11 -> most likely a blower problem, code 5 -> most likely a rollout switch. Too bad in my case it isn't that simple.

I confirmed that it does by pulling the limit switch wire during operation (i.e. forcing a code 4).

I will check connections next, and do some continuity checks. After that I'll clear the fault codes and just wait, checking daily to see if any new codes have been thrown. Maybe something new will develop...

 

It appears your control board functions properly as so far it throws the appropriate code when you remove a wire from the different controls. Have you removed a wire from a roll-out with furnace operating to see if the board throws a code 5? What are the temperatures your limit control is supposed to open and close? I would definitely check the 12-pin molex plug and all ground wires. I have seen those two items cause intermittent issues many times.

 

Well, I was about ready to post up and say that the issue may have been resolved since it has been two weeks since the last fault (even though I didn't really do anything, besides check to see that the connectors were tight), but just my luck I came home today to see the furnace stopped and flashing a code 5, just like before. Dang it!

Between now and last time, I occasionally checked for faults (using the LAST ERROR button) but didn't see anything. One thing I did find odd was that after getting everything reset, the code 5 was not stored. I pushed the LAST FAULT button when the furnace was idling (no call for heat) and the lights flashed as if there were no codes stored. I figured the code 5 would pop up.

So, another experiment. I cleared the codes and then intentionally forced a code 5 like before (pulling the limit switch wire and waiting 15 minutes). In this case the code was not stored either. I don't know...maybe the code is only stored when the fault is corrected without a power reset.

Back to square one. I think we did a really thorough job of going through all the potential problems so I am at a loss of where to go next. I really don't want to call (and pay for) someone to come out when I'm pretty sure they won't be able to diagnose the problem. Unless you think they can do something I can't? They'll check for codes and check all the limit switches and then what? Would the next step be replacing the control board? So frustrating...

 

Yes, that is certainly frustrating. You have done a notable job of troubleshooting the issue. As we discussed previously a 5-flash code usually indicates a manual reset roll-out switch has tripped. The fact you have not had to reset the roll-out switch would point to the control board as the problem. As I recall, for a 5-flash code to be thrown a code 4 and code 11 should have been present. That seems like another strike against the control board since it doesn't store the codes. It is frustrating when a new part is installed and it doesn't correct the problem. But, at this point I don't know what else it could be after all of the testing you performed.

 

Looks like a new control board is around $125. The real kicker is that all the parts are still under warranty, except the only way to get (free) replacement parts is to pay for a pro to come out and do it. I ran into this issue with the condensate pan I replaced; I called everywhere hoping to get a replacement pan but my only option was to have a contractor come out...sure the part would be free put I would have to pay for labor. So, even though the board is $125 it would still probably be cheaper than having someone come out and troubleshoot it and then replace it. I dunno...not quite ready to pull the trigger on the control board...hoping I might think of something else to test.