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Furnace Inducer Motor Troubleshooting! Top 8 Problems!


Hey guys this is AC Service Tech and
today what we’re going over is the top eight reasons why an inducer motor on a
natural gas or propane gas furnace does not seem to be working. The inducer
motors job is to actually push the exhaust gases out through the exhaust
and it actually sucks in the intake right from here through the heat
exchanger and through the burner tube assemblies. So the inducer motor is the
first thing that ends up being turned on by either the relays or the control
board for the heat sequence to turn on. So this needs to turn on first and then
it’s proven by a pressure switch. A pressure switch could look something
like this or like this but basically they are
sensing the negative pressure coming from either the inducer motor housing or
through a condensate drain. In order to determine that this is actually working in that there’s no clogs. Reason number one could be that the signal wire from the thermostat is not making it back to the control board in order for the
control board to tell the inducer motor to turn on. So the way that we confirm if
the control board is actually receiving this signal back from the thermostat is
we have R coming to the thermostat and it connects to W and then W comes back
as the 24 volt wire. So this is the hot wire and we can check it between white
and common. So we have our multimeter set to volts AC and right now we’ll go ahead
and check and we see that we are reading nothing. So we got point zero three three
volts and we are set on heat and the thermostat is calling. It says we want it
set to 81 and it’s 54 in the room so it definitely should be calling at this
point. You can see that we actually have 24 volts from R to C right here and
what should be happening is the R and W should be touching and we should be
getting 27 volts here and we’re not. In this case you’d either have a problem
with your thermostat itself or the thermostat wires and the way to
determine if it’s the thermostat face is what you could do is take the face off
and then jumper from W to R and see if you have the same problem. So if
we jumpered from W to R then that should tell heat to turn on. And the first thing
that happens in the sequence of operation for the furnace is that the
control board is going to send power to the inducer motor. So now we can go ahead and check our voltage. We can check from W to C. And you see that now we have 27
volts. That tells you that the thermostat face is the problem. If we actually took
the face off and we jumpered inside the thermostat face from R to W then you
know that this was the problem. So if you don’t have mag jumpers what you could do
is turn the power off and then you could jump the R and the W together with a
wire nut. And then you can go ahead and check inside your furnace at your
control board for W to C and you see that we have 27 volts right now. So this
is problem number two. Once you verified that you have 24 volts from W to C and
actually it’s anywhere from 24 to 29 volts, so once you’ve verified that you
have a signaled calling for heat you want to go ahead and check for your
inducer motor wiring. You want to make sure that you are finding the right
wires here and you’re following it from the inducer motor back to the control
board. In this case I’ve already disconnected the wire and I have the
probes in and I’m checking for voltage. So you see that the control board is not
sending the 120 volts that it needs to the inducer motor. So in this case this
would actually be a board problem. Any time you think it’s a board problem you
want to make sure that you’re not quick to condemn the board. It’s actually one
of these relays right in here that would end up closing allowing the
120 volts to go through but you know there could be another issue such as a
sensor or something like that but in that case you’ll notice that the blower
motor does not want to turn off so just make sure your limit sensors are working
properly and that you don’t have a lower limit
gas switch and a propane furnace. Things like that before you end up condemning the board. In reference to checking ECM variable speed inducer motors, what we need to do is actually access the troubleshooting guide for that model
number furnace and typically on the side right here there’s gonna be a connector
that you’re gonna have to check DC voltage readings off of. Alright so
you’re gonna follow with the troubleshooting guide
it says from that manufacturer and you’re going to see the DC voltage
values changing. Problem number three. What could happen is if you have a 120
volt or 240 volt inducer motor and your capacitor could be bad. So this
is actually a capacitor this little block right here. So make sure that you
have the power off, you’re going to go ahead and disconnect the electrical
connections off of there. You’re going to go ahead and short out the terminals
just like this. And this one says 3uf and 250 volts. So we’re gonna go ahead and
test this with a multimeter. We’re gonna turn this on to micro farads. So we’re
gonna have to hit this select button and then we’re gonna go ahead and check our
micro farad reading. We’re gonna hold this in and you want to give it possibly
up to even you know 15 seconds or so just in order to make sure that this is
correct. So you see our reading right here is 2.3 uF. So this capacitor is
actually more than 5% off. So you can replace this with a like stock capacitor that looks like this a capacitor that’s bigger that looks like
this. The difference between these two is the voltage right here. This is 250 volts
and this one’s 370 volts and it has to do with how much insulation is inside
the capacitor. You have to replace this 3 UF or 3 MFD with the same size so this
one won’t work because this is a 5 MFD capacitor but if you did have one that
would say a 3 MFD that looked like this you could replace this capacitor with it.
This capacitor has to be installed on typically its brown wires or one brown
wire and one white wire and it has to be in place for the motor to even be able
to start up and also to run. So number four, the actual inducer motor bearings could be seized. So in this case we can actually get into this shaft right here
in order to try to spin it and we see that that one’s moving freely.
But you can get into one and you can kind of feel it it’s really really stuck
and once you get it spinning then it seems to be working. A lot of times it’s
upon an initial startup of the furnace for the first time in heating season. A
lot other times it might just be in the middle of the heating season. You can
tell this one is very easy in order to make sure that the inducer motor is
spinning freely. On one such as this once again just make sure the power is off
and you can’t get into here so you just take your your thermostat screwdriver
and see if you can get it to spin that way. If you notice that a motor has
actual ports on it for oil those are not sealed bearings and those are the ones
that end up needing to be oiled. If it ran out of oil and the bearings are
seized then the damage has already occurred and that would be one that you
would end up recommending replacing. But how you add the oil in is you just go
ahead and take this tube right here and you put it right into the hole and then
you go ahead and squeeze here your zoom spout until you have this basically
overflowing. You don’t want to overflow crazy amount but you do want to get
enough oil in to make sure that you have that whole reservoir filled up. So we
should be pretty darn close right there. Now just you know just because you see
these ports right here does not mean that this is a non sealed bearing that
needs to be oiled. You can actually look inside and there is no trough for the oil and it actually says sealed ball bearings. So these outer casings of
the inducer motor are are made for a multitude of different model number
blower motors. So this one this one happens to be one that has a sealed ball
bearing and make sure that you do not put any oil down inside that hole for
sure. This is problem number five and this inducer motor was out of a package
unit and you can see that this one has some play in it. It actually moves back
and forth like this and the problem with that was that the inducer wheel was
binding on the edge by the heat exchanger and that was a problem. And
then the inducer motor was not turning on it was actually just getting stuck.
Alright so that’s that’s something that could happen or
debris can be stuck in here maybe from a bird’s nest and that’s not allowing the
motor to turn on. This is problem number six. In this case once again the inducer
motors out of a package unit and the problem with this one was that the
inducer wheel actually has fallen off completely due to rot. Alright so it’s
rusting and just rotting the metal right there and it’s coming completely off. You
can have something like this that’s metal but you can even have plastic ones
where these actually all fall apart on the inside and then jam the wheel and
then basically you need to replace this or replace the entire housing. So problem
number seven could be that the inducer motor actually is running but you’re
having some problem with proving that this is running with the pressure switch.
So the sequence of operation for heat goes with the inducer motor turning on
first, the pressure switch proving that the inducer motor is working in that and
that there’s no clogs, and then after that the ignition source gets turned on.
And what could be happening is this pressure switch could not be proving
that this is operating and I like to typically measure the pressure switch
out with the SD man 6. Alright so this tool right here is
very very useful because you can actually isolate the pressure switch
completely away from the system just to make sure that this is correct or not
correct. As well if you were going to go ahead and blow out these lines make sure
that you disconnect them from the pressure switch before you put any
pressure on them. Alright so then you can blow these out you could have a problem
if the pressure switch tests good. You could have a problem with maybe your
condensate trap for your 90% efficient furnace maybe that’s clogged or maybe
the drain piping is clogged or maybe the tubing like this tubing right here is
clogged or maybe you have a clog in your exhaust or clogging your intake. Possibly
maybe the heat exchanger is clogged and if that’s the case, that’s a very serious
situation you want to make sure that you go ahead and verify if that is clogged. And then problem number eight could be that the actual inducer motor may be
burned out. So you could do a quick sniff test in order to smell if the windings
are burnt out and then in reference to testing it with resistance with your
multimeter, you make sure that your furnace is off,
you unplug the motor, and unplug the capacitor, and your first check will be
on ground. So you see I have my one probe and ground. You never put your test probes
in this part because you don’t want to oblong the connections you always put
them in the back part. So you can check right here and we’re checking for a
resistance values between ground and common, you see that we have none right
there, “OL” over limit. We see that we have
right here on ground to hot there’s no problem, and just so you know when you
have the two wires going to the capacitor the one that’s brown
and white, that one’s actually touching the white wire inside of this 120 volt
inducer motor right here. So we already tested the white so we know that that is
no problem. You see that we once again have OL and we’ll check this one
anyway. And you see that we have OL. So we know that the windings did not
short against the ground frame and we can see that our ground is intact another
way to do this is actually to try to take, you know this is all painted, but
you want to take a your ground connection right here at your motor. The
next test that we’ll do is we’ll just check the windings and we’ll go from
common to hot. And you see that we have 34 ohms or resistance. We’ll get the same
reading if we go from hot to this capacitor wire with the white on it.
Should have about 34 ohms of resistance. The other one said 34.7 this one says
34.6 ohms and now we’ll go ahead and check from hot to the other
capacitor wire. And you see that we’re reading 117 ohms. And now I’ll go ahead
and check from common to hot. Basically what we’re making sure of is
that we don’t have 0.0 ohms or resistance and that we don’t have OL because OL would mean that the windings are burnt apart and 0.0 ohms would mean that the windings are all melted together. And you see that
we have 152.3 ohms. So this motor checks out good in reference to the resistance readings. If
this inducement motor was bad we would probably smell the burnt windings and
we’d probably also have a OL reading across the windings. And if you
look for any of the tools and supplies used this video I have them all linked
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Bernard Jenkins

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