Furnace out - Locally sourced transformer?
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Brad Tissi
Dec 31, 2016, 11:58:20 AM12/31/16
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Does anyone know where to get a 240v > 24v 40A transformer locally?
EschewObfuscation
Dec 31, 2016, 12:39:25 PM12/31/16
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Um, uh... 40 Amps... that's not a typo? Just to be sure, we're talking about a several hundred dollar transformer the size of a small cantaloupe? I'm familiar w smaller 24 VAC xformers used to drive blower relays, gas valves etc, but am hard pressed to imagine what would use almost a kW at such low voltage?
Assuming that's not an error, I have no specific idea. But when I was shopping for a 3/4 hp blower fan, I did a bunch of research and repeatedly ran across praise for an outfit called Schepker Parts Supply in St Charles. They happened to be all out of what I needed, so I bought from a less satisfactory outfit. But Shepker has Saturday hours, so maybe you could call em and ask?
good luck
Assuming that's not an error, I have no specific idea. But when I was shopping for a 3/4 hp blower fan, I did a bunch of research and repeatedly ran across praise for an outfit called Schepker Parts Supply in St Charles. They happened to be all out of what I needed, so I bought from a less satisfactory outfit. But Shepker has Saturday hours, so maybe you could call em and ask?
good luck
Jim S
Dec 31, 2016, 12:45:17 PM12/31/16
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On Saturday, December 31, 2016 at 10:58:20 AM UTC-6, Brad Tissi wrote:
> Does anyone know where to get a 240v > 24v 40A transformer locally?
You could use one hot line to ground for 120 volt input. Not code but would get you by. also could use 2 12 volt transformer outputs in series. going to be hard to find anything on the weekend locally. Maybe two landscape light Transformers from The Big Box store to get you by for the weekend
Ben West
Dec 31, 2016, 12:48:48 PM12/31/16
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If you can locate exact brand / model # of identical or equivalent replacement, try Capitol Group on Fyler off Kingshighway (314-351-4900), or maybe Crescent HVAC near Hampton & I-44. The latter may balk and demand you provide a contractor license #, tho, and both locations definitely closed today.
Echoing the comment to verify the amperage. 4A or even 0.4A seems more likely, depending on what that transformer is supplying.
On Dec 31, 2016 11:58 AM, "Brad Tissi" <bti...@gmail.com> wrote:
Does anyone know where to get a 240v > 24v 40A transformer locally?
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Brad Tissi
Dec 31, 2016, 1:15:52 PM12/31/16
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Typed too fast. 40VA, not 40A.
EschewObfuscation
Dec 31, 2016, 1:18:54 PM12/31/16
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A pair of 12V lighting xformers sufficient to meet/exceed that current rating would run... 2 X $500, but immediately available at the home centers. I'd repeat the "are you sure of the rating" question. Mail order as spec'ed runs $400 or so, and that's chinasport manufacture. meh.
I have a pair of 120V 12/24V transformers on hand I'd be willing to lend, but even paired, they're rated only about 25 or 30A. They're each the size of a large grapefruit.
I have a pair of 120V 12/24V transformers on hand I'd be willing to lend, but even paired, they're rated only about 25 or 30A. They're each the size of a large grapefruit.
EschewObfuscation
Dec 31, 2016, 1:20:30 PM12/31/16
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woohoo, that's much better. If you need to borrow a much bigger than needed 120V you could patch in for temporary, I can do that. But call Shepker.
Brad Tissi
Dec 31, 2016, 4:00:24 PM12/31/16
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After calling around the suggested places, my coworker reminded me of our recent discovery when we were cleaning out the lab.
Once I test them out, I'll update on the progress.
Thank you for the help everyone.
Brad Tissi
Dec 31, 2016, 6:16:46 PM12/31/16
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Well, the 100VA unit sort of works, but not quite enough.
Depending on how the X1-4 contacts are jumpered, I can either get about 26VAC or 31VAC. Neither of which is apparently close enough for my Nest to kick on the heat.
Any suggestions?
Jim S
Dec 31, 2016, 7:47:23 PM12/31/16
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I work on hvac systems and 26 v should be well within tolerance. Must be other things wrong.
Brad Tissi
Dec 31, 2016, 9:52:37 PM12/31/16
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Good to know that I'm not crazy...yet.
I should mention the 26v is rms. 23.3v average.
There's got to be something going on with the control pcb.
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EschewObfuscation
Jan 1, 2017, 2:38:49 AM1/1/17
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Furnaces aren't very complex. My cranky old piece of junk has forced me to learn something about them.
If you provide 24V to the TH terminal (thermostat, call-for-heat) and it fires, it's the thermostat's fault, if not, it's the furnace's. (You disconnect the t-stat before that test ofc.)
If it's hot surface igniter, that's just driven by 120VAC, easily tested w your meter. Those burn out regularly like incandescent light bulbs, and for similar reasons; you should always have a spare on hand. If spark igniter, I'm not sure what that signal looks like and would not expose a meter to it in case it's a high voltage spike.
If you suspect the flame sensor, you can fake its signal, or apply a propane torch to help it along, see if that makes a difference.
If 24V applied directly actuates the gas valve (you should hear a click), it's absolved.
If 24V applied to the relay coil spins up the blower, that's absolved.
Don't forget to check for any interlocks on the TH line; some (maybe all) have snap thermostats in line with the TH line, intended to detect overtemp in the manifold. Those can degrade/corrode and go open circuit just over time. Some may be manual reset, which would disable you permanently if you don't know to push the reset button.
If you have a newer, fancier model with updraft fan, your controller may be sensing failure there and refusing to cycle further; manually test that like any other component.
Does yours have a CO or other gas sensor? I don't know if any do have those, but it's not beyond imagining; fake the signal there if so to absolve that.
If all those sub components work but it doesn't cycle, it's your controller, which is a replaceable (if ridiculously overpriced) module. (Mine contain maybe $5 of components, list price for $250. I'm in the wrong business.)
And if it passes all those tests and still won't run, call an exorcist.
If you provide 24V to the TH terminal (thermostat, call-for-heat) and it fires, it's the thermostat's fault, if not, it's the furnace's. (You disconnect the t-stat before that test ofc.)
If it's hot surface igniter, that's just driven by 120VAC, easily tested w your meter. Those burn out regularly like incandescent light bulbs, and for similar reasons; you should always have a spare on hand. If spark igniter, I'm not sure what that signal looks like and would not expose a meter to it in case it's a high voltage spike.
If you suspect the flame sensor, you can fake its signal, or apply a propane torch to help it along, see if that makes a difference.
If 24V applied directly actuates the gas valve (you should hear a click), it's absolved.
If 24V applied to the relay coil spins up the blower, that's absolved.
Don't forget to check for any interlocks on the TH line; some (maybe all) have snap thermostats in line with the TH line, intended to detect overtemp in the manifold. Those can degrade/corrode and go open circuit just over time. Some may be manual reset, which would disable you permanently if you don't know to push the reset button.
If you have a newer, fancier model with updraft fan, your controller may be sensing failure there and refusing to cycle further; manually test that like any other component.
Does yours have a CO or other gas sensor? I don't know if any do have those, but it's not beyond imagining; fake the signal there if so to absolve that.
If all those sub components work but it doesn't cycle, it's your controller, which is a replaceable (if ridiculously overpriced) module. (Mine contain maybe $5 of components, list price for $250. I'm in the wrong business.)
And if it passes all those tests and still won't run, call an exorcist.
Jim S
Jan 1, 2017, 9:42:37 AM1/1/17
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You can jumper the wire for heat right at the furnace to 24V which eliminates the thermostat. Then carefully observe the sequence of events with the door open (there is a switch that needs to be held down that the door normally holds). If it has a draft inducer (pulls the combustion gas through the furnace) that should start first. A pressure switch checks that it is operating. Then the gas valve opens and the hot surface or spark igniter lights the gas. You should be able to see the spark or glowing red hot surface if you get at the right angle. Once the burner is on for a short time the main fan should come on.
Does the main fan run when the thermostat is set to fan on (runs the fan even when the furnace/ac is off)?
How old is the furnace?
Many current ones have an LED that flashes or other indication of faults. You count the number of flashes or some such and then look up the code in the manual.
Does the main fan run when the thermostat is set to fan on (runs the fan even when the furnace/ac is off)?
How old is the furnace?
Many current ones have an LED that flashes or other indication of faults. You count the number of flashes or some such and then look up the code in the manual.
Brad Tissi
Jan 1, 2017, 1:45:17 PM1/1/17
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The furnace is only about 10 years old and it's all electric.
I've not been able to find a reset switch and I'm assuming that it doesn't have one at this point.
I'm wondering if Z1 might be the issue on the board.
Replacement board and transformer are on their way, but won't be here until Wed. Hopefully something can be done before then.
Jim S
Jan 1, 2017, 2:39:55 PM1/1/17
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I had thought it was a gas furnace - pretty much everything I said doesn't apply...
Z1 is a zener diode. Why do you suspect Z1? I don't see any signs of overheating or damage (still possible it's bad but less likely). The red around it is a marking on the PC board not damage. If the heatpump is not working then the backup electric heat should be coming on (after some delay). Might be a bad relay. Should be fairly easy to measure coil voltage and then voltage on the contacts to verify the contacts are making contact.
Most modern thermostats for AC or heatpumps have a delay built in that prevents the compressor from trying to come on for about 10-15 minutes after power up since they won't start if pressure has already been built up. That could be causing some trouble in testing.
Z1 is a zener diode. Why do you suspect Z1? I don't see any signs of overheating or damage (still possible it's bad but less likely). The red around it is a marking on the PC board not damage. If the heatpump is not working then the backup electric heat should be coming on (after some delay). Might be a bad relay. Should be fairly easy to measure coil voltage and then voltage on the contacts to verify the contacts are making contact.
Most modern thermostats for AC or heatpumps have a delay built in that prevents the compressor from trying to come on for about 10-15 minutes after power up since they won't start if pressure has already been built up. That could be causing some trouble in testing.
Brad Tissi
Jan 2, 2017, 2:19:02 PM1/2/17
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Z1 was just the only component that had something odd about it. It isn't burnt or anything obvious, but that's about all that I had to go on.
Jumping 24v didn't do anything either. I'm beginning to suspect the relay at this point.
Brad Tissi
Apr 27, 2017, 2:04:19 PM4/27/17
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I should probably update this thread.
In the end, I made a bad assumption to start checking electrical at the transformer and work my way down. As it turned out, the original problem was one of the two breakers.
It was losing voltage across it a bit more with each flip while checking everything, which only made matters worse and with confusing results.
SC Electric had a replacement in stock (bolt-on style), which took care of that issue, but in my eagerness to test it out, I forgot to put back the smaller transformer. I had it wired to give 24VAC apparently on the lower source voltage, which when corrected, meant that there was some higher voltage getting to the fan control board.
So, fuse and cap burnt, I switched to the replacement board that I had already gotten thanks to ebay. Well, heat worked, but I had no manual fan control, which meant that the AC compressor would have run without a blower come warmer weather.
Okay, that can wait a week or two...a month later, I finally getting around to testing a theory that both the now-repaired original control board and the refurbished ebay board both have fused relays. What are the chances that both are somehow fused? Apparently pretty good.
Solder in a new relay on the original franken-board, and voila, everything works.
Do the same to the replacement board with the same positive results.
Welp, that was fun. Now I know this furnace and AC like the back of my hand, and have spare transformers as well as a second fan control board.
Thank you for all the help.
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