Unit Turns on, but Turns off While Still Calling for Heat
Coleman: DGAA056BDTA
I made a post almost a year ago about this issue, but now I have much better detail about the symptoms (we live in the south, so by the time I got around to digging deep into the issue, we were in AC mode).
Unit does pre-purge(?), I hear a click, the igniter glows, another click, flames, blower starts less than a second later, immediately another click, flame goes out, unit remains on blowing air, 15 seconds another click, igniter glows, click, flames, click, flame goes out, 15 seconds, repeat.
It goes through the click, light, flame, click, no flame cycle five times. This entire time, the status light is solid and the unit is blowing fan-only air. After the 5th time the status light gives the one flash status code (Ignition Failure) and the unit turns off completely after about 30 seconds.
If I turn off the thermostat or lower the temperature to where it no longer calls for heat (it was still calling for heat), the status light goes solid again. If it turn it back on to heat or raise the temperature to call for heat, this process starts all over again OR if I do nothing and wait about an hour or so, it tries this process again. I don't think the site allows me to post a vid of what I see through the circular viewfinder.
Before I call in the repair guys...flame sensor? It's a much older unit where three wires goes into burner assembly (two white - HSI, one yellow - FS).
Side note: The AC portion of this unit works flawlessly.
After testing for thermostat issue..... clean the flame sense rod. It's a piece of stainless steel rod.
Take it out and polish it good with a green Scotchbrite pad. No need to replace it.
Is there any guidance on how to get to and clean the flame sensor based on this setup? According to the wiring diagram, the yellow wire is the flame sensor. It would appear that I'd have to disconnect the gas line and remove the entire assembly to get to it (the three wires go back to the circuit board via spade(?) connectors).
I removed and cleaned the flame sensor (had to Google how to replace the hot surface igniter to see how to get to the FS). It worked fine for about three days then the issue started again. To my embarrassment, when I went to clean it a second time - this time using fine sandpaper instead of a scotch pad, I damaged the assembly.
$160 later, I replaced the entire burner assembly which included the HSI and the flame sensor. Been almost two weeks with no further issues. Thanks!!
The furnace drain line goes through the furnace via elbow, then down to the pump. First original pvc elbow cracked within a couple of years. I replaced it with a perfectly good copper elbow from scrap, which I thought will last forever. However, this morning I woke up to wet floors and this elbow destroyed. Can someone explain the science behind it? Should I go back to pvc elbow?
[img]https://cimg3.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/20210110_101505_772663541a45b7404c063bbe62a7dc3bc575b5b8.jpg[/img]
[i]The ends are eaten away and it is cut in two places.[/i]
Hi Experts, my furnace experiencing short cycling (heat for ~4 minutes and then limit switch trips) this season and after some troubleshooting could not identify the cause, except for the blower motor RPM being below spec. Would really appreciate any advice or guidance.
Setup:
Nest Thermostat
Carrier furnace 58GFA085-JC circa 93
truesteam humidifier ( issue happens even when humidifier is disconnected)
[img]https://cimg4.ibsrv.net/gimg/www.doityourselft.com-vbulletin/801x1080/2021_01_12_15_55_13_5904e92729c3cf354432daa2d85e0bad97332c3a.png[/img]
[i]Furnace Label[/i]
Issue: even on a low merv mesh filter the limit switch gets tripped after a few minutes of heat. Pleated filters tript the unit much faster. Without filter unit works for a long time without any interruption. I verified the limit switch is the trigger by having a volt meter on it while running with 0 volts and then seeing 27v when heating stops.
Tests performed:
1) Static pressure. all registers are open, did not see any obstructions on return duct. I saw 0.38 as the highest SP from before the filter to the top of furnace
[img]https://cimg9.ibsrv.net/gimg/www.doityourselft.com-vbulletin/564x1080/2021_01_12_16_00_09_bb5d8d43d5c0bad1d47118c77c300c982e950d0b.png[/img]
I get 0.2 from before filter to after AC coil
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And -0.1 drop from filter to blower box, pressure on filter is 0.15
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[img]https://cimg2.ibsrv.net/gimg/www.doityourselft.com-vbulletin/619x1080/2021_01_12_16_06_38_613e215f952c1970053226261d24f62074777b2d.png[/img]
2) Looked for obstruction on coil and furnace. Found no issues
[img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1087x1080/2021_01_12_16_08_07_18e6ba55fd08b08a8e7af4303adf5f66d217d694.png[/img]
3) tested for cracks in heat exchanges using the match test and CO meter, nothing found
4) Tested 170f limit switch with controlled hot bed, switches open at 180f and closes again after a few seconds when removed from heat.
5) check draft. no obstruction on exhaust duct, draft motor spins at 3456 RPM, spec is 3300 so looking good
6) Check amps, showing 6.2 amp drawn on the whole furnace. Did not check the actual blower motor but figured that's the main consumer. I am on the HIGH speed setting for the blower.
This unit calls for max 10.1 amp on the motor so seeing 6.2 made me go and check the RPM. spec calls for 1075 but the most I was seeing is ~940. This is with the blower box open, I assume it will be lower when the box is closed?
[img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/877x1080/2021_01_12_16_20_58_8c5acfa66e014336bb6015bad8dc5041a95c1da4.png[/img]
[img]https://cimg8.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1920x1043/2021_01_12_16_48_17_a36a035a2bdc7afaa07a8a0c86245f97c2bb31a1.png[/img]
The fins are a little dusty but not more than 1 or 2mm dust thickness
Could it be that the motor got weak over time and not able to push enough air to cool the exchanger? Or maybe something else cause the exchanger to get hotter than prior seasons?
I'm not 100% certain but I don't think I've seen this issue in the past 10 years, even when I was using high merv pleated filters.
Thank you so much for looking and any advice.
12-08-20, 11:00 AM
