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I have a 2-stage Bryant 880T furnace that was installed by a local company for the previous homeowner in 2021. This morning I woke up too drat early (yay brain that won't stfu) and I noticed that my furnace was short cycling trying to recover from the overnight 60degree setpoint. A bit of "Its 4:30 AM and I got poo poo to do" observation later: 0:00 - start, inducer on high 0:33 - gas on 0:34 - ignition 0:45 - inducer to low ~1:25 - blower start, low speed 17:00 - blower to high, inducer to h 24:40 - gas off, inducer off, blower to low, thermostat still calling heat - board blinks code 3-2 "Low-heat pressure switch did not close or reopened" 28:50 - blink stop, inducer on 29:25 - gas on, ignition 30:00 - fan to high 34:50- gas off, inducer off, blower to low, thermostat still calling heat - board blinks code 3-2 again 39:20 inducer on, I shut the system down shortly afterward I figured out that the furnace wasn't wired for the two-stage thermostat to control the staging because of course it wasn't that would require fishing a new cable to the thermostat location and Gary had a supernatural ability to pick cut rate contractors and let them get away with poo poo work. So it is set to automatically switch between first stage heating and second stage heating when first stage heating takes too long (default is 16 minutes, but it will reduce the first-stage time the longer the second stage ran for in the previous cycle). I found the Installation manual for my furnace and [url= https://d1049ui2fjityy.cloudfront.net/userfiles/inriver/documents/t5/-8/5_/troubleshooting%20-%2058-5t.pdf%A0]troubleshooting manual for the carrier equivalent furnace[/url] which is identical as far as I can tell. Going by the operation sequences listed my furnace is running pretty flawlessly at startup. Appendix F also includes the automatic staging algorithm if you are interested There was a dip switch to disable this automatic changeover, allowing the furnace to run in first-stage unless second-stage is called via the W2 terminal (which is run to the outside of the furnace but not run to the thermostat because they reused the old 5-wire). When the system is limited to first-stage operation it runs indefinitely, no shutdowns. Forcing it to run in second stage by jumpering W1 and W2 causes it to shut down at 11:20 and continue to short cycle. Going through the troubleshooting sequence for code 3-2 on pages 27-29 and ended up at step 44, which is the start of checking to verify that there is enough pressure present to close the low-heat pressure switch when the system throws the low-heat pressure switch open error. I didn't do it because I don't have a manometer, but it also seems a bit superfluous since the system running at second-stage heat indicates that the higher pressure high-heat switch (0.27" break) is staying closed so there's definitely enough pressure to hold the low-pressure low-heat switch (0.18"break) closed. If the high-heat switch wasn't staying closed then the system would throw code 31. Annnnyway, new low-heat pressure switch I'm guessing? The mounted part is BA20265 or HK06MC110 for the assembly but I can't find that anywhere but used parts on ebay. Now you might be wondering why I did this troubleshooting myself and would replace a faulty switch for a system installed in 2021. Well the local company got absorbed by a regional do-everything home services company and when I called to have them look they said there was a $120 minimum diagnostic fee plus labor for any warranty work and they immediately tried to sell me on a long term service plan. I guess I also want to confirm there's no harm in running the system at first-stage heat other than it taking longer to warm things up.
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Dec 8, 2023 03:06
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| # ¿ May 4, 2024 05:36 |
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I guess I can toodle over and take a peek down it sometime tomorrow, it is on a roof section that is pretty easily accessible for a second story window. Again though wouldn't that throw a high-heat switch error since any obstruction or loss of draft would keep it from pulling the required higher vacuum and open the higher pressure switch first? There is no intake, the furnace is in a utility room and pulls in interior air.
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Dec 8, 2023 03:22
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There's practically no lateral span to the vent, maybe 3 feet over in 15 feet up, and little lateral there is was done at 30° and 45°. Only thing I can spot that is iffy is they used single wall from the furnace until they reached the ceiling penetration where they switched to b-vent and a rated collar. I might hook the multimeter onto the switch just to see if it is actually opening or not. Ah dammit I just realized I didn't trace the switch wires and make sure they were seated well at the connectors and on the control board. I loving swear if this is just a loose connection... I'll be happy to save some cash.
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Dec 8, 2023 04:16
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Good call. I went ahead and ordered the switches as well as the manometer + tees + tubing. I set a reminder to order a capacitor in a few months. As a positive part of this kerfuffle I figured out that I can wire the thermostat to control heating stage without running a new cable. I can use the ecobee power extension kit (which the previous owner left in the box) to eliminate the need for the black common wire, then repurpose that common wire as W2. Just gotta be sure to clearly label everything for future me.
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Dec 8, 2023 18:05
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So the good news is that the vent looks clear and the draft pressure holds steady right where it is supposed to be at the time of shutdown and error, so there's not anything fucky there. The bad news is the voltage across the pressure sensor also holds steady at 0.00V AC until the inducer motor shuts off and the pressure drops past the break point of the sensor, and it seems like the flame doesn't cut out until the pressure sensor opens. There's a distinct relay click when the inducer turns off, and the motor is quite hot several minutes after shutting down. Since I'm waiting on my pressure switch anyway I'm running it monitoring the voltage going to the inducer motor to see if it might be tripping a thermal shutdown in the motor. Edit: yep. Voltage is still supplied to the inducer motor when it shuts down but the motor stopped spinning. The infrared thermometer reads over 215° on the yoke. Welp. Shifty Pony fucked around with this message at 16:25 on Dec 11, 2023 |
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Dec 11, 2023 16:20
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I might actually just throw in the towel and call up the installing company to come out for a warranty replacement. It is a two speed unit and the cost of the motor assembly is significantly more than the callout fee.
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Dec 11, 2023 17:32
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Well, the technician came out yesterday afternoon and confirmed that the inducer motor was overheating on high. Everything else with the system is operating perfectly. He was unable to see any inventory for the part because apparently carrier has discontinued the inducer part and substituted in another. They won't say what the substitute part number is; you have to call. He called but got placed on hold for a while and then automatically sent to voicemail the instant the clock ticked to 4:30 PM (when the local Carrier parts warehouse closes). This morning he was able to get through and they said that they had the bare motor in stock but the housing assembly that went with it was backordered. He went by to see the motor in person to compare to photos he took of the current one to figure it would be possible to install just the motor, but when he got there to pick it up it was not the right motor at all. So now we have to wait for the entire inducer assembly to be backordered and shipped to the local warehouse. The estimated turnaround is over a month.
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Dec 12, 2023 17:52
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I think we're just in the appliance equivalent of the automotive Malaise Era. Companies are trying to rig discrete electronics and on/off sensors to implement increasingly complex control schemes using components that are essentially old technology with some minor tweaks to allow integration (but which also wreck cross compatibility). Except the appliance companies don't have the same excuse that the car companies had because integrated systems capable of reliably implementing control schemes much more complex than any home appliance would ever need are extremely well proven technology. Appliance manufacturers are trying to make an unholy complex abomination of a carburetor work when there's a direct fuel injection system right loving there they just need to bite the bullet and learn to use it.
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Dec 12, 2023 19:28
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20 minutes sustained second-stage operation without a hitch when it would shut down after 12 before. New inducer motor gets warm but it seems to be coming from being adjacent to 400°F exhaust. It settles into a steady state while running.  I'm going to hold onto the old motor until the installing company calls saying they got the warranty replacement, then swap it back in so they can install their replacement. I'll keep the assembly I got as a backup and eat the $600 labor charge as the cost of keeping the (two year old!) system under warranty for a bit longer in case something stupid expensive breaks. Edit: the thermostat is also now wired to properly control furnace staging. Shifty Pony fucked around with this message at 12:00 on Dec 22, 2023 |
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Dec 22, 2023 11:24
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Actually I'm reconsidering now, might just cancel the replacement and say gently caress it to the warranty since the company that bought the installing company is known as being very expensive and any expensive part beyond my ability to swap in is going to come with such a stupidly high labor charge to replace that I'd almost certainly be better off going with a different HVAC company.
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Dec 22, 2023 18:58
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Hungry Squirrel posted:I had some furnace trouble over the last few days (Trane error code of four red lights) and the service tech says that the condensation in my furnace flue (on the roof, single-story house, insulated attic) freezes and chokes the airflow. His suggestion is to get on the roof to clear the blockage and adjust the flue cap (which is not going to happen in this weather), but that a short-term fix is to crank my thermostat to at least 80 for a few hours every night before I go to bed, then shut the system off overnight. The ice is forming at the start of every heating cycle when the walls of the flue are freezing cold. Normal running will cut off before the furnace exhaust reaches equilibrium and has enough time to melt that ice, then restart later forming another layer, etc. Running the furnace for an extended time should get the entire flue hot enough for long enough to melt any condensed ice.
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Jan 19, 2024 17:56
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Hungry Squirrel posted:It is high efficiency, and the tech said that this can be related, because... reasons? It had to do with the amount of output being different, causing a mismatch elsewhere in the system. The exhaust of a high efficiency furnace is ~100°F vs ~400°F for a traditional 80% efficiency furnace. The cool still-moisture-rich exhaust of a new HE system is much much more prone to freezing than the old 400°F blast, which leaves a lot less wiggle room to get away with an improperly sized or routed exhaust system. It's also possible that the exhaust vent is so badly matched to the HE furnace that the furnace won't ever be able to actually melt the ice at the coldest early AM temperatures, so the tech was telling you basically to bank as much heat in the house as possible and shut the system down to keep it from running during those times. If you are able to you might want to message the tech and ask whether their temporary solution was intended to melt any ice buildup by running a long while or to prevent the system from running when ice buildup was most likely to happen (or both!).
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Jan 19, 2024 18:34
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That control board is basically handling all the standard switching and signaling to the furnace, the cable to the thermostat is a special proprietary communication link. The good news is you have white and yellow as well running to where the thermostat is, so you won't need to run new cable. You will need to bypass and remove that control board, possibly running new wires from your furnace/AC controller board to the green/red/blue/white/yellow cable (and on to the new thermostat). This isn't hard but if you are uncomfortable reading technical diagrams a professional might be a good idea.
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Mar 5, 2024 04:25
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devicenull posted:It's hard for me to tell if he's got enough wires there for it to work (or what they're even connected to)... I count at least 8 coming into the board from the furnace. Looks like this is the interface board: https://s3.amazonaws.com/s3.supplyhouse.com/product_files/THM5421C1008-Install.pdf and seems like Poque has a powered ventilator of some sort. That shouldn't be hard for a professional to loop into a traditional thermostat system.
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Mar 7, 2024 15:57
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He kind of touches on all of those, but he also blames many of the HVAC companies having dedicated sales staff, and the sales person isn't really incentivized to actually properly size the unit. The sales person doesn't want to scurry around the house estimating the actual thermal load they just want to get something in there as quick as possible, which means running a very basic calculation and then grabbing whatever the next size up that is in stock at their supplier. I do have several complaints about TC in general, the biggest one is that he seems to completely discount the non-monetary cost of things because he enjoys fiddling. There is value in not having to worry about keeping space heaters around as backup for when your main source of heat is unable to maintain temperature in a cold snap. He also glosses right over recovery time, and why that might be important consideration for people. It's like saying people only need a car with 30 hp because that's what it takes to maintain highway speeds. When the inducer motor on my furnace was unable to use the second stage and it was taking two or three hours to recover from our normal 62° overnight set-point temperature, that kind of sucked.
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Mar 7, 2024 23:06
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The fan and everything past the fan has to be in non-living space because a crack or bad seal before the fan will simply suck in air, but past the fan a crack will spew radon-rich air.
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Mar 10, 2024 16:34
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I mean the code is what I said, but to put on my Gary hat... radon ain't carbon monoxide. If you are borderline on radon without mitigation and keep a monitor going, I wouldn't feel at all bad about putting the fan in an easier to access spot. I would just be sure to have a professional reinstall it before selling the house.
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Mar 10, 2024 16:57
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His Divine Shadow posted:I'd like a multimeter that could do a simultaneous amperage and voltage reading, showing both values in the display. That requires two sets of probes, since amps are measured using a series arrangement (or inductive clamp) and voltage is measured in parallel. At that point two meters is more useful.
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Apr 5, 2024 16:08
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| # ¿ May 4, 2024 05:36 |
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Household voltages really won't cause a cheap meter to explode. Even if you do something really bad like measure across the incoming 240V while the meter is hooked up in un-fused 10A mode, the flimsy plastic case of a HF DMM is enough to contain the melted copper bits that will result. In my opinion the real dangers of a cheap lovely meter is that too much of your attention will be taken up with fighting your tool which could lead to you accidentally bumping your hand up against a live conductor, and the leads can easily fray internally to the point that they can't be relied upon to properly indicate that something is live.
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Apr 5, 2024 18:20
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