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American Standard control board flashing 3x

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Slowhand63
Slowhand63 Member Posts: 80
It's a large, old, poorly insulated house, heated by two American Standard 105,000 BTU 80% efficient approx 10-year old furnaces. They are twinned together and I refer to them as F1 and F2.

Several days ago I noticed the furnace was running for an extended period of time (20-30 minutes) without reaching the thermostat setpoint. Upon investigation I found F2 control board flashing 3x - indicating a pressure switch issue. The good thing about having two identical units is that it allows swapping of parts for troubleshooting.

I swapped the Honeywell pressure switch - no change, then the induced limit switch - no change, and ultimately the inducer. When I swapped the inducer the error code moved with it from F2 to F1.

Initial diagnosis: inducer needs to be replaced. I ordered a replacement which should come in a couple of days.

BUT... this morning the unit was running forever again - and I find no flame in F2 and the control board flashing 3x. What???

I should also note that this is an INTERMITTENT problem. The error code will appear occasionally, and the unit with the error will have no flame. Even with the error code and no flame, it sounds like the inducer is running (though a little difficult to tell).

Each unit is piped separately, so it's not a clogged pipe. It's not logical that there would be an intermittent failure of BOTH control boards, or BOTH inducers at the same time.

What else could it possibly be?

Any/all suggestions/advice greatly appreciated!!!!

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Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,426
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    Check all your wiring for loose connections or even broken wires. Undo, clean, and redo all connections. Check your grounds.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Thanks for the response/suggestions - I will. There is a single ground wire that terminates at the pressure switch bracket. I am pretty sure that's secure. Most others are multiplugs, or stake-ons, which seem pretty secure. The only exception are the two black wires to the limit switch mounted on the inducer which are spliced with wire nuts. If a "loose wire" is the culprit this is the most likely location. I will verify ALL.

    As detailed in my first post, I had the 3-flash error this morning about 7:30 and shut the system down. Two hours late I powered the system up and it ran fine. I didn't touch anything other than the on/off power switches on the sides of the units. I find it odd that the problem appears intermittently and can be corrected/reset with a simple power cycle.

    A note of clarification on my first post... the potentially problematic inducer from F2 is now in F1 (as are the limit and pressure switches). Error code moved with the inducer to F1 last night. This morning error code appeared on F2 again - though I left the parts swapped.

    I will verify all electrical connections - but also welcome any other ideas/suggestions.

    Thanks.
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Brief update… since the 9:30am power cycling both units have been running fine all morning (3-1/2 hrs) without doing anything…  I plan to ensure tight connections on all wiring but I’m waiting to see if the problem reoccurs.  Intermittent issues can be frustrating. 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
    edited January 2023
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    If you want to double check the 12 pin Molex plug connection, you want to pay particular attention to pin #7 and #10 as shown on the wiring diagram. This is because power is sent out from the control on the yellow wire from pin #7 and must return to the control thru the orange wire on pin #10 for the control to go to the next step in the sequence of operation. If that does not happen within a predetermined time limit, a 3 flash error code is displayed.


    So check those 2 pins for good connection, then see that the orange and yellow wires are properly connected to the air pressure switch by removing and replacing the spade connector to form a new friction burnished connection to the metal male spade and the female spade connector. This action of unplugging and plugging in the wires can often refresh otherwise high resistance corroded wiring connection.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Slowhand63
    Slowhand63 Member Posts: 80
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    Ed - many thanks for your response.  The spade connectors have been on and off each unit probably a half-dozen times each - but easy enough to pull them off and perhaps apply a little steel wool to the p-switch terminals.  The fact that I’ve swapped the switches and the issue didn’t move - then moved when I swapped the inducer - then moved back to the orig unit with the inducer in the same place makes me a bit skeptical.  Also at one point I popped in a universal P switch that didn’t solve the problem. I’ve been hanging around all day waiting for the issue to reappear and so far it has not.  Thanks to those that have responded giving me a couple of ideas/things to try.  Please keep them coming!
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,101
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    I commend your efforts, but its probably time to call in a good, local gas furnace expert.   Its easy to fry perfectly good controls swapping around like that. I recently spent 6 or 7 hours in my own house troubleshooting my radiant boiler controls.. I got 95% there and had to get heat back on and for $200 bucks it was in an hour by a controls expert I know.   Almost a whole day lost.  Mad Dog 
    jpm659er
  • pedmec
    pedmec Member Posts: 987
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    check all the drain hoses from the collector box to the internal trap. the collector box will fill with condensate until the condensate plugs the vent hose that is connected on the lower end of the collector box and connects to the pressure switch. then stick a small 18 gauge wire into the connection at the collector bx to make sure that it is clear of debri. It sounds like you are having a drain issue in the collector box as it will slowly drain out of the collector box when it is in failure and then when the unit is able start up again until the condensate backs up again.
  • Slowhand63
    Slowhand63 Member Posts: 80
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    pedmec - thanks for the suggestion.  I didn’t think it was related to a clogged drain since at one point moving the suspect inducer from F2 to F1 resulted in the issue moving with the inducer - and how could BOTH drains suddenly be clogged?  I also remember hearing the Little Giant condensate pump click on at one point… but with your suggestion, and the more I think about it - at one point the twinned unit drains due tie together as I do have a single condensate pump.  This is a good suggestion and I will check all drain lines in the morning and report back.  Thanks. 

    Also of note that the furnace ran all day without issue.  2 or 3 times this week I noticed the issue (one side running - “3-flash” code) first thing in the morning.  Either it occurred during the night, or on the first long heating cycle as the thermostat changes from 65 overnight to 70 in the morning.  I suspect I’ll see it again in the morning.  
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,101
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    Intermittent problems are the hardest to solve. Mad Dog. 
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Well, as expected, I once again experienced the 3-flash error code on F2 first thing this morning. It seemed to run fine all day - but is tripped during the extended heating cycle first thing in the morning (though it is possible that it happens sometime during the night while I’m sleeping and isn’t evident until the morning). 

    I powered the units down and began to investigate. I looked for a plugged condensate line - but the short of it is I didn’t see any evidence of one. 

    pedmec - I couldn’t exactly follow the directions you gave me - all of the drain lines are large diameter black rubber hose. I believe the small diameter tubing that runs to the pressure switch is all air tubing - not condensate. I pulled a couple of the large D hoses - “snaked” them - and saw no evidence of backup or anything plugged. 

    I’ve taken photos to show you what I’m working with and will attempt to post.  

    After the unit being powered down for 90 minutes I powered it up, and like yesterday, the error code is cleared and it’s running fine…
  • Slowhand63
    Slowhand63 Member Posts: 80
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    I had ordered a new Honeywell pressure switch which I installed.  I also double-checked/secured all electrical connections.  I am not hopeful, but let’s see what tomorrow morning brings.  
  • pecmsg
    pecmsg Member Posts: 4,883
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    Personally those pleated filters are too restrictive for proper air flow 
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Does this make sense… ?  I installed the new pressure switch.  Reset the two connections with the wire nuts (didn’t re-strip - the copper looked fine, just resecured).  Started the unit, which ran fine all day - and on the initial cycle I now have the pressure error.  I also noticed that the inducer runs for about a minute, stops for 15-30 seconds, and then runs again (and repeat).  Powered it down…. Checked a couple of the drain lines… powered it back up and now it’s running fine. 

    Is the inducer behavior typical since there’s a pressure error?  Or does the inducer turning on and off indicate some type of inducer/control/electrical problem?  I have a multimeter and spare control board if needed. 

    re pleated filters…. I’ve used them for 20 years. They are on both sides and unit F1 is running fine.  They are changed approx monthly - the last time about a week ago.  If I don’t use pleated filters, what should I use?  And isn’t air flow through the filters completely separate from combustion air?  I appreciate the comment and eager to learn whatever I can, but even if they were too restrictive it wouldn’t contribute to my current issue - correct?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
    edited January 2023
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    Did you get a replacement combustion/exhaust fan/motor yet?

    Based on you Fan swapping experiment, I would concentrate on #1a. 1b. and 1c.
    re pleated filters…. I’ve used them for 20 years. They are on both sides and unit F1 is running fine. They are changed approx monthly - the last time about a week ago. If I don’t use pleated filters, what should I use? And isn’t air flow through the filters completely separate from combustion air? I appreciate the comment and eager to learn whatever I can, but even if they were too restrictive it wouldn’t contribute to my current issue - correct?

    I used them for years on all my customers with maintenance agreements. Anyone that did not have an Electronic Air Cleaner or some other device like the Air Bear. I ordered the Merv 8 because it was the least restrictive to the air flow. Even those with heat pumps where air flow is most important. The see thru spun fiberglass or hogs hair filters let everything but the big stuff thru. You are fine with that filter and the fact that you do monthly changes is even better.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • pecmsg
    pecmsg Member Posts: 4,883
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    Did you get a replacement combustion/exhaust fan/motor yet? Based on you Fan swapping experiment, I would concentrate on #1a. 1b. and 1c.
    re pleated filters…. I’ve used them for 20 years. They are on both sides and unit F1 is running fine. They are changed approx monthly - the last time about a week ago. If I don’t use pleated filters, what should I use? And isn’t air flow through the filters completely separate from combustion air? I appreciate the comment and eager to learn whatever I can, but even if they were too restrictive it wouldn’t contribute to my current issue - correct?
    I used them for years on all my customers with maintenance agreements. Anyone that did not have an Electronic Air Cleaner or some other device like the Air Bear. I ordered the Merv 8 because it was the least restrictive to the air flow. Even those with heat pumps where air flow is most important. The see thru spun fiberglass or hogs hair filters let everything but the big stuff thru. You are fine with that filter and the fact that you do monthly changes is even better.
    And I’m sure the static pressure #’s are close if not within range. Most systems I see that filter puts it over the edge. 
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
    edited January 2023
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    pecmsg said:


    And I’m sure the static pressure #’s are close if not within range. Most systems I see that filter puts it over the edge. 

    I have had some issues with the 3M filter (and other brands) that cost over $20.00 ea. at the big box stores. They ARE very restrictive and the advertise they are 90 day filters. In 20 days on your heat pump, you will start to see a problem with static pressure. (and higher electric usage). I believe that @Slowhand63 is not using those very restrictive filters by the number of pleats. I believe you will agree that his filter choice with monthly maintenance is just fine.

    ...and even if they were too restrictive, that would not have anything to do with his current issue.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    pecmsg
  • pecmsg
    pecmsg Member Posts: 4,883
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    Without TESP #’s we don’t know!
    EdTheHeaterMan
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Thanks all for your comments.  They are all very much appreciated.  

    Ed - to answer some specific questions and to further my education…

    Re the capacitor - when I swapped the inducers the capacitor went with it, which made me think it couldn’t be the capacitor.  Still - it’s an $11 part and I ordered one yesterday as cheap insurance. I can swap it out (after discharging the one in use) when it arrives tomorrow/Saturday.  

    The inducer I ordered - even with expedited shipping, won’t arrive until next week sometime. 

    I do have an older version on the shelf (see photo) that I had swapped in at one point.  I could try popping it in again. 

    I’ve noticed the kink and bend in the hose that runs from the unit to the condensate pump.  When I’ve checked for water by removing the hose from the bottom, there’s a little water trapped in the low point of the bend, but jo water comes out of the collection box when I pull the hose off. 

    Here are my thoughts/questions:

    1. Is the clear tube that runs to the bottom of the pressure switch a water line or an air line?  I’ve assumed an air line. I’ve never seen any moisture in that line on either furnace.  

    2. Is it possible upon installation that the pressure switch isn’t made the first cycle since it’s been disconnect and opened to atmospheric pressure?  That seems to be the experience I had when I installed the new switch this afternoon, and could explain some of the findings when swapping parts to troubleshoot.  If I see an error on the first cycle I would conclude that the problem wasn’t solved and move to something else.  Perhaps I need to wait for several cycles???

    3. The furnaces shipped with, and I have on the shelf, an spare older inducer (see photo). They two furnaces now have a newer version.  The older version does not have an external capacitor.  Does it make sense that I install it to see if the problem clears?  I’ve done this before but I don’t remember if I was patient enough to run several cycles.  

    For now I’m leaving the pleated Merv 8 filters in place (it’s all I have - and I order them 6 at a time from Amazon).  I’m also well aware that electrical and mechanic parts fail from time to time, so if I have the impression that I expect the unit to run forever without a part failing that was not my intent). 

    Thanks to all.  
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Old inducer
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,613
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    @slowhands63

    Just swapping parts without troubleshooting is going to drive you crazy. You need to find the circuit that @EdTheHeaterMan pointed out that causes the three flash error code and check it all the way through.

    Inducers are usually good or bad. If the motor sounds ok and the blower wheel and housing are ok the inducer is probably ok.

    It could be the control board.....it could be anything.

    Look for something simple. Deteriorated tubing, plugged tubing and ports (spiders love those. Just looking at things from the outside doesn't do anything just because it looks the same as it did 20 years ago doesn't mean it's ok.

    When the furnace starts watch the flames carefully and keep watching when the indoor blower comes on and look for any change

  • Slowhand63
    Slowhand63 Member Posts: 80
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    Currently the furnace is running as it should. I checked and I’m getting 24vac as expected.  I need to wait until the error code reappears and I can follow the circuit - likely in the morning. 

    I believe I’m following a logical sequence of troubleshooting.  I got a pressure error - I swapped out the pressure switch, then the limit switch, then the inducer.  I’ve checked the wiring connections and the tubing.  It could be a control board issue (and I do have one on the shelf as I’ve changed them before) but in my experience when they go, they go, rather than fail only on the first heating cycle of the morning and then run fine all day.  
  • pedmec
    pedmec Member Posts: 987
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    the white hose that runs from the the pressure switch to the collector box. the little nipple that it connects to on the furnace collector box. still a pin, small wire, anything into the little pin hole. if any debris gets stuck in theat opening it wont make the pressure switch. #2 on the list
  • Matt_67
    Matt_67 Member Posts: 288
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    If you haven’t removed the white trap (item 3 in Ed’s diagram) and thoroughly cleaned it that is worth a try. Take it out, shake it and run hot water through it.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
    edited January 2023
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    This comment is why I believe that you need the new Combustion Fan assembly.
    @Slowhand63 said:
    ...I also noticed that the inducer runs for about a minute, stops for 15-30 seconds, and then runs again (and repeat). Powered it down…. Checked a couple of the drain lines… powered it back up and now it’s running fine.

    This is not normal for the fan to stop and start and stop and start during the call for heat or during the start up sequence. The capacitor or the wires to the motor are suspect. If it was on the PC control board, then swapping the Combustion fan assembly from F2 to F1 would not move the problem to F1

    Also I was not saying YOU were saying the "All of a Sudden" quote. I just remember customers would want an explanation of why "ALL OF A SUDDEN" the failure happened. I would reply "All of a Sudden your heater got to be 30 years old". LOL. Like when the obituary states "90 year old man dies suddenly" I don't believe something that takes 90 years to happen can be described as "Suddenly!!!"

    Back to your situation. I believe that your motor is the problem, so, if the older fan assembly is known to be in working order, then that would be a good place to start. Why were they removed? just to get the newer design or was there a problem. If I had a good part that was coming off an old furnace I would save it. If it was the cause of a problem, then I would toss it so I didn't get tempted to put it on a customers appliance. My luck would be the customer that got that failed part was 3 hours away and I would need to honor a warranty with a 3 hour drive.

    Also # items 2 thru 6 were for reference as to other causes of the 3 blink error. Anything that can cause the switch to not make in the prescribed time, is a possible reason for the lockout. I just believe it is the motor on the combustion fan assembly.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Slowhand63
    Slowhand63 Member Posts: 80
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    Gentlemen

    Many thanks for your comments and suggestions.  I recognize you are all taking your time to help me when you could easily be doing something else.  Thanks. 

    Not much to report today. I had planned to be up early to watch the initial heat cycle and check voltage at the pressure switch if the error occurred, but I didn’t sleep last night (old age) so when the alarm went off at 630 I simply turned the thermostat off and went back to sleep on the couch.  When I got up I turned the thermostat on… but of course no error this morning.  Watched the unit cycle on and off for about an hour.  All seems fine.  

    The new inducer should arrive today.  Unfortunately the capacitor is showing delivery “between Jan 27 (today) and Feb 2”.  It’s anyone’s guess when it will arrive.  I could swap capacitors to see if the problem moves…  but would like to see the error again and check that I’m getting 24v at the pressure switch first.  

    I snaked the lines again.  

    Considering removing the small white collection box to flush it as suggested. Maybe this afternoon (I’d like to get back to hanging gutters on my garage since the weather is nice today).  I really don’t think it’s a drainage issue, but flushing the box can’t hurt and might prevent an issue in the future.

    The old inducer is on the shelf because the installer (who was terrible!) was troubleshooting a different issue and replaced it years ago.  It didn’t solve the problem he was working on (that’s a long story!) so I kept it. I believe in keeping a full complement of any potential failure parts and have control boards, switches, sensors, etc etc on the shelf.  They aid any troubleshooting I do on my own, and make repairs done by others go quickly should they not have a part I need.  

    The longer this goes on the more I think that the inducer is starting to fail (though I’ve seen comments that when they go, they go). It seems I’m only getting the error now on the early morning extended heating cycle - so I may have to wait until tomorrow before I know more.  

    I’ll post again if the situation changes.  

    Thanks to all. 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
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    The new inducer should arrive today. Unfortunately the capacitor is showing delivery “between Jan 27 (today) and Feb 2”. It’s anyone’s guess when it will arrive. I could swap capacitors to see if the problem moves… but would like to see the error again and check that I’m getting 24v at the pressure switch first.
    The new combustion fan assembly should come with a capacitor. It has all part of the assembly, Fan housing, Fan wheel, Motor, Capacitor... should be all one part number

    Can you cancel the capacitor? I just mentioned it because they are available locally by asking for the Microfarad and voltage rating printed on the old one. And they are only a few dollars each. There I go assuming that everyone knows that. Sorry for the confusion. The Trane part number and the generic are probably a huge price difference.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Slowhand63
    Slowhand63 Member Posts: 80
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    Ed - the capacitor was $11 - so if it doesn’t help me I’ll stick it on the shelf as part of my ongoing replacement parts collection.  I ordered it before you posted on the forum. Between the Trane control board, the Sage controller for my Alpine boiler, etc. I probably have $1000 in parts on the shelf. I also have spare capacitors for my pool pump motors. 

    The inducer arrived and although I ordered the “C4” inducer with the external capacitor, they shipped me the older “C3” version. The newer unit retails for about $80 more, so I feel a little hoodwinked. I can return it if I don’t install it, so we’ll see what happens. If I can get this resolved w/out installing it I will send it back and ORDER the cheaper C3 and put it on the shelf.  

    I’ve been in the basement a dozen times today - the unit is running fine.  I’m wondering if cranking down on the wire nuts, and maybe pulling out the spade connectors on the pressure switch a hair to get the probes of my multimeter in have improved the connections? Maybe?

    Of course, now that I want the error code to appear so I can continue troubleshooting, it won’t. 
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
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    Of course, now that I want the error code to appear so I can continue troubleshooting, it won’t.

    I hate when that happens... That will be $150.00, thank you. Call me if it happens again. LOL

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Slowhand63
    Slowhand63 Member Posts: 80
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    So it’s now been a couple of days (2 or 3) since I’ve seen the error mssg.  As a general rule I believe “if it ain’t broke, don’t fix it”, but in this case I’m going to make an exception.  

    I’m going to pull the suspect inducer from F2, install the new capacitor (that arrived today) and put it on the shelf as a spare.  (I’ll keep the old capacitor “just in case” but label it appropriately). I’ll install the older C3 version that I originally had on the shelf and monitor for a few days. If no sign of trouble the new inducer I purchased will be returned and I’ll consider the case closed.  

    I won’t post again unless the error code appears. Thanks to all that commented and helped me through.  I’d still like to find a reputable local service tech - if anyone has any suggestions please do.  I am located in south-western Suffolk County (Babylon) on Long Island, NY.  I’m best reached via my personal email: bbbabny07@gmail.com.  

    Thanks again,
    B
    EdTheHeaterMan
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,101
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    Have you tried the excellent Robert O Brien of Technical Heating in Mount Sinai?   Hey atleast yiu guyscare both in Suffolk. He will solve this.  He might still be found on FAC here.  Mad Dog. 
    mattmia2
  • Slowhand63
    Slowhand63 Member Posts: 80
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    It’s back!

    After running fine for 3-1/2 days, I’m lying in bed early this morning and I can tell from the duration of the heating cycle and the sound that only 1 unit is running.  Sure enough, I have the 3-flash pressure error on F2.  

    I check voltage at the pressure switch.  24vac on the yellow leg, but only 10vac on the orange.  Does this DEFINITIVELY confirm that it’s a control board issue?  As mentioned previously I have one on the shelf which I can install, but I’d like to rule out any other causes before doing so.  

    On one hand I’m irritated that this is still an ongoing issue, but on the other hand, I’m glad I’m one step closer to solving this (especially before I head upstate in a couple of days and leave my wife alone to deal with this!).  
  • Slowhand63
    Slowhand63 Member Posts: 80
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    I’m hindsight I could have checked that the control board was putting out 24v.  It’s possible that the connection at the board isn’t snug.  I’m going to see if the error is still present and check that.  Anything else I should check?
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Confirmed.  Only 10vac at the molecular connector pin 12 (Ed’s wiring diagram above has a different pin-out - ?  I’ve attached a photo but clearly the #12 pin is labeled “PS” and has an orange wire).  Should I look for anything else before replacing the control board?  

    For the record - Ed was right about this 5 days ago!!
  • pecmsg
    pecmsg Member Posts: 4,883
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    The new inducer should arrive today. Unfortunately the capacitor is showing delivery “between Jan 27 (today) and Feb 2”. It’s anyone’s guess when it will arrive. I could swap capacitors to see if the problem moves… but would like to see the error again and check that I’m getting 24v at the pressure switch first.
    The new combustion fan assembly should come with a capacitor. It has all part of the assembly, Fan housing, Fan wheel, Motor, Capacitor... should be all one part number

    Can you cancel the capacitor? I just mentioned it because they are available locally by asking for the Microfarad and voltage rating printed on the old one. And they are only a few dollars each. There I go assuming that everyone knows that. Sorry for the confusion. The Trane part number and the generic are probably a huge price difference.
    Not a good idea using the OLD uf and voltage ratings, Things do change. Always best to get the information from the new motor.
  • Slowhand63
    Slowhand63 Member Posts: 80
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    I still plan to change the control board, but before I do I’d like to hear from some of the forum experts.  

    Interesting that after having the system shutdown for a couple of hours, I powered it up and it’s running fine again.  I’m still perplexed how a control board can have an error and reset itself and run fine for several days before failing again.  
  • Slowhand63
    Slowhand63 Member Posts: 80
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    One additional thought…. the error cleared itself. However - if I had thought of this earlier when I was still getting the error code, I could have jumped 24v from the yellow to the orange lead at the pressure switch. I’m thinking that if I did that the inducer would have started immediately and the furnace would have run. Correct?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,053
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    One additional thought…. the error cleared itself. However - if I had thought of this earlier when I was still getting the error code, I could have jumped 24v from the yellow to the orange lead at the pressure switch. I’m thinking that if I did that the inducer would have started immediately and the furnace would have run. Correct?

    Do not apply 24 Volts to the yellow and orange. This would be a mistake and possibly cause a short circuit that will damage the control or fry the transformer. When the orange and the yellow connect at the pressure switch it is because the fan is already operating. Connecting the orange to the yellow at the pressure switch with a jumper wire would not bring on the fan motor.

    In all of the posts you made have you said that you installed a NEW Combustion fan assembly.

    You need a vent fan/motor assembly complete, without robbing any parts from old stuff. You already confirmed this when you did the swap and the problem moved. Do you understand? You need to replace it with a new, unused, Factory fresh from the manufacturer, an unsealed box, never handled by human hands before. pristine, known good, including all the factory stuff including the little silica packet to absorb moisture during shipping. I don't know how to be more clear. I am trying to be as understandable as possible. I will offer no other possibilities. Only the new combustion fan assembly will solve your problem.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Matt_67
    Matt_67 Member Posts: 288
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    The control board on that furnace checks for an open pressure switch before it starts the inducer. If it’s closed without the inducer running it won’t even start the inducer and will give a pressure switch fault. I’m hoping the pressure switch that was replaced was an oem part from Trane, it’s not a great idea to use aftermarket pressure switches. I would also make absolutely certain that your exhaust and intake are clear and pitched properly and that all potential condensate drainage issues are eliminated. Ed’s right on the inducer too, that should come as an assembly complete and could very well be the issue. I think MadDogs advice is excellent as well, a tech with a manometer and amp clamp would be helpful.
  • Slowhand63
    Slowhand63 Member Posts: 80
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    Installed the brand new, right out of the box not modified no parts swapped inducer.  The furnace had been running fine all day (after the early morning error mssg).  Immediately upon startup with the new inducer the 3-flash error mssg appeared.  Powered it down - waited 5 minutes - powered it up - same.  Removed the new inducer and put the old one back in. No error message.  

    None of this makes any sense, right?

    In response to other questions/comments - the pressure switch was replaced with the exact same manufacture installed Honeywell switch (not a universal switch).  

    I’m back to the control panel - no?
  • 109A_5
    109A_5 Member Posts: 1,387
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    Hello @Slowhand63,

    I check voltage at the pressure switch.  24vac on the yellow leg, but only 10vac on the orange.

    Since apparently the Pressure Switch contacts should be closed (touching and making a good electrical connection) with appropriate inducer pressure applied to the Pressure Switch resulting in the SAME Voltage on either side of the Pressure Switch contacts (using Ground as the meter reference).

    Sounds like the Pressure Switch contacts have intermittent high resistance or the air pressure generated by the inducer is marginal (poor Pressure Switch electrical contact pressure) or there is an air leak resulting in marginal air pressure seen at the Pressure Switch or the Pressure Switch diaphragm could be intermittently leaking.

    For your entertainment;
    How To Repair A Furnace Control Board and Save Hundreds
    https://youtu.be/aYG5TrYlmKs

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System