Troubleshoot the circuit board of the gas furnace

[@PK_Diaspora]

Mister Gray, I just want thank you once again for all your informative videos and share with you what I just finished doing. My furnace was was not working there was no fire on the burners and it was blowing only cold air. At first I thought it was the ignitor, I rules out ignitor because there was a bright orange light glowing near the burners, then I thought it was the gas valve because there was no gas. But after watching your videos and learning how to check voltage to a gas valve I was able figure out there was no voltage going to the gas valve, (I used a cheap voltmeter from Harbor Freight to test the voltage). Since there was no voltage going to the gas valve I guessed the control module must be faulty. I reluctantly ordered a matching control board and I just installed it. And now I have a working furnace thanks to you.

[@grayfurnaceman]

Glad you got it going. GFM

[@steveg5576]

Thanks Gray - these are fantastic videos. I have a Trane 1993 yr that dropped out. A wiggle on the harness to the board fixed it - it clicked on / off so I zip tied the harness to a slightly different position. Works great now ------ but you showed me how I might be able to re solder a terminal if needed. I'll say I got a White Rogers module on Ebay for $30 -- but the zip ties are holding. I had a serious illness a while back - I've to come to YT to figure things out as my budget has been tight. Now my gas pack downstairs is acting up --- so I'm studying and learning. Thanks a lot.

[@bobhartley4790]

Thank you. It's people like you that take the time to post videos that save me $1000s of dollars every year. The tech was going to charge me $600. I spent $4.99 on solder. Oh, people can get a contractor to them at the supply store, buy the part and pay them in the parking lot for their time. Fuck the system!

[@michaelmace924]

Bob Hartley You're not only paying for the parts and labor but also the knowledge the tech has. Sure, you may be able to fix it yourself, if someone told you what the problem is. Unless you know what you're doing, you're just a parts changer. I just had a service call on a heat pump for a customer who saved himself a few bucks replacing his capacitor. But he wired the thing wrong and had to pay me to come fix it and the new problems he made. The total price for the whole job was $750 and I cut him a deal.

[@MrStephenenright]

Bob Hartley i

[@PK_Diaspora]

Thank you for an excellent video. I have watched several of your videos and in each one of them you explained very clearly by using very basic terminologies. Thank you once again, sir.

[@grayfurnaceman]

Welcome GFM

[@PK_Diaspora]

Just want to add one more thing, I never ever knew how to test/check voltage or had any idea how a furnace works. So, this comment could be a motivation for those who are afraid to fix things at home.

[@ajmckay2]

Great video! Just earlier today I attempted the repair of my furnace board which had 1 resistor that had obviously cooked itself too much and the solder was burned. Ultimately that didn't work so I replaced the board but as it happens I was looking for similar issues to what you pointed out. I should also say that since it's 35 degrees out I was hoping I could at least get the heat working but I wouldn't have trusted the repaired board long term - only to confirm my diagnosis and until a replacement board arrived.

[@stepheneubanks7374]

Thanks for your video. Looked at the back of my circuit board an found melted solder to one relay. Repaired that and fixed problem.

[@grayfurnaceman]

Glad you got it going. GFM

[@geobeard3804]

Hello from MST. thanks for the video. Great stuff

[@grayfurnaceman]

Thanks for the info. The videos are great. I have linked them in the video. GFM

[@Nichlo88]

Gray your videos have been a god send as newish service tech. Thanks for all your work its really awsome man thanks!

[@grayfurnaceman]

Life is good when you win. GFM

[@chrisscott1547]

The relays are a very common fail item, and easy to replace. I've seen them get intermittent too.

[@porter5976]

My gas furnace/ac quit working. It turned out the fan wasn't working. I ordered a board from ebay and it fixed the problem. I checked the board and one of the coil inputs for the fan had a cold solder joint. I guess it had gotten hot. I checked the 3 big relays with DC input and they all clicked so I knew they were good. I repaired the cold solder joint along with a couple of loose resistors. I haven't yet but I plan to reinstall the old board. If it is good and stays good for a while, I'll have a spare board or I'll sell the newer one on ebay.

[@glasser2819]

@@porter5976 keep your spare board handy for a cold winter or a hot summer day, save your time

[@sheridenmon3519]

THANK YOU SO MUCH FOR YOUR PROMPT ADVICE. REALLY APPRECIATE & ENJOY YOUR FEEDBACK.

[@erice.5844]

In addition to my message below from earlier today, .... had went back and checked the igniter plug, AC reading from the wire coming from the control board.... inserted leads and turned power on, 0 anything, when jumped R-W and running long enough before blower shut off.10 seconds. couple tries.. So the power relay/ larger one on board maybe effects if the igniter gets any current at all ? Was going to inspect the thermostat part, and igniter part for discoloration, but no voltage coming from the board, passed on it for now. again your thought on appreciated knowing this. Thx Eric MN

[@grayfurnaceman]

The ignitor only gets power for from 15 seconds to 45 seconds depending on model. It gets power after the pressure switch proves for aforesaid time period then shuts down. The first thing I would check is resistance of the ignitor. Isolate it and check. Should be 13 to 18 ohms for stick ignitor or about 150 for the one that looks like a wavy element. GFM

[@erice.5844]

just removed Ignitor, and cleaned it up a bit. realized I used too high of a ohm setting .. used lowest one and have a reading.. 20, and sometimes fluxates 40-70.. do not zero or one as I thought at first! will look at thermostat rod and clean it, but back to the board not sending voltage to the ignitor? will have to test again to see if I can run it longer to see for sure if the board is not sending any juice to the ignitor... Any other things I should check.. to see if good, faulty.. If ordering parts would be nice to get everything in one order, since I will be waiting on the ship time. Thx Eric

[@erice.5844]

Thx for reply.. Gray.. :) > Switches & Relay part that smoldered.. T9AV1D12-22 Is part number last larger relay on left of board.. switches between 30A, and 20A... so think may be fan relay.. runs in couple speeds. Also did try to trouble shoot thermostat only and does come on temporarily with new batteries 10-20 minutes before going blank again. as mentioned code green and red are solid on which indicates normal, even with the part frying on the board? PS the J tube as mentioned was clogged, darkend in an upper spot before the water pump.. and broke in that spat, wether me currently looking at it or, last spring?? Do you think it may be a ok idea to buy part, sodder and if something goes wrong, get a new board.. hate to pay allot of money first to see the same thing happen? may get a new thermostat for precaution as well. n check voltage outgoing and ingoing to the board? may need to look up how to do the testing of that.. appreciate your feedback on it. Thx Eric

[@grayfurnaceman]

Here is what I would try. Jumper R to W at the control board. If the furnace runs and the fan motor runs, there is probably no problem with the board. You can also jumper R to G. The fan should come on. If all that happens normally, replace the thermostat. GFM

[@bobbyw.4985]

those who are afraid, actually watch the repair guy, you will learn so much, and they can't tell you you can't watch and be involved.

[@electriciandallastx9182]

Thanks for the ideas you have provided here.

[@jerrypeal653]

Lots of diodes and easy to check . I’ve found a bad zener before on mine . Only thing you can’t replace is the microchip processor U1 U 2 possible but for the price it’s not worth it .

[@grayfurnaceman]

New motors seldom burn out if they are wired right. You need to check amp draw of the new motor when its running. Should not exceed rated amperage. Check the back side of the board to see if any traces are burnt. Hope this helps. GFM

[@erice.5844]

will try... one thing forgot to mention that I fixed with white viniger... corroded bottom of one bateery connector.. cleaned up nice... and a fine file before that.. but appreciate advice.. But stil have to replace power relay!! on the board.. in oppose to replacing.. full board for 200.00 ... yes!.. but doin break jobs, exhaust.. n other car stuff... is not the toughist thing in the world.. Thx Eric..

[@erice.5844]

GFM researched how the power relays works in general and problems do arraise with them burning coils/connection tips... . Also put in a new Thermostat, similiar to old one, went in smooth, fired up furnace, gas, and large circulation blower. ?? serious on this question... the larger power relay that has a hole burnt through it? part T9AV1D12-22 What is your opinion on if I absolutely need to replace the part/board.. and what you may know what it opperates? Being the furnace seems to run ok and cycles normal! Only thing I can think is if it regulates a 2 speed option with the large or small blower fan? I know years past it des have a low and high audible modes. Know I am overloading you some, but this is the main issue I am looking for good advice on .. :) Appreciate the help. Eric

[@grayfurnaceman]

Whether you can buy one is dependent on manufacturer and age. I don't know if there are any federal regs in Canada. Repairs are not recommended by the manufacturer. I give vids on limited repairs to solder joints on some parts of the board that should be done only by someone with the skill and confidence to work with circuit boards. When a board is replaced, it should be tested for all safety dropouts to assure it will not allow the furnace to operate unsafely. Hope this helps. GFM

[@canuck-guy2384]

I have a coleman counterflow gas furnace model DGAD060CDL. There's this tiny black button switch on the mother board in the upper left hand corner that reads Last Error. What does that do? Just curious. I'm having intermittent furnace issues right now, but I don't think it's the board.

[@grayfurnaceman]

If you press the button, it will give the last error code listed. GFM

[@canuck-guy2384]

Thanks. I may have to replace my board. I'm having it checked tomorrow. I'm afraid to touch it if it's not the issue. Too many other things that may be the cause of my intermittent issues.

[@erice.5844]

Did perform the jumpers suggested. R-W, and R-G.. only wires hardwored to the board. large blower/fan on R-G came on, and dmall blower came on for R-W, though tried a second time after turning gas on and the green light started to blink, (code pressure switch open fault? That has to do with the burnt out power replay? I did leave the j-tube disconnected as was going to repair it in the lower compartment.. But the furnace did not kick on when the small blower motor was running, no gas first test and 2nd test green blinking led for pressure switch open...fault. again the power relay part on board is burned up slightly. any ideas to isolate. looked up a couple things to look at for what the code relates to directly. Thx Eric

[@grayfurnaceman]

First, remount the tube and be sure the trap is filled with water. Sometimes the pressure switch will not close if the trap is not filled. If no luck, look for blockages in the vent. GFM

[@erice.5844]

@@grayfurnaceman ok will do..

[@mark.r8900]

thank you Gray for all your help. if i unplugged the inducer motor and does not get 120vac coming out of the IFC, then is it safe to say that the IFC is defective. all pressure switches are open when measured with meter. Also, i have a two stage gas valve but why are there 3 pressure switches? thanks.

[@grayfurnaceman]

If the furnace is calling for heat, and has not shut down on safety, there should be power to the inducer. You need to look at the control board diagnostic lights to be sure. If the unit does not have lights, and if it is a York from the 1990s, it may not, the 3 pressure switches are necessary to check for all problems with draft. GFM

[@engrhammad]

Nice video. My Vulcan 550D furnace fuse keep on blowing soon after I start the furnace. What might be the reason?

[@grayfurnaceman]

Is it a low voltage fuse or high voltage? GFM

[@engrhammad]

@@grayfurnaceman how can I check whether it is low voltage or high voltage? It is the bottom one which is blowing. Top one is fine

[@grayfurnaceman]

@@engrhammad Send me a pic. Send to [e-mail] GFM

[@dirkcan7]

I have a similar board except there are jumpers for the fan. I think the fan relay has failed if i remove the on jumpers on the board should the fan still engage ? Thank you for all your videos they are a wealth of information.

[@grayfurnaceman]

If you have power in but no power out of transformer, the transformer has failed or a fuse has blown. In either case, you may have a short in the low voltage outside the unit. You need to find the short or the new one will fail. Hope this helps. GFM

[@erice.5844]

Appreciate info.. part fail! definitely thought.. Should I replace.. n resoder (after removel ) a new 6.00 power relay? ? as feel like I woild be able to.. but would like to test).... will try the jumping options to check fan! first.. thermostat will just assume I will get another one. Let me know if a sodder job, as a test.. may be ok.. (new power relay part) ... before buying a new board.? as leary to install a new board before making sure nothing will fry it again! Appreciate the continued advice. ! ! Home owner DIY'er (within my means..) Eric MN

[@daflyyondawall]

The fan can kick on with no problems if switch on manually. The fuse always blows as soon as a signal is sent to compressor. Also I can get both fan and compressor to run if i jump the control board. Would that short be between the thermostat and control board or between board and compressor? Or am I looking past the board itself being bad?

[@erice.5844]

Nice one Gary... just seen one of the black blocks on my board had burnt corner to it? via a blank screen on my thermostat. ?? fuse good, fan initiated, red/green led on board.. meaning good board on after shutting power off, n breaker did not trip.. so think something like the black cube, will see what it is indicates getting a new board.. even though indicator led's say board is good! .. 13 year old Tappan high efficientcy furnace. w honeywell 7 day programmable thermostat, 4 wired.. mmm lotta stuff to check on thses babbies..

[@erice.5844]

OK reinstalling jtube worked for blinking green code. so no codes currently. Though jumping R-W starts the gas compartment small blower, and with gas on... for 30 seconds tried couple times, and no start up. Assuming the fried Power relay is preventing it. (Did not have the Thermostat connected as well). And again jumping R-G does start up the large circulation blower. your thought. Thx Eric

[@grayfurnaceman]

Forget the relay. If gas comes on, but does not light, check the hot surface ignitor. If it does not glow, it is probably failed. GFM

[@elip1743]

hi, gray so i have a furnace that i replaces the blower motor because it smelled brunt and stop working. the board LED's were flashing slow saying everything is ok, so after i replace it still didnt work i TAPED the relays and it turnd on but after a day i started smelling brunt again and over heat the motor so now have to get another one and maybe a new board. Any ideas what it could be? thanks for your advice

[@glasser2819]

that points to the run cap being bad. Normaly you replace those with the motor as a match. Bad cap causes high current that overates everything...

[@mbarizia]

Hi, thank you for the share, on the main relay i have COM & NO which wire should go to NO? the brown that comes directly from the power supply to the HVAC? please help i forgot how the things were fitted in!

[@erice.5844]

Just a note.. as no picture, the part... power relay and number I posted, is literally burned and smoked.. so no guessing on that part of the board needs to be replaced. or new board. how it happend? clogged j-tube where the water drains in bottom compartment, or me switching the breaker possibly wwhile power was on to the furnace. Appreciate the advice to determine the thermostat. it does come on with fresh batteries.. and is 4 wired at the wall. Thx Eric

[@grayfurnaceman]

Neither the plugged drain or switching off the furnace can damage the relay. The only things that would cause that are overload from a shorted motor, the relay simply failing or the coil burning out. GFM

[@limplin7]

Can you please tell me what is the model of "C3" from board 50a65-475...I believe it is capacitor. Mine is exploded so I cant recognize or read it.

[@amtpdb1]

How would you find which connectors and which relays handle turning on the gas valve? I replaced one board and the only thing that did not happen was the gas valve would not turn on? Thanks I just wanted to check the relay for myself to trace it back.

[@grayfurnaceman]

+amtpdb1 Beats me. You can try following the traces on the board that connect to the gas valve. You might also be sure the hot surface ignitor comes on. GFM

[@amtpdb1]

+grayfurnaceman Thanks

[@amtpdb1]

+grayfurnaceman The hot ignitor works as it glows nice and write. The gas just did not open to heat.I replaced the board and all works. I just wanted to find the issue with the board but before I closed the unit I forgot to note the terminal to trace it back. Thanks for the video.

[@Veritech05]

Thank You, I traced the short to the unit outside. Do you think is the relay?

[@grayfurnaceman]

Can you tell me what make and model. GFM

[@montybridgewater]

Grayfurnaceman - I have no power coming to my circuit board. I can push down the contactor and make the compressor kick on and it is working fine (as long as I manually hold down the contact)-- the LED lights are not lit at all which designates no power to the board. I have checked all connections and they seem to be connected. Any suggestions?

[@grayfurnaceman]

Look for a fuse on the board. Also check all breakers and fuses to the indoor unit. Hope this helps. GFM

[@maktro257]

Great video. I have a strange issue and was hoping for some input. I have an Armstrong Garage unit that powers on the fan and exhaust when plugged in and the control board green LED blinks for the first seconds (1 min?) ...then when you would expect the ignitors to start "zapping", they dont, but the control board LED (Green) goes very dim and rapidly blinks a few times and then goes dark, as if the control board shuts down. The fans continue, but nothing else happens after. If i unplug, the above process happens again and again...the ignition sequence worked before, now that doesnt even work. I checked power to the gas valve when the ignition units were working and there was no power to the gas valve, however there was power coming out of the 24v trans.(the output of the 24v goes into the board and comes back out to the gas valve so my guess is it is being lost in the board somewhere). Any input?

[@grayfurnaceman]

Maksim Trofimovich It could be one of 2 problems. The gas valve could be shorting, which may be causing the dimming. Removal of the wires from the gas valve may tell if the light does not dim. The other is the board is not passing power on a trial for ignition. With the wires on the valve, do a trial for ignition. Put voltmeter probes on the valve wires. When the trial starts, anything other than 24v or higher means the board is not passing power. These steps should be done in the sequence above. Hope this helps. GFM

[@maktro257]

grayfurnaceman thanks for the reply. When i was troubleshooting this board, i ran it with and without the gas valve wires connected. Same result, dimming led, then nothing. Before it started dimming on me it was just an issue with no voltage to the valve., it would run the ignition process, but there was never voltage to the gas valve. I thought it was a 24 v trans issue so i replace that, but same issue. It seems like the 24v is getting lost in side the board some where. If a board is not passing the 24v, does that usually mean bad board? I plan to look at it again and follow the trails, but i feel like its going to lead to a chip or something, which is basically a dead end. But then again, now it is dimming the LED and shutting down the board completely so not sure where to go from this point. Side note: i did test the gas valve via the hot wire process using jumpers from the 24v source and it clicked open/closed, so from what i understand, the valve should be ok. Thanks.

[@garycrosby8984]

grayfurnaceman Hello Gray furnace guy...thank you in advance for your help. I have a rheem electric furnace / air exchanger with a cooling unit mounted outside. The electric furnace / air exchanger is ion the attic I live in Florida. It all has been working jusat fine then the then the other day all of a sudden the fuse blew on the board , I replaced It then the transformer started cycling on and off and started smoking...I shut down the power and so I got a new one, I put in a new fuse and the new transformer and it worked for a about five minute then the transformer started to cycle and heat up again. This happens on either heat or cool I checked both sides out... it (the transformer) however does not heat up when just the fan only is running it runs just fine. Do you think its the control board. I do not believe its the thermostat as that really is truly just a switch. HELP its hot down here!!! LOL...

[@erice.5844]

Sorry, forgot to mention that R-W jump (I keep the jumper on it for 30 seconds), only turned the gas section blower on, no frst click for gas to come on, or of course igniter. Tried again ... jumped R-W a couple times by touching conections for a second, couple times and blower comes on for a short time, then shuts off.. No smell of gas, and no clicking, just the blower powering up.. assuming with no gas being sent that is normal, (again no red/green codes and did have gas emergency valve open prior) going to try to dig little, .... appreciate your wealth of guidance! Eric

[@intelin123]

i got a goodman furnace . i got 120 going in and out of the board going to the xformer but no 24v coming out of the xformer. fuse is good. fuse has continuity. i put in a 5 amp fuse and it blew it. but it does not blow the 3 amp fuse it came with . the status light does not light up.

[@grayfurnaceman]

I think you are missing something in your testing. Your fuse is probably blown. You have a short in the low voltage, probably a wire touching the chassis. GFM

[@Billstang]

I have a Honeywell board ST9103A controlling my AC and oil furnace. It looks very similar to the one you are showing in this video. I replaced the board because it had a burned connection on the relay. Everything is wired identically to the old board, but it won't come on. There is an electrical box with a switch and a line comes from the box and goes to the board prong labelled 120 VAC (black wire). I am trying to figure out if this is supposed to be energized and if this is where the board gets its power, or if the board energizes this line to the box and then to the humidifier and or electronic air cleaner (both have lines coming out of the electrical box.) Any assistance would be appreciated!

[@grayfurnaceman]

That is the line that powers the board. GFM

[@Billstang]

Ok, perfect. I wonder if you could answer another question for me. I have a carrier AC (and a beckett oil burner). When the thermostat calls for cooling the outdoor fan and compressor comes on, but the main indoor circulator fan stays off. I replaced the board, it had burned relay solder joint. But with the new board, the circulator fan still won't come on. The fan works fine when I jump to the G wire from the red. Is my thermostat supposed to energize both the yellow and the green for ac or just the yellow and then the board energizes the blower motor? I am stumped because I can't figure out why the indoor fan won't come one. I have a nest thermostat which seems to be having trouble getting power on a 4 wire system lacking a common. Any insight would be appreciated.

[@grayfurnaceman]

You have a thermostat problem. The thermostat should energize both Y and G in cooling. You will probably need a common wire to make this work. GFM

[@Billstang]

Perfect, I called Nest and they had me run some diagnostics by switching wires around. They said the Nest was indeed bad and they agreed to send me a new thermostat. It is true my Nest doesn't like not having a common wire, it charges when the unit runs but will die if I don't run it often enough. I guess I need an electrician to pull a common wire through the wall? Thanks for all your amazing site. I have learned so much watching your videos. Thank you, Mr. Grayfurnaceman!

[@grayfurnaceman]

I will be uploading a video on how to pull the wire through. The question is when I will get it done. GFM

[@billwhipple1260]

Hi Folks, I have a Goodman GDT115-5B furnace. It will light and run, but is burning out the fuse. How do I troubleshoot, and fix? Thank you. BW

[@jettramel]

Not the same board by any means, but I hope this will help me fix my Kenmore Air Condtioner, a relay for the compressor is stuck, so it runs when you just plug the cord in. I can't find these boards.

[@erice.5844]

update, checked resistance, 200ohm mode, cheap checker.. did it a few times. and jumps at first then goes to 1.. so, know the board power relay needs changing, or new board, this part.. j-tube modified hard tube to not get the green light blinking code! what next? mmmmm turning into a few parts here.. but glad I have some good guidance.! first time home owner here. Where to start.. or what else to check.. :) Thermostat may replace as well for good measure! Thx Eric

[@bradhn3832]

Hey gray , I just installed a new packaged gas and electric Payne. Tried to fire it up but no power . Traced power to the transformer but no 24 coming out. Being brand new, do you think it's still the transformer or am I missing something.

[@3beltwesty]

The replacement board that fits my 1985 carrier furnaces has its timing capacitor fail that defines the time the furnace runs after the gas is turned off. It is the largest capacitor on the board and I just replace them.

[@grayfurnaceman]

3beltwesty Go for it if it works. GFM

[@grayfurnaceman]

Look for a short to chassis in the Y or G circuit. Commonly this would be a screw pinching a wire or insulation scraped off the wire. Hope this helps. GFM

[@heikotimaile1752]

Thanks for your videos on my control board it takes a 5 amp fuse I used a 10 amp fuse to get things going knowing I was going to switch it back to a 5 amp. Well my dog chewed the wires at the ac unit outside my wife got hot and turned on the ac. Well it short and in stead of the fuse popping something else burned out. My question is could it be the whole control board that's fried or something else? Hope this is enough to go off on and my control board is a Honeywell ST9120U anything will help. Thanks

[@grayfurnaceman]

+heikoti maile It probably took out the transformer. The board should be ok. GFM

[@joesmania]

Mine is throwing a code for "reversed polarity". All on-line sources say either a short in the wire or the board is spent. Any input?

[@grayfurnaceman]

Be sure all power wires are tight and white to white and black to black and the ground is hooked up. Sometimes, there can be feedbacks from other loads. You could try using another breaker in the panel. You are working with lethal voltage here, so do not do it if you are not confident. Hope this helps. GFM

[@joesmania]

Thanks much! A big help, yes it was!

[@jettramel]

Not the same board by any means, but I hope this will help me fix my Kenmore Air Conditioner, a relay for the compressor is stuck, so it runs when you just plug the cord in. I can't find these boards and need to fix this AC, can't afford a new one.

[@CognitiveDisonance]

Non-field serviceable part means non-field serviceable part. Repairing any lose or cold solder joints is perfectly fine, but If those resistors get hot enough to melt the solder that hold them in place, then you have a bigger problem than a couple of burned parts. While it is certainly possible for an engineering technician to troubleshoot and repair printed circuit boards to the component-level in an electronics lab, with the proper equipment, schematics, and spare parts, there would still be the need to perform reliability and safety testing. Simply plugging it in to see if it works after a makeshift repair effort would fall far short of full-function testing. Just because the furnace fires, does not mean its safe.

[@rybaluc]

Well, it depends. Siemens LMU64 control unit(used by many mainstream furnaces) had a manufacture problems when they used bad electrolytic capacitors during a manufacture.So 1-2 years and furnace cannot start even if ionization probe is ok, but circuit in control unit which evaluates discrete analog values was bad. This unit cost over 5000kc (200$) here and manufactuers change unit for unit only. Work,reprogramming of values for specific furnace,installation not included. And this price is without additional modules on lpc for solar heating or home automation.Just small furnace configuration. If it cost so much money you will really consider repair on your own. If you do a bad job what worse could happen? System is designed to be safe even if unit fail completely unlike those ancient furnaces presented here.

[@obsoleteprofessor2034]

Concerning capacitors check out this Wikipedia article: en.wikipedia.org/wiki/Capacitor_plague There is a guy on YT by the name of Louis Rossmann who is doing component level repair on computer motherboards. His techniques may give you some info you may need.

[@rybaluc]

obsolete professor Those failures are attributed to units made after 2010 up to present. I suspect a warranty engineering here. All furnaces using Siemens LMU64:( However there is no chance to buy anyhing different. Especially if you have low temp central heating and well insulated house with low and unstable heat loss. Geminox furnaces can regulate flame 1%-100% with 1% granularity.

[@obsoleteprofessor2034]

Thank you

[@otonielflores6302]

CognitiveDisonance

[@reedkwize1]

Before this the igniter would glow and then the fan would come on and the igniter would go out. There is a harness with a wire going to the limits and when I push on it ( to make sure it’s seated) the blower would me on. Also I tested the limits and they read continuity while the furnace was off.

[@rasmussen667]

can you give us a video on the tips and tricks of soldering a circut board have a firm grip on brazing not much luck with the iron always a big puddle or just no bond

[@grayfurnaceman]

I have just added a vid on soldering circuit boards. I will be adding more about soldering and brazing as I get time.

[@0914mregd]

hello grayfurnaceman can you tell me where can i get one circuit board just like the one you were showing in this video?

[@grayfurnaceman]

There are 2 choices here. One, you can get the factory part from the manufacturer. Two, Some control boards can be replaced by general replacement boards Made by Honeywell or White Rodgers. They have crossover charts to be sure the new boards works normally. GFM

[@reedkwize1]

So if the blower motor comes on right away and the limit switch is closed can that be an indicator of a bad circuit board?

[@grayfurnaceman]

I would be looking for other limits. There could be as many as 4 including rollouts. GFM

[@RitchieVee]

I need your help, my Coleman Heating and Cooling system is acting up. When heating my house the furnace only heats up one degree at a time. ie. My thermostat is programed for 66, I will manually put thermostat at 67. The heater will turn on and heat up to 67 then the heat will turn off and the unit will continue to blow with cold air. The code LED reads Limit Switch open/open fuse. What can I do?

[@grayfurnaceman]

Look for plugged filter or dirty blower wheel. Also be sure all vents are open. If it is a mobile home double wide, check the crossover under the house. It could be smashed by animals. Let me know how you do. GFM

[@69Dobber]

Mr. Grayfurnaceman my problem is that I have no low voltage going to my A/C unit outside (the compressor). I have power to my thermostat and low voltage to my mother board from the thermostat but non relayed to the compressor while the thermostat is set to cool. Do I simply need a new motherboard?

[@grayfurnaceman]

Snazzy Architecture If you mean the motherboard of the furnace, I would do more tests before condeming it. You should have 24 volts between the Yellow wire and common at the furnace motherboard. If power is there, check at the outdoor unit. No power at the outdoor unit and power at the output of the board, then the problem is between the board and the unit. Hope this helps. GFM

[@robertarchuletta2498]

I have a similar board. A 103085. The exhaust pressure switch had a problem. but after smacking it a few times it resolved the issue. I reset the board. there are no error codes now but it won't even attempt to turn on with a call for heat.

[@grayfurnaceman]

Smacking the pressure switch does not resolve the issue. Are you sure you have no error codes? This doesn't sound right. GFM

[@robertarchuletta2498]

@@grayfurnaceman Thank you for getting back with me. I was really desperate. The problem now seems to be my thermostat. I was getting 6 vac between R&W. I thought it was insignificant. But when I jumpered it, the furnace tried to start. Hopefully everything will be ok once I replace the thermostat.

[@grayfurnaceman]

@@robertarchuletta2498 Very interesting. GFM

[@robertarchuletta2498]

@@grayfurnaceman I think I replied in the wrong place. So the pressure (vacuum) switch is working properly now. The control board has been cleared of all error codes. The problem afterwards was in the thermostat. With the thermostat switch closed, I still had 6 volts on the terminals. The anticipater was burnt. Probably as a result of a short I had in the thermostat wires a couple of years ago. The thermostat was fried. I replaced the t stat and everything has been working good.

[@grayfurnaceman]

@@robertarchuletta2498 Glad you got it going. GFM

[@juliangomez660]

Do you guys know if the circuit board needs to store energy ?

[@grayfurnaceman]

I would start at the contactor in the outdoor unit. Disconnect and test. Continue until overdraw stops. GFM

[@grayfurnaceman]

All I can tell you is the traces on the board that go from the terminals for the fan should lead to the relay. Hope this helps. GFM

[@williammchugh4361]

My furnace stopped working last week- code closed pressure switch. Replaced both it and a cranky old inducer fan (which needed replacing anyway) but still nothing. Found No 120v from board terminals to the inducer. Ran 120v manually to inducer from outlet and ran fan. started furnace with one wire disconnected from pressure switch, then reconnected the wire. Furnace started and fired up. Now I'm wondering if it's a bad solder joint, bad relay or something else. Anyone know how to best test the relay in the board? Also, do the 2 wires going to the pressure switch have to be in specific slots? the 2 wires aren't marked differently.

[@grayfurnaceman]

If the inducer cam on when you removed the wire from the pressure switch, the pressure was closed. Generally, its pretty hard to miswire a pressure switch if it is a 2 wire. I don't think you have a relay problem. GFM

[@jimmylopez665]

need you assist. I have a board not sending signal to valve , sequence ok but no reading on valve ... relay?

[@grayfurnaceman]

If the HSI comes on, and the burners don't, and there is no power to the gas valve during the trial for ignition, you either have board failure or the connecting wires do not make contact. GFM

[@nykid8849]

i got in problem today working on ptac unit which had problem with the board the transformer smoked on board and unit never came on adter how can i check with the solder is good or not in the back please or the borad its self it not a furnace unit help.

[@grayfurnaceman]

I did a video on solder joints: kzbin.info/www/bejne/ZmmoZ2p9nMiljLc Hope it helps. GFM

[@1242chisox]

I'm starting school soon for hvac. I've seen on my board, heat, cool, M1 & M2. Is M1 & M2 medium speeds?

[@grayfurnaceman]

+1242chisox Not usually. What brand and model? GFM

[@1242chisox]

grayfurnaceman rheem, I was starting to think maybe it was a dummy terminal, like some boards have the park terminals

[@alexnguyen8025]

Hello Grayfurnaceman ! love your videos, i learn a lot of from your videos. I have a question about the LED. What purpose of LED on a solid state board for a residential gas furnace is ?

[@grayfurnaceman]

In most furnaces made in the last 30 years, the light is used to determine what error code caused the furnace to lock out. It also tells you if there is power to the furnace and if it is calling for heat. There should be a key to the codes on one of the furnaces covers or on the control board. GFM

[@alexnguyen8025]

@@grayfurnaceman Thank you very much Sir. 👍👍👍👍

[@Jeff_S...]

Great video, as always. On the 'heat and 'cool' terminals, are those for the selected fan speeds? I'm also curious what is above and below that bank of neutrals. I have all of the high voltage down, but some of the low voltage stuff can be a real rats nest.

[@grayfurnaceman]

They are for the fan speeds. Those are for Hsi, flame rod and inducer. Hope this helps. GFM

[@PBS-nm1uu]

how do you know which relay controls what ???

[@picklerix6162]

I replaced one of these boards about five years ago and it looked like it was not detecting the flame sensor voltage for some reason. It looked like some of the traces on the back of the board were burned.

[@grayfurnaceman]

Usually, the burn marks are from a high power resistor. That is usually not where the failure is unless the trace has been "haloed". GFM

[@Veritech05]

Outdoor unit disconnected and the short stop. What can be wrong with the outdoor unit?

[@bobhartley4790]

Everyone subscribe and like rigs video....he is saving honest people money. That's got to be worth a click on your mouse.

[@arnoldnavarro21]

hey furnace man, i ran into a problem at a call i had.... the condenssor wasnt getting 24 volts to the contactor, the wires were good, and so was the transformer but we couldnt find out why it wasnt getting 24 volts... we think it was the control board??? any suggestions?

[@grayfurnaceman]

If you mean the IFC, It is not in the control circuit for the air conditioner. If there is a board in the A/C, 24 in, no 24 out, pressure switch or board. Hope this helps. GFM

[@AlchemistLair]

I have a problem with my furnace in which it ignites, for just a couple of seconds and then shuts off. It is not the Flame Sensor as I have cleaned it (1000 grit sandpaper) and even replaced it once but still does the same thing. I get no codes from the status light. Eventually, after several shutdowns, it will run as normal. This continuous cycling of the igniter is causing it to burn out at a rapid pace (replaced three times)!! I am leaning toward replacing the board. Any thoughts?

[@chriskulp8906]

I am having a similar issue. Did some extensive troubleshooting testing the valve and sensors. I believe it is a bad controls board with bad relay that is occasionally ‘failing’ and shutting down the valve (intermittently dropping the 24v) unintentionally. Going to try a new board but I’ve tested everything else.

[@patrickjordan8373]

Ten years later and I'm wondering if you two have resolved the mystery. The valve does exactly what you said, unless it chatters like the teeth of that demon in Hell Raiser. If you ignore it for an hour then try a hard restart it can run for an hour with no problem. My concern is that the vendors who ship single valves to the end user put them in a box the size of a VW with a single air pillow inside (the Amazon method) so that the delicate device is pre-destroyed before it gets to the destination. Then you couple in: Flame Sensor (even an a 3wire pilot), inducer dropout that could affect the pressure switch in microbursts short enought to miss but long enough to mess up proven flame, a bad valve (almost a given but then NONE OF THEM WORK thus suggesting there is a problem somewhere else that ultimately ends up implicating the valve), INTERMITTANT SHORTS, and then faulty reed valves that make contact but don't let the full AMPERAGE through. If they made these device any more complicated they wouldn't work... ...wait.... they don't work now...

[@freon500]

Thank you Gray, thank very much for the video. These days many manufacturers are trying to cash in on the money they didn't make up front by charging a lot of money for their circuit boards. It's gotten so bad that many customers hate service guys because of the high cost of components. Sometime customers end up having to pay 2 to 3 hundred for these things and is scares them, perhaps with good reason. What makes it even worse for us is that sometimes when we put in a brand new board it burns out in a few days or even right away. So what do you do when this happens? We try to replace it by talking to the vender and explaining what happened and maybe he will replace it with another one, maybe because a lot of manufacturers have shortened the warranty period on these things from a year to three months and often when you buy the board your vender has had it sitting on the shelf for a while and for him to have it replaced is not automatic and can be a problem. It has become tricky to stock these items in my van. So being able to make a simple and safe repair becomes a great triumph. That is why I am very happy about this video in that at least it shows us another way we can be of better service to our customers.

[@grayfurnaceman]

Sometimes us techs are afraid of these parts because the manufacturer says not to repair it. When we had relays etc, that we could replace, it was much cheaper. When these things first came out, I thought: oh man, if this thing doesn't work because of a burned wire or relay contacts, we have to replace the whole thing! Then for any given model of furnace we mostly had to have 4 to 5 different boards. There are general replacement boards that helps some, but still the cost is high. When I saw things like the traces burned on the inducer relay in a late call on a cold night, I just said I am not leaving this guy with no heat tonight over this small failure. So I started repairing them. I never mess with anything in the flame safety and always check the unit for all safety shutdowns. Thanks for the thoughts. GFM

[@allenletizia321]

How do I get right board fit furnace ? Can I just go buy a board or do I need get 1 fits that model ? I never heard Winchester .

[@grayfurnaceman]

There are 2 ways. You may contact a HVAC dealer to get a factory part. There are general replacement boards that are made by Robertshaw, White Rodgers or Honeywell. You will have to match your make and model with the board and there will be wiring issues. Not for the neophyte. GFM

[@allenletizia321]

ok thank you

[@grayfurnaceman]

Thx. GFM

[@jilljohnson1243]

Thanks for this. My 95 Trane was blowing cold air today, and code was "System lockout (no flame)/check line polarity. When I reset it (power off and on), it repeated. Repairman reset it (powered off with thermostat), and it started. Because it was inconsistent, he checked the motherboard...said that the earthquakes we get can cause power surges that damage the boards. Indeed, a short while later, he showed me a brown spot on the case, and black spot on the green side of the board. Is this reasonable? I ask because within the black spot on green side, the green is missing in chunks, but looks scraped off..straight lines. Thanks in advance.

[@grayfurnaceman]

I can't say if the board is bad. The brown spot may be normal. Some of the boards use large resistors normally create small burn spots on the board. The resistor is usually white ceramic. GFM

[@jilljohnson1243]

Thanks. Wish I knew how to post a pic to this format. : ) The burn is on the green side. On the flip side are some small green resistors. 1/2" long, group of 4. I appreciated your common sense video. Helped me to understand it a bit!

[@grayfurnaceman]

Send to [e-mail] GFM

[@HolyElkGaming]

appreciate your videos, thanks!

[@grayfurnaceman]

Welcome GFM

[@grayfurnaceman]

Shorted coil on the contactor, if there is a circuit board, a short there. I dont know the manufacturer so I dont know what else it could be. GFM

[@daflyyondawall]

The fuse on my board blows as soon as the thermostat calls for cool. What could be the problem?

[@YourBuddyRob]

Those three blue capacitors have been known to go bad in many devices. (I've replaced them in two of my LG computer monitors.) Have you ever replaced them and brought a control board back to life? I'm going to give it a try.

[@grayfurnaceman]

I have not have one fail. GFM

[@grayfurnaceman]

I need to know what furnace you have. Give me make model and approx age. GFM

[@robertarchuletta2498]

So it's a Dukane. The control board is a 103085-03

[@robertarchuletta2498]

I installed a new thermostat and it seems to be working fine. Thank you so much for your help! God Bless!

[@brendafluellen2280]

Why does my 3 amp fuse keep shorting out? It only happens when I switch my thermostat to heat. My blinking led code is: "Short circuit in secondary voltage 24vac wiring." Does this mean my circuit board might be bad?

[@grayfurnaceman]

+Brenda Fluellen Usually, when the fuse keeps blowing, it is indicating a short in a component or a wire contacting the chassis of the unit. I did 2 videos on finding a low voltage shorts. I have put a link in the video that will take you there. Hope this helps. GFM

[@ranchview3470]

+Brenda Fluellen try checking the diodes , shorted diodes in secondary winding of the stepdown xformer causes fuses to blowup everytime you switch the stat to heat mode.

[@bluntshop713]

You have to re wire from the unit inside to the unit outside I had to do that to mine I went through like 3 boxes of fuses.

[@lazaryanya9407]

Everything about that board is repairable. There is no conformal coating. All components are through hole. None of the component markings are sanded off. The only thing that could make it irreparable is propitiatory parts.

[@grayfurnaceman]

Which the prosessor is. And the software also for the flame safety controls. GFM

[@grayfurnaceman]

Get a pile of fuses and start pulling thermostat wires off the board until it stops. Start with y or cool, then g fan, last, r. GFM

[@erice.5844]

Thx for reply.. do not know if my reply's go right to you? (so reposted last message!) System was powered but not in use..(heat only use during winter) Noticed blank screen on thermostat .what brught me to open up furnace to check things out. Current board when powered shows a solid green and red light, meaning no problem codes, everything ok? funny but true. Just have Heat and the central air fan that activated when trouble shooting the blank screen on the honeywell thermostat. Also looked up bpard for my (Tappan) Nordyne Furnace FG7SC 072D-24B, (92.1 efficient gas forced air)( Parts Circuit Board for G7/M7, sku 920915) 150-200.00 and the burnt out POWER RELAY.. looked on board and up part number, about 6.00 part. everything else looks ok, just little smoke residue. J Tube in bottom compartment was dark in one spot, clogged. .. and either I just broke it when I moved the tube it was connected to, or it was broke before opening, but from the end of last early spring?? so a while since the system was in use! was curious if any other componenet or part on the furnace would cause the power relay to burn on the board? to bad the light codes do not reveal anything! So was considering removing power relay from the board and resoddering new one in... same specs on part. worst case buy a new board and install. (tracking the settings and details from old board). Appreciate your insight for a cost effective, but good fix.. before it get cold soon. Thx Eric, MN

[@grayfurnaceman]

Could be a short in wiring. Try disconnecting the outdoor unit to see if it stops. GFM

[@Veritech05]

The fuse on the board blows when I turn the thermostat to cool. Please help

[@grayfurnaceman]

The NO should go to the fan motor if I am understanding you correctly. GFM

[@erice.5844]

PS.. a question as well... The furnace is old, but hopefully getting a new board fixes it?? IE what caused the board to fail? trying to DIY, but even if a repair guy came to replace the board for an obvious... black square block burnt out? the same thing could happen unless you had a repair guy with insight and care you seem to have to look beyond the end of the day paycheck, and easy fixes.. but still cheaper than a whole furnace replacement. on a tight budget now so why my DIY.. Thx

[@grayfurnaceman]

Thirteen year old furnace is just broken in. Life is 20 to 25 years if set up correctly upon install. Burned spot is meaningless as it is a resistor that is designed to dissipate heat. What are the error codes? GFM

[@erice.5844]

@@grayfurnaceman Thx for reply.. ! System was powered but not in use..(heat only use)? Noticed blank screen on thermostat .what brught me to open up furnace to check things out. Current board when powered shows a solid green and red light, meaning no problem codes, everything ok? funny but true. Just have Heat and the central air fan that activated when trouble shooting the blank screen on the honeywell thermostat. Also looked up bpard for my (Tappan) Nordyne Furnace FG7SC 072D-24B, (92.1 efficient gas forced air)( Parts Circuit Board for G7/M7, sku 920915) 150-200.00 and the burnt out POWER RELAY.. looked on board and up part number, about 6.00 part. everything else looks ok, just little smoke residue. J Tube in bottom compartment was dark in one spot, clogged. .. and either I just broke it when I moved the tube it was connected to, or it was broke before opening, but from the end of last early spring?? so a while since the system was in use! was curious if any other componenet or part on the furnace would cause the power relay to burn on the board? to bad the light codes do not reveal anything! So was considering removing power relay from the board and resoddering new one in... same specs on part. worst case buy a new board and install. (tracking the settings and details from old board). Appreciate your insight for a cost effective, but good fix.. before it get cold soon. Thx Eric, MN

[@grayfurnaceman]

@@erice.5844 So, you are saying the burnt part is a relay? There are usually 2 relays on the board. One for the inducer and one for the fan motor. I can't see where the blank screen on the thermostat would be connected with the burned relay if the board lights are on. Are you sure the thermostat is ok? Is there power to the thermostat? Is it battery powered? GFM

[@BerettaM9USAF]

Basically IF you take it upon yourself to 'repair' the board in a court of law YOU have now assumed ALL the risk & loss, including any liability b/c it is now considered a 'modified' part. Save a client $ today and you may have a lawsuit tomorrow, people are way too litigation happy these days. Too bad b/c most of the techs in every field I know used to do 'favors' for folks. now they don't.

[@glasser2819]

no one likes when their house burns down.... those nice-guy favors can get turned back on you quickly, totaly agree!!

[@dwrldgster3151]

Mine gets volts when I tap on relay. The hot surface ignitor isnt getting power.

[@grayfurnaceman]

Sounds like a new board to me. GFM

[@Hvacmania]

will the board tell you if the board is faulty?

[@grayfurnaceman]

There is no solid answer here. Some boards have a pass fail light blink but it depends on the manufacturer. GFM

[@jimbola77]

thank you for sharing!!!

[@grayfurnaceman]

+jimbola77 Welcome GFM

[@anthonysaponaro6318]

I just wanted to add something, for my furnace, I had a #2 blink code indicating a vacuum switch issue , I bypassed the vac switch , still had no inducer motor , I wound up installing a variable dimmer switch onto the door safety connectors and slowly added and reduced voltage through the door switch and was able to get the inducer motor to get spinning and once it got spinning , she would ignite after about 10 seconds of spooling up, I am going to go with a bad relay on the circuit board or a bad capacitor on the board being I am decreasing and increasing the voltage and am able to get it to work time after time , my new circuit board should be in, in a few days because I am getting tired getting up every 2 hours to re-start it , to shut it down I have a hand held remote control on/off thermostat wired to the thermostat poles and now when I want to start it , I just click on off /on off on off about 15-20 times and it will start however now what I have noticed is happening is , the inducer will start for a minute then cut out /on /out on when this happens I know it is not going to run and I will have to go back to the variable dimmer switch connected to where the door switch used to be, shut off the power to the board completely for about 10 second , then click it on and it will start after about 10 on /off cycles without the inducer motor failing . . . .yes I know this is quite unorthodox way to run the furnace , but it will not run any other way , first of all the blink code is wrong and I don't know why it is saying Vac switch, it also is not the door switch because that and the vac switch were the first things I bypassed as well as the thermostat . . . .anyway, just wanted to throw that in there , Excellent videos by the way, very informative