If you're safe with a VOM, here's the technique:
Where the BX cable comes in on top (right over
the inducer fan), it ties into the furnace inside
the small box inside the case of the furnace. You
can get into the small box, and check for polarity
and if the ground is connected.
I hesitate to suggest people open up safety boxes
and work with live power, some folks can't do that
safely. Prefer not to go into a lot of detail on
an open forum.
Open ground can cause problems, also.
Christopher A. Young
Learn about Jesus
trader_4 wrote, on Sat, 20 Dec 2014 05:37:54 -0800:
I turned off the power.
Put the covers back on.
Turned the power back on.
Waited about 20 minutes.
Turned it off for a few minutes.
Turned it back on.
Set the heat to HOLD at 80 degrees.
The blinking lights don't seem to have changed.
Here is the latest blinking light - which is odd as it stumbles
at 24 seconds, but I don't know what to make of that anomaly.
Tony Hwang wrote, on Sat, 20 Dec 2014 19:41:51 -0700:
I found where to get manuals but I can't find the exact model:
The model is a Bryant 373LAV024070 (AGJA).
The closest Bryant PDF manual I can find is:
373LAV 376CAV Downflow/Horizontal and 383KAV 395CAV Upflow Gas Furnace
383KAV Upflow Gas Furnace 373LAV Downflow Horizontal Gas Furnace
I'll call Bryant on Monday to figure out why I can't find the
exact model in the lists of documents:
800-428-4326 from 5:00am-2:00pm (Pacific) weekdays.
On Monday, December 22, 2014 6:32:55 AM UTC-5, Danny D. wrote:
Then it's nothing to do with it failing to ignite, overheating, gas
supply, etc. It;'s detecting something wrong with just the application
of power, without it even having a call for heat, trying to fire, etc.
Could be some sensor input is lacking, but then you'd think it would be
flashing a code that was in the table. Given what it's doing, my first
suspicion would be that it's a bad control board. Did you put a meter on
it when power is first applied, verified that it has 120V, ground is OK,
Stormin Mormon wrote, on Mon, 22 Dec 2014 07:50:33 -0500:
I stuck my hands in there, and the opening is above.
Plus, it used to work, and nobody has touched it since.
It *was* embarrassing when I saw that cruddy filter.
I almost didn't want to post a picture before I cleaned it.
According to the manual, there is supposedly a "v-shaped" set
of filters at the blower itself, but I haven't been able to
find them yet.
Stormin Mormon wrote, on Mon, 22 Dec 2014 07:50:33 -0500:
I found that blower you show after looking at the manual:
Mine is apparently a "downflow" horizontal model (373LAV), whatever
"downflow" means (as opposed to "upflow" types).
I guess that this means that the air flows "down", which, in the
case of my furnace, is sidewise, I presume to the right (but I'm
just guessing since the direction of airflow isn't described in
I called Bryant (at 800-428-4326x3), who confirmed the furnace
is a series G, which was built within the last 15 years, and
actually, based on the serial number, was built in 1999.
They will be sending me more detailed manuals, which I will
let you know when I get them.
Some applications like mobile homes, the air
flows from top to bottom (downflow). Many houses
have furnace in the cellar, and are up flow,
meaning the conditioned air blows out the top.
In the horizontal, doesn't make much difference.
Anyhow, good luck and skill. I hesitate to do
much electrical coaching on an open list like
trader_4 wrote, on Mon, 22 Dec 2014 03:57:10 -0800:
I agree with you that the first thing I need to test is power and
The sad thing is that I don't have a clue how to test that, as only
once before did I ever troubleshoot a furnace. I don't even remember
if it's AC or DC control inputs. Nor which color wires do what
(although I do remember that it's a standard, so, I can look that up).
I just received from Bryant two more PDF manuals, in addition to the
sparse 12-page 373 LAV Series G "User's Information Manual" that
I had already found, namely:
a. Installation Start-up, and Operating Instructions (24 pages)
b. Service and Maintenance Procedures (16 pages)
I can convert the PDF to JPEG and then post the JPG so you can read
them, but is there a way to just post the PDF for you to view them
to help interpret them?
On Monday, December 22, 2014 9:30:56 AM UTC-5, Danny D. wrote:
The thing is constantly flashing, which according to the table, is
polarity reversed. That's virtually impossible, but there could be
something wrong with the incoming AC. To test it with a VOM:
turn off power, usually via turning off the red safety toggle switch
that's mounted near the furnace.
get access to the incoming AC, remove wire nuts from hot and neutral,
but leave wires twisted together
make sure wires are in the air, not touching anything
then turn power switch back on
with VOM check for
120V from hot (black) to neutral (white).
120V from hot to ground (that tells you it's not reversed polarity and
that the ground is likely OK.
0V from neutral to ground
Then turn off power and put it back together.
You could also do it easier without removing wire nuts if you
can find hot/neutral identified on the control board. You could just
probe it there.
If you're unsure about any of that, or basic electric safety,
I agree with Stormin. Either call a friend in who is, or just call for service.
Besides, I'd bet 99% that nothing is wrong with the power.
Stormin Mormon wrote, on Mon, 22 Dec 2014 07:54:59 -0500:
I'm perfectly fine with 120/220V and can easily work with my
Fluke 75 on the furnace. I just need to know what to check,
bearing in mind that it's not at first obvious where the power
comes in yet.
I can't imagine that the power polarity has reversed, on its own,
but, as you note, I should check it (since the flashing is hard
to understand and one interpretation of the flashes might be that
the power polarity is reversed).
Of course, that only matters for DC, right?
So I'd need to know *where* the DC is coming from, since the line
voltage is AC (yes, I know a neutral isn't the same as a hot, nor
even the same as a ground, but, in terms of polarity, switching
a neutral with a hot shouldn't matter for AC motors or step-down
transformers (which I presume exist near the circuit board).
I have no problem whatsoever working around power.
Stormin Mormon wrote, on Mon, 22 Dec 2014 09:38:59 -0500:
Heh heh ...
I know how to use a DMM as well as anyone here knows how to
use one. I have had Simpson (analog) ammeters and voltmeters
since I was a young teen, when I was making my own resistance
testing equipment long before consumer DMMs were common.
My Fluke 75 is a good meter, which I've had for something
like 30 years. So, *using* a meter isn't at all a problem.
The problem is knowing what measurements to take.
To that end, this control board summary is a start:
As is this wiring control schematic:
And, of course, as is the overall furnace circuit schematic:
All of which I'm new to, but, which I will print and pore over
to see what basic control and power inputs to test with my
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