Nice explanation. Similar error condition I came cross on Goodman GHM95. After several roll-off limit switch changes and several days intermittent 4-blinks problem on and off. After lots of frustrations I found the problem was on board 12 pins connector. During investigations moving wires was correcting the problem but I thought it was corrected by changing switch. Finally I pull out the connector and put dielectric grease on each contact pins and place it back on board. Now no intermittent for more than one week. Several years ago I had similar intermittent problem with the gas valve connector on other furnace. I remember I applied the similar power contact grease (used by the electrician) and that fixed the intermittent gas valve problem on Goodman furnace. So my conclusion is these furnace control harness connectors pins contacts are not gold or tin coated or not under good contact mating pressure and by time it develops oxidation or loose contacts. The dielectric grease helps to maintain good contact i.e. solve intermittent contact problem. So if you see such intermittent issue then may try this.
I have run across the same issue. Thought the board was bad and went to remove the plus and it fired up(had door switch taped up). Or I may never have solved it. Now I check that first.
Another great video Ted. Keep them coming. I’m a Trane dealer too over a thousand miles away from you yet learning from some of your videos and enjoying watching them all.
Love the videos. Between you and mr.lavimoniere you guy's have the best videos. Straight forward and not a lot of dialogue like a few others on RU-vid. Keep up the great work.
Thanks for making this posting. If I didn't have my Fluke on the flame sensor input when it faulted, I would have been scratching my head for another day. The tech from the local hvac charged me 300 bucks to change out a motor start capacitor without fixing the problem. You helped me fix my problem in less than 24 hours whereas I was left without a solution before. I'm ready for winter!
Thanks for the video im a mechanic and was testing resistance on the whole high circuit and it was fine so I was lost, finding this video helped me find the problem thanks.
Mr.Cook. Excellent tip ,and video! Appreciate your time sir,and showing possible code error on fan - limit.,( computer board), Thank you for explaining and demonstrated in your clip..
Thanks for this video ! Solved my no heat condition this morning by jumpering the blower assembly high limit switch - now I just need to find a replacement
Thank you for the video. I had the same board in my Trane furnace. I had suspected a problem with the board during the summer with the AC but it seemed to start working again. I had already ordered a replacement board but I put it on a shelf. Now the heat was doing what you showed. I tested the sensors (good). I made sure the power was off and replaced the board. (One wire at a time from old board to the new board). We have good heat now. 🙂 I would not do this myself but I'm fairly handy. Lol. I worked for Trane (manufacturing) for 12 years.
Thank you for the awesome video. Exactly the same problem, was going to replace reverse flow limit ,out of stock. Pick up and replaced board (kit) comes with new ignitor. Thanks again Merry Christmas!!
Great video! Helped me troubleshoot & temporarily bypass my switch until the store opens in the morning! I will be saving this video as I have this exact model furnace in the mail part of my house. Thanks!
This is EXACTLY my issue! Even same error code. I'm the home owner, I tested the limit switch which was fine but I replaced it anyways. Board still had same issue and no flame. Thanks! I can replace a part but I'll have the service tech out to wire a new board up.
I carry a contactor off an condensing unit with two long leads on it and I put one lead at "c" on circuit board and use the other lead to test for 24 volts. You don't need to look because you can hear the clicking. I wire them into high limits and you can hear it drop out without holding leads there the whole time. A meter will sometimes show 24v but doesn't tell you how well it will flow under load (amps). A chattering relay in that instance will tell you everything you need to know. When testing many things in a system the relay is soooo fast. Go to a roll out "click" next test other side "click", etc. you can test a lot of things in a hurry without ever having to try and see the screen in a dark or cramped area.
I have used a 24 light across the limit but never thought of using a relay. I will keep that in mind. In this scenario I would have checked the voltage across the limit especially if you jump the limit and it runs normal and then you reinstall the limit and it doesn't work...????? That's where a voltage reading would have told you for sure if the limit is just weak or the preconceived board was the issue.
Ken Thomas Good idea, I would put an ATO fuse or resettable breaker in-line on it, in case of short. ‘Click’ = Good, or ‘Pop’ = oh boy, ‘Buzz’ = check voltages
Great video, thanks for sharing, I really liked following your diagnosis and have the same issue. Thanks also to bunch of commenters here! We were prepping for a pretty chilly night and morning, but then I saw comments like "push on the wire connections to the board" and "flick the chips on the board." I did that and the heat came on! haha We'll have a warm night and a new board tomorrow, so awesome.
I’ve ran into this same issue on a hotshot garage heater. Board was sending out an unstable low voltage signal on the limit circuit, throwing high limit codes. The most annoying part was that power cycling the board made the problem disappear, which is probably what happened in your case too. If you were to measure the voltage to ground on that circuit while it’s showing an error code, you’d probably find very low voltage. I measured as low as 9 volts AC. Took 2 return trips to figure it out, now I know. Catch the problem in the act! Don’t power cycle the board!!
Anti DIY HVAC, You Sir are Quality, do it right, fix the little stuff at no charge, show and tell your experience. Good Customers always appreciate that level of attention, I do the same thing. I usually clean up the equipment too, that helps me see later on if anything else has happened especially with condensate, water leaks and so on. I’m trade as well, licensed Master Journey in De & Md, but Middle East Coast, USA, building codes are a bit more strict, but not as strict as say Massachusetts or California. Y’all southern folks do a lot of stuff with flex and duct board that we don’t because of code. I don’t see it as a problem it’s more a regional building thing, if your house is gonna float out to sea every 20 years in a hurricane why bother? Lol kidding. Duct board has the advantage of being easy to work with on site and not requiring a metal shop that needs a mechanic with a good bit of experience in metal fab. I’m not a duct board fan, I’m a tin knocker 3rd generation, so I’m a bit prejudiced about that.
I had one just like that. I ohmed out the limit string which was fine. I noticed that the 2 yellow wire connectors were loose in the molex plug. Tightened them up and all was good no call back.
Here's one. Got sent to a apartment to check out a wall heater that was putting out high carbon monoxide according to the electric company. Got there and opened it up so I could check it out. Found signs of rollout by the burner orifice and upon lighting the heater and turning on I discovered the burner was 99% clogged. Cleaned it out really good so there was no longer any plugged areas and then had roll out across the whole burner constantly. Tried to turn the burner pressure down and it didn't matter what I did I couldn't get the gas pressure to go down at the valve. Wound up replacing the whole heater instead of just the valve. Not fun when you also have to remove a ball of dust bunnies the size of a cantaloupe from the area under the wall heater. That scared me when I pulled all that out from there because that's years worth of fuzz and the tenant hadn't lived there that long.
I despise tenants with a passion. most tenants where i am are very sloppy, basement, closet, or attic so dirty I hesitate even kneeling down much less sitting down by the furnace or boiler. Worst tenants to have are those who are in a co-op (aka assisted living subsidy, welfare, or some sort of wage subsidy program). they will let grime, mold, and animal poop set in on just about any surface imaginable and i always get told the same thing “i’ve been meaning to clean that”...biggest lie constantly told and that’s one told by all manner of client rich or poor.
@@mpurecat4155 for sure. Had a tenant move out and when she moved in the apartment was absolutely spotless. Even the channel the windows slide in to open and close were clean. She hire 2 maids to clean the apartment when she moved out and then started demanding her deposit back. No surprise that the apartment was halfway cleaned and some damage done. Exterior door had been damaged, screens damaged. Windows hadn't been cleaned or the channels cleaned. Moved the refrigerator and it was just cleaned around. This tenant is losing half their deposit
@@jeffreymurdock8366 in terms of tenants I usually understand a bit of leeway with regards to damage to certain things provided it isn’t much damage at all. Especially if it’s been a few years. As an hvac tech, screens i like are the sliding kind or the ones that retract/wind into a really nice slim container on one side of the door. Screen doors though on the other hand are stupid. Bringing anything in the house requires care positioning, holding and manoeuvring as to not damage the screen. As a tech i usually have my backpack of gear, trouble light and paperwork pad, i can’t count the amount of times I’ve caused a slight bit of damaged to a screen door even with being careful. I can’t imagine bringing in groceries or boxes or anything like that on a daily basis across a screen door. Main reason i took off the screen door to my house and replaced it with the retractable one. Though with regards to the window slide part i can see that being missed even by cleaners, not something usually noticed by people nowadays, and as for the fridge i’ll be honest i wouldn’t expect a cleaner to move a fridge out of the way to clean underneath regardless of their strength/ability to do so. even myself i just have a vacuum attachment maybe 1/4 inch or 3/8 thick and it’s long, it’s about 2 inches wide and the hole is on the side, it’s meant to go underneath things like fridges or other low raised furniture
@@mpurecat4155 I agree and usually we do but this was a problem tenant that had been causing problems all the time and costing us a lot of money so we are taking all damages from her deposit. No screen doors just window screens. We do have security gates on the doors and hers was damaged but we aren't putting that on her even though its her damage. We already had plans to replace it with a heavier duty one.
Boards with intermittant and hard limit errors are usually a result of a break in a solder joint (cold solder break). Not easy find visually since they don't burn, just crack around a pin leg. Often caused by thermal expansion/vibration + insufficient solder from the factory. Solder breaks are completely recoverable and only the cost of solder and time. Prohibitive though becuase of warranty/return call risk/time=money.
I had a situation where a low voltage wire harness was loose at the molex connection on the board and the board was a giving a high limit code. Any time you’d move the harness the furnace would operate normal. Changed the board and no issues since. American Standard furnace btw.
Some jumpers on that board are corroded, the blue discoloration is corrosion. It looks like it's caused by the silicone applied over it which is possibly corrosive. You'd need to dig those jumpers out and replace them.
good catch, I missed that! but that's green in color, looks like glue/epoxy over-coating, probably for vibration proofing or moisture sealing. I'd look at the back of the board and see if it's corroded after seeing the front. probably yes if that is corrosion and condemn the board of course
Firstly, your video's are great!! As a Licensed HVAC Contractor here in Connecticut I'll weigh in on your taping door switches. Here we don't have many crawl spaces with foundation vents, we have basements. If Joe Homeowner tapes a door switch and leaves the Blower Door off it will pull the basement into a vacuum. Causing roll-outs on gas, melted fuel pump couplings in oil burners, Carbon Monoxide in the home. So, I'd just ask that you consider your audience. Everyone watching doesn't have your level of training and doesn't know what you and I know. They're just trying to save a buck or maybe just enjoy being self sufficient and doing their own repairs. Anyhow...............Your a big boy fully capable of making your own choices. Best of luck
Those blue ceramic discs almost never fail; they are x1/y2 safety capacitors, and made to take AC line voltage (they're high reliability). That high tolerance +/- 5% resistor bank has generated its share of heat, quite possibly, that's where the error is. The IC appears to be used in a comparator function, if those resistors are off tolerance, the chip will read errant signal/voltage, and most certainly have triggered the default safety position you've encountered.
AMStationEngineer If you rewatch the video he flips the used board over, the area under the resistors near the main chip is discolored. I think you nailed it on the head, Sir. I am always concerned when I see that on any board, if it isn’t failed out already, it will either create intermittent problems or smoke out at 3am Sunday morning. Thanks for participating with your experience, that keeps on our toes. Have a good day, be safe.
+Wet Headed Tin Knocker': Thanks:-D, when they take continuous heat, in identical fashion, I'll betcha that when the board was 'stuffed' - then wave soldered, the PCB assembler/post wave solder tech thought that resistors on a board are supposed to be flush to the board; when in all actuality, 'water soluble component standoffs should have been used/otherwise included. Metal film/metallized resistors seem to "wanna glow red'. The big "peeve', is that we are supposed to be a 'society of recyclers', yet nothing is repairable, it's mostly landfill/lead recycler 'bound'.I'd like a crack at one, just to figure it out. You might just enjoy this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-jGfYdTeHin8.html
i have seen that board run the inducer non-stop like you described many times... if your ever in a pinch and parts are not on hand, you can flick the relays around the inducer motor jack plug to get it to run normally, usually for a limited time since the relay is pitted and will eventually fall back into the stuck closed position. sometimes it doesnt but most customers don't like the unreliability and opt to replace the board. i would guess your fiddling with the wires was fixing it temporarily.
I've run into this many times on this board. I believe the molex pins go bad inside the board and get loose which breaks the circuit. I find you wiggle the molex you can start the furnace up proving the board is faulty
I always keep a huge pile of various furnace control boards laying around from warranty swaps and change-outs. More often than not i'm reflowing cracked solder joints caused by vibration. As long as the problem isn't internal to the MCU, the IC itself or water damaged to hell, most boards are repairable.
@@Spector_NS5_RD Working for a large service company, we do not do repairs that we cannot warranty. Having 50 technicians carrying soldering kits to repair boards is a waste of our time and resources. It just makes more sense to replace a faulty part, rather than try to repair something that was not meant to be repaired. Especially considering the board is a universal single stage HSI control, it is readily available.
I had a similar failure in a similar-vintage Trane furnace just a couple weeks ago. Actually it started in November - I was getting a high limit warning. The high limit switch seemed to be all over the place as far as continuity so I went ahead and replaced it. Then about 3 weeks ago I started having lockouts...my ignition sequence would run normally, except that when I got the relay click which was supposed to open the gas valve, the gas valve didn't open. I reseated the 12 pin connector a couple times, the issue would resolve for a few days, and then the problem would return. It was weird because whenever I shoved my voltmeter probes into the pins for the gas valve, the issue would resolve and I would have voltage. I did put the voltmeter on the gas valve and found that even with the click of the relay, I wasn't getting voltage to the valve. So I figured either a failing board or cold solder connections for those pins on the board. I thought about taking the board out and trying to melt down the solder connections...but I didn't trust myself to make that a lasting repair. So, after this happened 3 or 4 times I bought a replacement board and installed it. No troubles since. Yes, I am a DIYer, so skewer me...but I have significant experience testing and troubleshooting electrical circuits (I am still what you'd probably call a "hobbyist" though.)
Mine is intermittent and I had then same code 4 and checked all the switches and sensors which were good. I changed the board and did not even turn on. Put back old one and worked fine for an hour. When it was inop, I tapped on the board and started working. Apparently The new board required a jumper from R01 to Ro2, so i changed it back in and put the jumper. It now just turns on the main fan, nothing else. I put the old board back in and works for a while then I tap on board and works. Very frustrating as I know the Board is bad but cant get the new one to work. Same company, White-Rodgers unit too!
This is exactly what is happening to me. Error code 4 but the limits rang out with no issue. So frustrating. I could not understand why it was working and then not working, I thought each time I had fixed it, but now I know. I am going to go ahead and change the board.
I’m a homeowner and fix all my own. That switch would be wired past. I haven’t been beat yet. I studied for the hvac test and might take it so I could buy Freon.
A digital multi-meter can occasionally mess you up. In my experience on commercial aircraft I have seen continuity using a digital meter and high resistance using an analog meter. The digital uses less current and responds quicker than an analog meter. Just food for thought.
I agree, but there are low impedence adapters made by Fluke, perhaps by others, that keeps the input impedance low, based on the voltage present. More voltage, more impedance. There are also some digital meters, not many, with a low impedance function. But great point, I've seen tons of Ghost Voltages in heavy industry.
@@jeanjean9343 I remember scoping a wire on the fitz that had some voltage on it, but I knew for a fact was not connected on either sides. Sure enough, every digital fluke we used would read the voltage, but the one analog our team had would read it open infinite, 0V.
Yeah I've had the exact same thing happen to me before, ended up having to go back out to change the limit. Now I just change them if there's any question.
I had the same model, same issue. shot both open limit sensors but still getting 4 flash error code. Replaced control board and it worked at once. The control board is dang hard to find though
Had a tech at my aunts place say she needed a new board, baught a new board because the high limit switch showed continuity right after it would cut off. had four flashes but I pulled it out and let it run out of the hole and it wouldn’t trip so all it that was wrong was the high limit switch. The place needs a return trunk line put in the house was set up for a common return but threat turned out to be a mess.
I have a question if you don't mind. I lived in Texas before retiring to the Philippines. We want to get a part time place back in the states. The place we are looking at has a HEIL system throughout. In Texas had the same but really it was a"made in HELL"unit. What's anyone's opinion on that brand? Thanks.
it’s an icp product. Ive installed icp products for 6 years now and I’m yet to have any call backs on any of the systems. It’s not always the product it’s the installer. Proper system sizing for the house coupled with proper duct sizing and installation practices you’ll have reliable equipment for years to come.
Did the fan shut off when the wire fell off the jumper at 9:45 or was that the switch? Mine runs without the sensor with wires loose not jumpered at blower. All 4 sensors/rollouts have ohm readings when cold. Wire end has burn mark in on clear covering but sensor is clean.
Copper pipe on Natural Gas oxidizes from contact with the gas and throws off flakes of oxidized copper that can plug the gas valve. Yes, there's the dirt trap, the extended and capped piece of black pipe where the copper connected, but there's no sense in taking a chance. I realize you didn't install the pipe, just a general observation. You tape door switches and leave them taped, documenting your negligence should any mishap happen at the residence. The door switch is to keep the unit from running without the door. On most forced air furnaces, an open blower compartment will draw combustion gases in with the air rushing in the removed, or displaced door, that may cause serious harm to the occupants, or worse. Televising that you regularly defeat a safety feature just doesn't seem like a good thing to do. Lawyers would have a field day. A side note, remember that pulling air from an open furnace door might even pull flue gases from a nearby water heater. Not something that should occur beyond the diagnoses and repair. Limit switches. I've talked to techs that were surprised that limit switches can be diagnosed by taking voltage measurements across the limit, or across a group of limits while you narrow down the culprit. Assuming only one limit switch is bad, and that they're all N.C., the open one will show the full, or nearly full, control voltage across it. With limits that exposed, it can make short work of diagnosing a bad limit switch. In any case, good video, nice work.
I had a similar issue with a Trane package unit checked static pressure was good temperature split was good gas pressure was right went to HL switch jumped it worked a few times the. Kinda guessed it was the bored, any tips to determine it's the board quickly rather then testing all things?
I looked at a newer high efficient train gas furnace and it kept flashing open limit or roll out I tested every limit and roll out and they were all closed I said it needed a new board the owner got a train guy over there and he said he got it going without replacing the board do you know what he did
I do not like long copper gas pipe loop. Easy to trip on and damage it. I would prefer black pipe very close to the furnace and a short flexible gas line to connect the black pipe coming out of the furnace.
Trane XB80 f.a.g.heater 4 flashing codes say bad high limit ( same thing as yours ). I checked the HL and rollout switches for continuity all good. Has no hsi glow action, hsi has continuity
I rinse mine with water every light bill except in the winter. Cleaner should not be used on spine and micro coils. I’m not sure what kind of unit you have. A .042” of dirt on your coil can reduce efficiency by 21%. So yes rinse your coil. Watch your service tech to see how he cleans it and do it the same way.
Ever had the main blower work but have to reset switch? Seems to happen on one I've worked on many times. Shows limit switch open in light code.... test them and they're fine...jump... still doesn't work... reach back far enough to push a reset on the main blower....works....🤷
I don’t think you tested that bimetal switch correctly. Those switches are a bimetal snap switch based off heat. They are normally closed or normally open switch and can only be tested with a match or lighter to snap them and measure resistance.
