Gas Furnace Troubleshooting- Why the Sequence of Operation is Important!

[@acservicetechchannel]

Tool List- www.amazon.com/shop/acservicetech Support- www.patreon.com/acservicetech For those that are looking for the tools used in the videos: (Linked Below) Here is the link to the Fieldpiece SDMN6 Dual Pressure Testing Manometer with Pump-amzn.to/2jyK5Ka Here is a link to the UEI DL389 Multimeter used in the videos- amzn.to/2av8s3q Here is a link for the Supco Magnet Jumpers amzn.to/2gS4h6z Here is the link for the Irwin Wire Stripper/Cutter/Crimper amzn.to/2dGTj2V Other tool links can be found in the video description section. ACSERVICETECH is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

[@skaterwig]

I’m an hvac tech with 4 years in and your videos are so helpful. Mechanics don’t really wanna teach this stuff, love it!

[@acservicetechchannel]

Glad you like them!

[@harh3101]

Fasinating, I was a licenced contractor for many years but never paid any attention to the HVACR I had a good repair man. Now I am retired with plenty of time finding out what I missed.

[@tapanco67]

i work as maintenance and yours videos really help me alot thanks

[@acservicetechchannel]

Thanks a lot Jose!

[@billmossII]

Thank you for doing this. Great job.

[@ElementofWorship]

This is a great video, thank you for posting!

[@acservicetechchannel]

Thanks Element of Worship!

[@papajoe3832]

Super clear video. 7 steps (phone # digits) was great & accurate. Appreciate 24 V problem references and being able to clearly hear your Vx over equipment operation. As suggested above, using a gas combustion analyzer be helpful in conjunction w/ startup sequence. Seeing some HVAC tech YTubers heavily looking at combustion elements. Thanks for your time & energy sharing your always safety-first experiences. Keep up the great work please.

[@acservicetechchannel]

Ok thanks Papa Joe!

[@geoa9722]

You're awesome , man! Thanks a lot for the great explanation!

[@acservicetechchannel]

Glad to help George!

[@herculesskinny2030]

I will give you 10 out of 10 on my score card, detailed explanation in my opinion.

[@acservicetechchannel]

Thanks a lot Hercules!

[@zummliller]

ac, I always find combustion analysis helpful. Please consider doing one

[@acservicetechchannel]

Ok thanks Joe!

[@blueg3027]

If you do a combustion analysis for every furnace service then I would call you a liar lol

[@robbicano]

Excellent lesson sir!

[@acservicetechchannel]

Thank you Beno Davis!

[@waterheaterservices]

Most helpful lesson. Thank you sir.

[@acservicetechchannel]

Glad you enjoyed it Jim!

[@spartan5106]

good stuff!

[@Azaion91]

4:04 is gold

[@papoloco34]

great video like always.... excited for the next one👍👍

[@acservicetechchannel]

Thanks Pedro!

[@papoloco34]

and I still waiting for the one's that I tell you😃😃

[@acservicetechchannel]

I do remember the wiring diagram and pms you were looking for. I do plan to do them in the future. Right now its just trying to get some videos out with the crazy schedule. Thank you

[@papoloco34]

no problem man...keep it up!!!

[@tboneproductions2453]

Fantastic job of explaining the op sequence. Thank you for taking the time

[@acservicetechchannel]

Thanks Tbone!

[@SombraLocs]

Excellent video!

[@acservicetechchannel]

Thank you, nice to hear from you!

[@Kinslayerx1]

Came here to brush up on the SoO for gas furnaces, got a final coming up covering Gas Furnace Trouble shooting and the likes...ended up finding the playlist and watched them all...lol

[@acservicetechchannel]

Very nice Ryan and good luck on the test, thanks! Is this a college or field test?

[@Kinslayerx1]

AC Service Tech LLC college, however it’s a lab style hands on test. So my instructor will likely be replacing parts in our labs gas furnaces with non-functional parts to simulate real world problems, busted pressure switches, busted igniters, dirty blower motors that kind of stuff, he’s very adamant about making sure we face real problems instead of “disconnect a wire here or there” so I’ve been watching your videos to supplement my class and lab time. Hell he’s started showing us a few of them in class as well

[@acservicetechchannel]

Very nice, that is what I do in class and found very creative ways to break the units in a way where it was still safe enough for the students to troubleshoot, very nice! Tell him that I think thats awesome and appreciate his diligence toward you all!

[@lancerudy9934]

The hsi how many amps does it draw?

[@jimbola77]

excellent video!!!!!

[@acservicetechchannel]

Thank you Jimbola77!

[@deletedaccount5250]

Good and clear thanks

[@acservicetechchannel]

Thanks for comment Ahmed!

[@tapanco67]

real good info thanks

[@acservicetechchannel]

Thanks Jose!

[@indiantraveller194]

Very niece sir 🇮🇳😘

[@yonderosa]

outstanding! Thanks!

[@acservicetechchannel]

Thanks JR!

[@basilboolis7708]

Thank you so much for this great video !! Can you please share sequence of operation on Rooftop unit for AC

[@acservicetechchannel]

Thanks for letting me know what you would like to see!

[@drummerdem50]

Excellent!

[@acservicetechchannel]

Thanks Drummer!

[@donio71]

Hello buddy,can you do a video on high efficiency boilers for us?by the way u r the best

[@meerscan9101]

great video...

[@acservicetechchannel]

Thank you Refrigeration Tech!

[@Cartjayden]

Furnace issue- Sequence of operation satisfactory, up until the blower to come on. But works with AC? Any thoughts

[@teblake3]

Thank You!

[@acservicetechchannel]

Thanks Tom!

[@sergiodoordie319]

good video gracias mister

[@acservicetechchannel]

Thank you Sergio!

[@fredd8140]

excellent

[@acservicetechchannel]

Thanks Fred D!

[@steveo7624]

like the magnet trick i use a small clamp

[@acservicetechchannel]

Thanks Stephen!

[@gonzgarr1592]

nice info

[@acservicetechchannel]

Thanks gonz!

[@HieuPham-gg9uj]

I have a question.What if the blower is not running, the high limit switch will shut off the system or the IFC will turn off the system? Thanks for all the great videos.

[@acservicetechchannel]

The high temp limit switch would normally open up the limit switch circuit and the ifc would shut down the flame, thanks

[@HieuPham-gg9uj]

Thank you so much. I really appreciate it.

[@chupalia]

good stuff

[@acservicetechchannel]

Thanks chupalia!

[@Pretzel114]

Hello ACSERVICETECH!!! sorry I have not been on for a while, my building complex I work at had a fire and I been pretty busy installing new units, which are all new gas units from the old oil ones we had. One question, when the hot surface igniter lights, does that also send a signal to the board to allow the 24v to flow to the gas valve? You may have covered it and I missed it. Great video thanks again.

[@acservicetechchannel]

Hey nice to hear from you, wow thats crazy. To answer your question the hsi is powered for a specified amount of time and the unit does not know whether the hsi is red, broken or even there. It will then only open the gas valve by applying 24v for about three seconds while the ground connected to the board that is there for the flame rod is continually searching for a dc micro amp signal to verify the flame. It will likely send three seconds of gas three times before it will lockout for several hours unless the power is turned off and turned back on.

[@Pretzel114]

acservicetech Thanks acservicetech! that makes sense, I was not even thinking of it like that. Great stuff on your video's. if I don't talk to you by then have a good Thanksgiving.

[@acservicetechchannel]

Have a Great Thanksgiving NICK-O!

[@zummliller]

do a combustion analysis. thank

[@enzoamore9173]

Is the pressure switch set for normally open or closed?

[@acservicetechchannel]

In newer furnaces they are typically normally open but in some older furnaces especially ones without control boards, both the normally open and normally closed contacts are used to control what happens, thanks!

[@jameswestii454]

Question: I have a Lennox gas furnace M #78RGF3-75-1 and a Rheem AC unit controlled by my Nest T-Stat. Furnace installed in 1994, AC in 1995 and Nest stat a couple years ago but all have work great. 2 days ago stat says no power to RH wire detected, E24. AC unit works as normal but no heat at all. Any thoughts what could bring this on all of the sudden? I had a technician come take a quick look and he says furnace control board is shot and I need a whole new furnace but if that was the case wouldn't the AC not be working as well? They want to just replace furnace witha Bryant and leave the Rheem (R22) AC alone but I thought that old and new units typically don't mix well, especially this old. Help!!!

[@acservicetechchannel]

You could check to see if you have voltage from rh to c which should be 24-19v and then check from rc to c and you should get the same voltage. That doesn't sound right as you only have one power wire going and connecting to both rh and rc. It is not like it is two separate systems. That stat is all controlled by the one furnace and if the ac works then it sounds more like something is fishy with the stat. If you jump from the 24vrc/rh wire to w, does your heat turn on? If so then the problem is in the thermostat, thanks

[@jameswestii454]

AC Service Tech LLC Thank you very much. Will be checking what you asked tomorrow. Appreciate your time!

[@kingbagger3599]

Question.. working on furnace now and after hsi glows the gas valve never receives power to open. That comes from board correct?

[@acservicetechchannel]

Yes the gas valve is powered from the board if equipped. Make sure to read the gas pressure with a manometer if you do have 24v to the gas valve

[@timvowels506]

I am dealing with a similar problem. Hsi kicks on. Hear the valve click as the bord sends 24v to gas valve. Gas valve opens for 2 seconds then signal cuts out. Ironically can introduce 24v from separate source to gas valve in sequence not comming from circut bord. The system cycles fine as I manually introduce power to valve. Gas pressure seems to be fine. Just wondering why the gas valve power is cutting out on start up.

[@zgaming6341]

Great video, I heard you say you were going to make a video diagnosing each stop on the sequence of operation. I was hoping you had a link. Thank you

[@acservicetechchannel]

Hey Zach, so here is the Gas furnace troubleshooting playlist. ---- kzbin.info/aero/PLxnHR5_D2ojyN6VClLntbM4X82Gc9Xs8A ---- In it you will find each of the sequence of operation components and the reading wiring diagram schematics will also get into the heat and flame rollout sensors before the sequence of operation. It is too much for one video or at least it would not be as much of an in depth video. Just pick out the videos in the sequence and whichever blower motor you would like to learn about. Thanks

[@zgaming6341]

Awesome this is what i have been looking for. Thank you. I enjoy all of your videos.

[@acservicetechchannel]

Great to hear Zach!

[@laurielammi3996]

I want to know if its 24 volt ac or dc on circuit board or combination of ac and dc?

[@acservicetechchannel]

the 24v is ac only. The only dc is the micro amps due to flame rectification, thanks

[@fredmcallister6217]

Hey can u do a video checking a furnace with a fieldpiece sdmn6? i bought this meter and dont really know how to use it.

[@acservicetechchannel]

That would be something that I would do in the future, yes. Thank you for letting me know what you would like to see. Since you asked me if I was from Cape May, are you related to the McAllister Service Company in Atlantic County?

[@fredmcallister6217]

acservicetech no but i seen them around. im from the mt laurel area (Burlington County) and i just recently moved to Charlotte. but i still come to New Jersey alot! i wish i coud sit in on some of your classes lol.

[@acservicetechchannel]

Thanks for letting me know what you would like to see. I would like to put something like that together but I can't give you a time frame yet on it. Thanks Fred.

[@fredmcallister6217]

acservicetech thanks!!

[@eadamson64]

the 2 wires coming off of the inducer motor (brown and brown/white stripes) whats the function of the switch they are wired into? I know the pressure switch is what tells the unit the inducer is on but not sure what this which does

[@acservicetechchannel]

Hey Eric, check this video out on the inducer motor and those cap wires to answer your question-----kzbin.info/www/bejne/b6SxhnSpfquKack ------ Here is one on the pressure switch----kzbin.info/www/bejne/aIO1mZyBoq9sf9k

[@eadamson64]

acservicetech thank you for the links to the other videos. I really enjoy watching your videos... keep up the great work!

[@acservicetechchannel]

Thanks Eric. It seems that those small black capacitors like you are mentioning for the inducer motor really don't go bad that often compared to standard ones you see. Still check them and make sure that they are in range.

[@slappahoe8493]

Does anyone know his follow up videos for this? Pls lemme know

[@acservicetechchannel]

Look up "acservicetech furnace troubleshooting playlist" for many videos on this, thanks!

[@guitarhvac]

Great video. I've been in the field for a couple years now. I have a question. The guys at the parts house where I bought my last split unit could not answer this question.... Kinda scary to me that they can sell equipment and say it's matched, but not be able to explain the sizing, but anyways..... My question is about sizing a gas furnace to a coil on a split system. I bought a 3 ton split system and it came with a 60,000 btu 80% gas furnace. I know that's the input, so the output would be around 64,000 btu's.... I've always been taught that 3 tons of a/c would be removing 36,000 btu's of heat..... 12,000 btu's per ton. If a customer were to look at the rating label on the furnace, I would not be able to explain it. Any help in clearing this up would be greatly appreciated.

[@acservicetechchannel]

Sure, no problem. First lets look at a 60,000 btu furnace at 90 % efficient. Lets use a Payne number such as PG9MAV042060000. The 60000 is btu/hr input and 54,000 output. This comes with a blower that is capable of moving 42,000 btu/hr of cooling on the high speed, so 3.5 tons. Figure the cooling load first then match the blower speed or have the blower speed be higher. In this case set the 42,000 btu/hr blower capacity to 36,000 with the dip switches to match a 36,000 evap and 36,000 condensor. Thanks

[@guitarhvac]

I'm sorry, I just looked back on my first message I sent. I had my math figured wrong. Idk why I figured the math on 80,000.... The furnace I bought was was 60,000 btu input so the output would be 48,000 btu since it's an 80% furnace..... so are you basically saying just size the blower to the cooling coil tonnage?.... I did notice the furnace is rated at 1200 cfm, which is 400 cfm per ton so that's right.... I'm still kinda unclear on the heating btus..... 48,000 btus sounds like it would correspond to a 4 ton system if figuring 12,000 btus per ton....?

[@davidhilson7607]

De@@acservicetechchannel

[@chrismiller6579]

Hi, I have an odd problem, and I think I know how to fix it, but I seek confirmation from someone with greater experience than mine. The inducer runs. The flame ignites for no longer than a second and goes out, so the igniter is working perfectly. The cycle repeats. On a cold morning, this will repeat for hours. I have cleaned the flame detectors. There are three probes distributed across two flames. The flame detectors might be marginal, or the gas valve might be marginal, but once the heater "gets going", it works. This morning, I switched the electronically controlled gas valve off for ten seconds. The inducer ran for the entire ten seconds. When I switch the gas valve on, the flame ignited and stayed lit. I haven't done that before, so I don't know if I have observed a coincidence or an actual "cause and effect". I think I can diagnose the failure of the flame to survive more than a second. Either the gas valve is malfunctioning by arbitrarily shutting off, or the flame detectors are malfunctioning by failing to detect a flame. Since flame detectors are the least expensive to test and/or replace, I want to test them first. Since this furnace will run, I fear I am dealing with something marginal that I might not recognize when I see it. Can you advise me?

[@acservicetechchannel]

flame sensors are typically just a stainless steel rod that has ceramic around it and it puts 80-180v into the flame. They don't ever need to get replaced except in the case on small ones like on smart valve units. You may want to check your grounding and you do need to clean the flame sensors though with unsoaped steel wool. Are you checking flame rectification with the multimeter?

[@DECIFERTHIS09]

Furnace sequence of operations 1 blower 2 inducer motor 3 pressure switch 4 orange in glass sight 5 gas valve 6 flame rod 7 blower motor delay

[@acservicetechchannel]

Thanks David, some furnaces don't have a light on their board and some don't have a board but just relays, thanks a lot David!

[@panik16k]

David Pierson right idea but not quite correct.

[@jimbarron8688]

Assume: customer switch contacts closed. 1. Thermostat calls for heat R-W. Initiates self-check of pressure switch circuit to ensure pressure switch contacts are in OPEN position. (this is in addition to the heat safety circuit being constantly monitored for all switches in contacts CLOSED position). 2. Ventor motor receives 120 volts. 3. Pressure switch contacts closed if all parameters of venting system are OK. 3. HSI receives 120 volts and if ok begins to power up to temperature (orange glow). 4. Gas valve is energized. 5. Combustion occurs if all parameters of gas for combustion are OK. 6. Flame rectification at flame rod occurs and IFC senses combustion has been successful. 7. Main blower is powered after delay. 8. Thermostat satisfied and contacts open. 9. Gas valve is deenergised. 10. Combustion stops. 11. Vendor motor powered off after delay. 12. Pressure switch contacts open. 13. Furnace awaits next call for heat.

[@DrunkBeast88]

Correction… carrier brand furnaces are the only ones that run the blower on power up with a heat call…

[@MrOhiousa]

My inducer comes on way before the blower shuts off. then the blower shuts off and the inducer keeps running but my furnace never lights up. flue pipes clear, pressure switch ok, inducer ok. is my IFC board starting the sequence of operation too early?. should I replace the IFC board?. Thank you

[@acservicetechchannel]

Depending on the furnace, the inducer coming on while the blower motor is running right after power up can be normal. The inducer motor will run, then you would test between the pressure switch power wire coming off of the board and 24v Common C terminal for 24-28.5v, then check between the pressure switch 2nd wire coming off of the board and common C terminal for 24-28.5v. If your HSI then does not get 120v and your high heat sensor and flame rollout sensor wires are allowing 24v back to the board then yes your board would be bad if it is a board and hot surface ignition system like this. If it has a spark ignition you need to make sure that it does not have another board for that. If your hsi has 120v and isn't turning red then the hsi is bad. Thanks

[@adame5238]

I hope you checked the secondary! 🤣

[@blueg3027]

Looks like a carrier.

[@acservicetechchannel]

Yeah that is a carrier/bryant/payne

[@enzoamore9173]

You forgot the roll out switches in sequence of operation.

[@acservicetechchannel]

Hey Enzo, those are part of the safeties and when I say the sequence of operation, I just mean moving parts or actions that take place, otherwise the sequence would include the interlock switch and other things as well thanks!