Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So I
swapped thermostats. It worked again for a couple of days, and then failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but it
SEEMS that the furnace is shutting off 24v when heat is called. It's not
the blower though, because if I just turn the fan on (from the thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat line
directly, and the heat didn't come on, but I'm not sure if that's the proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

Max Metral wrote:

but it SEEMS that the furnace is shutting off 24v when heat is called.

Let me make a guess, You wired one of W, W2 to C?

No, not this time.

"Brian" wrote in message
oups.com...

Max Metral wrote:

but it SEEMS that the furnace is shutting off 24v when heat is called.

Let me make a guess, You wired one of W, W2 to C?

I guess you gave up on those pricks in alt.hvac, eh?

They were indeed remarkably rude. At least most of them, a couple were
helpful.

Anyhow, the main question has now become, if my digital (i.e. needs power)
thermostat says it only requires the following leads connected:

R - 24vac
G - fan
W - heat
Y - cool

Where does it get power when it demands heat, thus shorting (?) G and W to
R? I would assume (standard decomposition of assume applies) that it gets
it from Y staying at ground, and perhaps that's where the fault has
occurred. If not, where else can it pull the power?

wrote in message
ps.com...
I guess you gave up on those pricks in alt.hvac, eh?

Where does a lighted doorbell button get its power from? It only has
two wires and it lights without ringing the doorbell.

Mike

Most digital thermostats require a ground (24V common) If you don't
have one the batteries will power it for a few days, then it will die.
Get a mercury non programmable thermostat or run at least a 5-wire
cable and hook up 24V common.

You may be able to get your system to work with a power robbing
thermostat. Those will work without a common. They use the Y & W as a
ground (common) when heat or cool is off, using just a trickle of
current to power the thermostat. Power robbing thermostats usually
don't have back lit displays, as that requires more power than they can
steal.

Stretch

wrote in message
oups.com...
Where does a lighted doorbell button get its power from? It only has
two wires and it lights without ringing the doorbell.

Mike

The light bulb is in series with the transformer and the door bell coil.
The bulb does not draw enough current that would pull in the door bell
coil. When you press the button, the bulb is shorted out and the only thing
in the circuit with the transformer is the coil.

If the thermostat connects R to W when it calls for heat that's not the
same as shorting it to ground! A digital stat will still get power. If a
call for heat is grounding out the 24V then presumably something is wired
wrong, the stat is defective or something is wrong at the furnace end.

On Sun, 18 Dec 2005 19:14:23 -0500, Max Metral wrote:
They were indeed remarkably rude. At least most of them, a couple were
helpful.

Anyhow, the main question has now become, if my digital (i.e. needs power)
thermostat says it only requires the following leads connected:

R - 24vac
G - fan
W - heat
Y - cool

Where does it get power when it demands heat, thus shorting (?) G and W to
R? I would assume (standard decomposition of assume applies) that it gets
it from Y staying at ground, and perhaps that's where the fault has
occurred. If not, where else can it pull the power?

If the thermostat does not have batteries, you may need to connect the
other side of the transformer to C (common). Some thermostats I got for
our warehouse need that if you want to use them without the batteries
(although I think that is just mentioned, not shown in wiring diagram).

On Sun, 18 Dec 2005 19:14:23 -0500, "Max Metral"
wrote:

They were indeed remarkably rude. At least most of them, a couple were
helpful.

Anyhow, the main question has now become, if my digital (i.e. needs power)
thermostat says it only requires the following leads connected:

R - 24vac
G - fan
W - heat
Y - cool

Where does it get power when it demands heat, thus shorting (?) G and W to
R?

Is this a question with a built -in answer!

The way you have your question, after the chart, makes me think you
don't underwstand.

First, I'm pretty sure the thermostat gets its power from the same
source when it is "calling for heat" as any other time.**

Assuming your colors, when you turn the fan to On, it's going to
connect the R to the G, so the fan terminal back at the furnace gets
24 volts.

But when you turn the thermostat switch to Heat, and it is cold enough
to call for heat, it's going to connect the R to the W, so that the
Heat terminal back at the furnace gets 24 volts. Unless the fan
switch is on fan (and if that is the case, the fan is already running)
it's not going to supply 24 volts to the G, because that would keep
the fan running regardless of what the heating circuit wants, and the
heating circuits in the last 30 years or more have wants. They want
the fan OFF until the air in the furnace is hot, and they want the fan
ON until the air in the furnace has cooled off a lot. The heat
circuit is in charge of the entire heat functioning, including the
fan. The Fan is directly controlled by the thermostat, only when the
Fan/Auto switch is set on Fan.

** In my case, that is the furnace with battery backup. I know that
because I haven't replaced the battery in more than a decade, and
indeed when I turn off the power to the furnace, the thermostat
forgets what time it is. So I know the furnace powers it, and I'm
sure the battery would also if it weren't dead. But I get the
impression that not all thermostats work the same way. (I only depend
on the battery to keep the day and time. The temperature and setback
times are set by mechanical multi-segment slide switches.)

I would assume (standard decomposition of assume applies) that it gets
it from Y staying at ground, and perhaps that's where the fault has
occurred. If not, where else can it pull the power?

wrote in message
ups.com...
I guess you gave up on those pricks in alt.hvac, eh?




Remove NOPSAM to email me. Please let
me know if you have posted also.

mm wrote:
On Sun, 18 Dec 2005 19:14:23 -0500, "Max Metral"
wrote:


They were indeed remarkably rude. At least most of them, a couple were
helpful.

Anyhow, the main question has now become, if my digital (i.e. needs power)
thermostat says it only requires the following leads connected:

R - 24vac
G - fan
W - heat
Y - cool

Where does it get power when it demands heat, thus shorting (?) G and W to
R?


Is this a question with a built -in answer!

The way you have your question, after the chart, makes me think you
don't underwstand.

First, I'm pretty sure the thermostat gets its power from the same
source when it is "calling for heat" as any other time.**

Assuming your colors, when you turn the fan to On, it's going to
connect the R to the G, so the fan terminal back at the furnace gets
24 volts.

But when you turn the thermostat switch to Heat, and it is cold enough
to call for heat, it's going to connect the R to the W, so that the
Heat terminal back at the furnace gets 24 volts. Unless the fan
switch is on fan (and if that is the case, the fan is already running)
it's not going to supply 24 volts to the G, because that would keep
the fan running regardless of what the heating circuit wants, and the
heating circuits in the last 30 years or more have wants. They want
the fan OFF until the air in the furnace is hot, and they want the fan
ON until the air in the furnace has cooled off a lot. The heat
circuit is in charge of the entire heat functioning, including the
fan. The Fan is directly controlled by the thermostat, only when the
Fan/Auto switch is set on Fan.

** In my case, that is the furnace with battery backup. I know that
because I haven't replaced the battery in more than a decade, and
indeed when I turn off the power to the furnace, the thermostat
forgets what time it is. So I know the furnace powers it, and I'm
sure the battery would also if it weren't dead. But I get the
impression that not all thermostats work the same way. (I only depend
on the battery to keep the day and time. The temperature and setback
times are set by mechanical multi-segment slide switches.)


I would assume (standard decomposition of assume applies) that it gets
it from Y staying at ground, and perhaps that's where the fault has
occurred. If not, where else can it pull the power?


wrote in message
oups.com...

I guess you gave up on those pricks in alt.hvac, eh?




Remove NOPSAM to email me. Please let
me know if you have posted also.
Hi,
24V is coming from a step down transformer. Battery back up for 'stat is
to keep the program settings. As long as main power breaker to furnace
is on, 24V should be present. It's called logic sequence control power.
If it goes missing, something is shorting it out or the transformer is
bad. Or sosmething is loose.
Tony

Max Metral wrote:

Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So I
swapped thermostats. It worked again for a couple of days, and then failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but it
SEEMS that the furnace is shutting off 24v when heat is called. It's not
the blower though, because if I just turn the fan on (from the thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat line
directly, and the heat didn't come on, but I'm not sure if that's the proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

If your thermostat takes batteries then replace them. A battery powered
t-stat with weak batteries will drop out when it attempts to bring in
heating or cooling, having enough power for the display, but not enough
for the internal relay circuits.

If your thermostat doesn't take batteries then it is a power stealing
stat, using Y to tap into common back through the compressor contactor.
Depending upon model Y may or may not go directly to the compressor
contactor--it may go instead through an electronic circuit on a main
control board. This type of system may require that a resistor be wired
across Y and C in the unit in order to provide a low resistance path
from Y to C. This type of stat usually comes with a large ceramic
resistor packaged with it.

There are also power stealing stats that also use batteries for backup.
The batteries in these are only provided to hold program and temp
settings in the event of a power failure.

Barring all of this it may be that your unit is shorted somewhere
internally which could cause power to drop at the transformer, and thus
from the t-stat when it calls for heat.

hvacrmedic

So, it turns out the therm IS a power stealing therm. What's strange is
that when EVERYTHING is off, I still have 0V across Y and R**, so of course
the therm has nowhere to steal power from when R and W are connected. The
obvious fix is to connect C (I don't have a labeled C on the furnace board,
will a screw terminal on the chassis do?) But the most confusing part is
that this has worked for years, and now suddenly stopped. So I'm not sure
if that means something has gone wrong with the unit and I should tread
carefully. I'm also not sure whether this is just a little reminder that a
15 year old furnace should be scrapped.

** In truth, it's not 0, it's some barely readable amount. The meter moves,
but hardly.

"RP" wrote in message
et...


Max Metral wrote:

Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So I
swapped thermostats. It worked again for a couple of days, and then
failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will
come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but it
SEEMS that the furnace is shutting off 24v when heat is called. It's not
the blower though, because if I just turn the fan on (from the
thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat line
directly, and the heat didn't come on, but I'm not sure if that's the
proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

If your thermostat takes batteries then replace them. A battery powered
t-stat with weak batteries will drop out when it attempts to bring in
heating or cooling, having enough power for the display, but not enough
for the internal relay circuits.

If your thermostat doesn't take batteries then it is a power stealing
stat, using Y to tap into common back through the compressor contactor.
Depending upon model Y may or may not go directly to the compressor
contactor--it may go instead through an electronic circuit on a main
control board. This type of system may require that a resistor be wired
across Y and C in the unit in order to provide a low resistance path from
Y to C. This type of stat usually comes with a large ceramic resistor
packaged with it.

There are also power stealing stats that also use batteries for backup.
The batteries in these are only provided to hold program and temp settings
in the event of a power failure.

Barring all of this it may be that your unit is shorted somewhere
internally which could cause power to drop at the transformer, and thus
from the t-stat when it calls for heat.

hvacrmedic

It's my understanding that there is no C on most wiring, because there
isn't a need for one. (Ungrounded light switches don't have a common
wire; they just connect the hot wire to the light.) All of the
appliances are grounded so you only need the power wire and a wire for
each device. Connecting R (24VAC) to a appliance's wire completes the
circuit and allows the appliance to run.

If it has worked for years then, yes, something has gone wrong. I
would verify the wiring and then call the furnace guy to fix the
problem.

Mike

Oh, and on a side note...

My mother's furnace behaved similarly years ago. The completely
incompetent LICENSED HVAC guys that installed her furnace didn't ground
it and it kept frying control boards. Fortunately, after their many
stupid attempts to fix it and subsequent complaints to the
manufacturer, Bryant sent their own techs out to fix it. And then
Bryant stopped those lamebrains from using their products again.

Mike

wrote:
It's my understanding that there is no C on most wiring, because there
isn't a need for one.

Your understanding needs updating. In a typical resi HVAC system the 24v
secondary from the transformer has a hot and a common. The common isn't
necessarily grounded, but it is called common because it is fed directly
to one side of every load. In some systems the common is also switched,
but it is understood by any tech that common (C) is the transformer leg
that is not fed to R on the t-stat. HTH.

hvacrmedic


(Ungrounded light switches don't have a common
wire; they just connect the hot wire to the light.) All of the
appliances are grounded so you only need the power wire and a wire for
each device. Connecting R (24VAC) to a appliance's wire completes the
circuit and allows the appliance to run.

If it has worked for years then, yes, something has gone wrong. I
would verify the wiring and then call the furnace guy to fix the
problem.

Mike

Max Metral wrote:

So, it turns out the therm IS a power stealing therm. What's strange is
that when EVERYTHING is off, I still have 0V across Y and R**, so of course
the therm has nowhere to steal power from when R and W are connected. The
obvious fix is to connect C (I don't have a labeled C on the furnace board,
will a screw terminal on the chassis do?) But the most confusing part is
that this has worked for years, and now suddenly stopped. So I'm not sure
if that means something has gone wrong with the unit and I should tread
carefully. I'm also not sure whether this is just a little reminder that a
15 year old furnace should be scrapped.

Call a tech.

hvacrmedic


** In truth, it's not 0, it's some barely readable amount. The meter moves,
but hardly.

"RP" wrote in message
et...


Max Metral wrote:


Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So I
swapped thermostats. It worked again for a couple of days, and then
failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will
come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but it
SEEMS that the furnace is shutting off 24v when heat is called. It's not
the blower though, because if I just turn the fan on (from the
thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat line
directly, and the heat didn't come on, but I'm not sure if that's the
proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

If your thermostat takes batteries then replace them. A battery powered
t-stat with weak batteries will drop out when it attempts to bring in
heating or cooling, having enough power for the display, but not enough
for the internal relay circuits.

If your thermostat doesn't take batteries then it is a power stealing
stat, using Y to tap into common back through the compressor contactor.
Depending upon model Y may or may not go directly to the compressor
contactor--it may go instead through an electronic circuit on a main
control board. This type of system may require that a resistor be wired
across Y and C in the unit in order to provide a low resistance path from
Y to C. This type of stat usually comes with a large ceramic resistor
packaged with it.

There are also power stealing stats that also use batteries for backup.
The batteries in these are only provided to hold program and temp settings
in the event of a power failure.

Barring all of this it may be that your unit is shorted somewhere
internally which could cause power to drop at the transformer, and thus
from the t-stat when it calls for heat.

hvacrmedic

In article .com,
wrote:
Where does a lighted doorbell button get its power from? It only has
two wires and it lights without ringing the doorbell.

The transformer that supplies the doorbell supplies the light. The
current drain for the light also flows thru the bell, but is much lower
than the current needed to ring the bell. When you press the button,
the light is shorted and the current rises to enough to ring the bell.

--
Rich Greenberg Marietta, GA, USA richgr atsign panix.com + 1 770 321 6507
Eastern time. N6LRT I speak for myself & my dogs only. VM'er since CP-67
Canines:Val, Red & Shasta (RIP),Red, husky Owner:Chinook-L
Atlanta Siberian Husky Rescue. www.panix.com/~richgr/ Asst Owner:Sibernet-L

Yes, it was a dangerous mistake. I should have said common instead of
ground. My point was that you don't need both sides of a power supply,
because you only switch one. Thanks.

Mike

On Sun, 18 Dec 2005 19:14:23 -0500, "Max Metral"
wrote:

They were indeed remarkably rude. At least most of them, a couple were
helpful.

Anyhow, the main question has now become, if my digital (i.e. needs power)
thermostat says it only requires the following leads connected:

R - 24vac
G - fan
W - heat
Y - cool

Where does it get power when it demands heat, thus shorting (?) G and W to
R?

Some furnaces switch the fan internally when heat is being used, and
require only R & W to be shorted.

I would assume (standard decomposition of assume applies) that it gets
it from Y staying at ground,

I would assume Y would be connected to a relay coil for the AC
compressor, and would be open not ground. It may be possible to use it
for a ground, as long as the current drain in very low.

and perhaps that's where the fault has
occurred. If not, where else can it pull the power?


The first electronic thermostat I installed required an additional
connection, which required running a 5th wire. The contact point
wasn't hard to find, since I had a wiring diagram for that furnace. I
think it was labeled "C" (24VAC common). The thermostat I have now (in
a different house), uses a separate power supply (wall wart).

wrote in message
ups.com...
I guess you gave up on those pricks in alt.hvac, eh?


--
6 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On 18 Dec 2005 17:07:46 -0800, wrote:

Where does a lighted doorbell button get its power from? It only has
two wires and it lights without ringing the doorbell.

Mike

When a doorbell button is NOT being pushed, there will be 16VAC (or
somewhat higher) across the contacts. A bulb could be connected across
here. It would be in series with the bell, but this would still work
if the bulb has a high enough resistance that the current would still
be too little to ring the bell (and many doorbells are actually
chimes, that make sound only when the current starts or stops, not
when it's steady).

BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?
--
6 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On Mon, 19 Dec 2005 07:11:14 GMT, Tony Hwang wrote:

mm wrote:
On Sun, 18 Dec 2005 19:14:23 -0500, "Max Metral"
wrote:


They were indeed remarkably rude. At least most of them, a couple were
helpful.

Anyhow, the main question has now become, if my digital (i.e. needs power)
thermostat says it only requires the following leads connected:

R - 24vac
G - fan
W - heat
Y - cool

Where does it get power when it demands heat, thus shorting (?) G and W to
R?


Is this a question with a built -in answer!

The way you have your question, after the chart, makes me think you
don't underwstand.

First, I'm pretty sure the thermostat gets its power from the same
source when it is "calling for heat" as any other time.**

Assuming your colors, when you turn the fan to On, it's going to
connect the R to the G, so the fan terminal back at the furnace gets
24 volts.

But when you turn the thermostat switch to Heat, and it is cold enough
to call for heat, it's going to connect the R to the W, so that the
Heat terminal back at the furnace gets 24 volts. Unless the fan
switch is on fan (and if that is the case, the fan is already running)
it's not going to supply 24 volts to the G, because that would keep
the fan running regardless of what the heating circuit wants, and the
heating circuits in the last 30 years or more have wants. They want
the fan OFF until the air in the furnace is hot, and they want the fan
ON until the air in the furnace has cooled off a lot. The heat
circuit is in charge of the entire heat functioning, including the
fan. The Fan is directly controlled by the thermostat, only when the
Fan/Auto switch is set on Fan.

** In my case, that is the furnace with battery backup. I know that
because I haven't replaced the battery in more than a decade, and
indeed when I turn off the power to the furnace, the thermostat
forgets what time it is. So I know the furnace powers it, and I'm
sure the battery would also if it weren't dead. But I get the
impression that not all thermostats work the same way. (I only depend
on the battery to keep the day and time. The temperature and setback
times are set by mechanical multi-segment slide switches.)


I would assume (standard decomposition of assume applies) that it gets
it from Y staying at ground, and perhaps that's where the fault has
occurred. If not, where else can it pull the power?


wrote in message
roups.com...

I guess you gave up on those pricks in alt.hvac, eh?




Remove NOPSAM to email me. Please let
me know if you have posted also.
Hi,
24V is coming from a step down transformer. Battery back up for 'stat is
to keep the program settings. As long as main power breaker to furnace
is on, 24V should be present. It's called logic sequence control power.
If it goes missing, something is shorting it out or the transformer is
bad. Or sosmething is loose.
Tony

On at least one furnace I've seen, the overheat switch would cut off
the 24V. This disables the gas valve and fan relay. The fan relay (the
one associated with heat, not "fan on" from thermostat) controls the
fan through the NC (normally closed) contact, so the fan runs
constantly in this case.
--
6 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

On Mon, 19 Dec 2005 09:37:45 -0500, "Max Metral"
wrote:

So, it turns out the therm IS a power stealing therm. What's strange is
that when EVERYTHING is off, I still have 0V across Y and R**, so of course
the therm has nowhere to steal power from when R and W are connected. The
obvious fix is to connect C (I don't have a labeled C on the furnace board,
will a screw terminal on the chassis do?)

Do you have a wiring diagram? It would show what the other side of the
24V transformer secondary is connected to.

If this furnace is connected to (or can be connected to) air
conditioning, there should be a C connection to go to the compressor.

But the most confusing part is
that this has worked for years, and now suddenly stopped. So I'm not sure
if that means something has gone wrong with the unit and I should tread
carefully. I'm also not sure whether this is just a little reminder that a
15 year old furnace should be scrapped.

** In truth, it's not 0, it's some barely readable amount. The meter moves,
but hardly.

"RP" wrote in message
news:y_2dnSizw4KZ9TvenZ2dnUVZ_sGdnZ2d@centurytel. net...


Max Metral wrote:

Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So I
swapped thermostats. It worked again for a couple of days, and then
failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will
come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but it
SEEMS that the furnace is shutting off 24v when heat is called. It's not
the blower though, because if I just turn the fan on (from the
thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat line
directly, and the heat didn't come on, but I'm not sure if that's the
proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

If your thermostat takes batteries then replace them. A battery powered
t-stat with weak batteries will drop out when it attempts to bring in
heating or cooling, having enough power for the display, but not enough
for the internal relay circuits.

If your thermostat doesn't take batteries then it is a power stealing
stat, using Y to tap into common back through the compressor contactor.
Depending upon model Y may or may not go directly to the compressor
contactor--it may go instead through an electronic circuit on a main
control board. This type of system may require that a resistor be wired
across Y and C in the unit in order to provide a low resistance path from
Y to C. This type of stat usually comes with a large ceramic resistor
packaged with it.

There are also power stealing stats that also use batteries for backup.
The batteries in these are only provided to hold program and temp settings
in the event of a power failure.

Barring all of this it may be that your unit is shorted somewhere
internally which could cause power to drop at the transformer, and thus
from the t-stat when it calls for heat.

hvacrmedic



--
6 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

Well, the uncertainty about why this happened after two working heating
seasons will be a great unanswered question in my life. (ok, well, not that
great) BUT, the problem is solved.

So, as suspected, the digital therm was simply losing access to power when
it routed R to W. The additional variable that I didn't realize is that
there's a summer/winter hard switch on the furnace. I assumed that normally
I had switched this to winter in the past. However, with meter in hand if
the switch is on summer, I measure 24VAC across R and Y. If the switch is
on summer, I measure 0VAC. I don't understand exactly what this switch does
that other than I suppose forcibly disabling the compressor. But given this
fact, there's no way for the therm to steal power when it requests heat, and
it shuts off.

My only explanation for previous success is that perhaps I forgot to switch
that to winter in the past. I suppose maybe that switch does something more
complex, which USED to leave Y at ground but doesn't anymore. It's also a
remote possibility that the power stealing can work by stealing from the fan
input, and that in my reconfiguring the therms, I reset it to request fan
and heat simultaneously thus killing 24VAC on G.

In any case, the solution was simple, run a dedicated C. That was sort of
the obvious first fix, but it just concerned me why it was a problem now.

I'll use the money I saved by not calling a tech for this to call them for
my other problem, which is a radiant baseboard unit that spews water way too
often. Now *that* I have no chance of fixing myself.

"RP" wrote in message
...


Max Metral wrote:

So, it turns out the therm IS a power stealing therm. What's strange is
that when EVERYTHING is off, I still have 0V across Y and R**, so of
course the therm has nowhere to steal power from when R and W are
connected. The obvious fix is to connect C (I don't have a labeled C on
the furnace board, will a screw terminal on the chassis do?) But the
most confusing part is that this has worked for years, and now suddenly
stopped. So I'm not sure if that means something has gone wrong with the
unit and I should tread carefully. I'm also not sure whether this is
just a little reminder that a 15 year old furnace should be scrapped.

Call a tech.

hvacrmedic


** In truth, it's not 0, it's some barely readable amount. The meter
moves, but hardly.

"RP" wrote in message
et...


Max Metral wrote:


Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So
I
swapped thermostats. It worked again for a couple of days, and then
failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will
come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but
it
SEEMS that the furnace is shutting off 24v when heat is called. It's
not
the blower though, because if I just turn the fan on (from the
thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat
line
directly, and the heat didn't come on, but I'm not sure if that's the
proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

If your thermostat takes batteries then replace them. A battery powered
t-stat with weak batteries will drop out when it attempts to bring in
heating or cooling, having enough power for the display, but not enough
for the internal relay circuits.

If your thermostat doesn't take batteries then it is a power stealing
stat, using Y to tap into common back through the compressor contactor.
Depending upon model Y may or may not go directly to the compressor
contactor--it may go instead through an electronic circuit on a main
control board. This type of system may require that a resistor be wired
across Y and C in the unit in order to provide a low resistance path from
Y to C. This type of stat usually comes with a large ceramic resistor
packaged with it.

There are also power stealing stats that also use batteries for backup.
The batteries in these are only provided to hold program and temp
settings in the event of a power failure.

Barring all of this it may be that your unit is shorted somewhere
internally which could cause power to drop at the transformer, and thus
from the t-stat when it calls for heat.

hvacrmedic

On Sun, 18 Dec 2005 07:46:52 -0500, "Max Metral"
wrote:

Hi. I have a Lenox furnace, about 15 years old I guess. It was working
fine, but then all of the sudden the thermostat seemed to just die. So I
swapped thermostats. It worked again for a couple of days, and then failed
again. So I debugged it a bit more carefully, and it turns out the
thermostat "resets" whenever it tries to call for heat. The fan will come
on for about a tenth of a second, and then the display acts like it does
when you first plug it in. I'm not sure exactly what's happening, but it
SEEMS that the furnace is shutting off 24v when heat is called. It's not
the blower though, because if I just turn the fan on (from the thermostat)
it works fine. It's also possible that the therm is somehow resetting
itself, the only real test I did here was connecting 24v to the heat line
directly, and the heat didn't come on, but I'm not sure if that's the proper
"protocol" for requesting heat.

Any thoughts before I call the techs?

Thanks,
--Max

You are on the right path. Just keep troubleshooting until you find
the culprit.
Look for a schematic on the furnace and you should find the controls
in the circuit, one of which is malfunctioning. Wiring and/or
connections could be the culprit too.

Max Metral wrote:

Well, the uncertainty about why this happened after two working heating
seasons will be a great unanswered question in my life. (ok, well, not that
great) BUT, the problem is solved.

So, as suspected, the digital therm was simply losing access to power when
it routed R to W. The additional variable that I didn't realize is that
there's a summer/winter hard switch on the furnace. I assumed that normally
I had switched this to winter in the past. However, with meter in hand if
the switch is on summer, I measure 24VAC across R and Y. If the switch is
on summer, I measure 0VAC. I don't understand exactly what this switch does
that other than I suppose forcibly disabling the compressor. But given this
fact, there's no way for the therm to steal power when it requests heat, and
it shuts off.
snip

So which is it when it's on summer -- 24VAC or 0VAC? (I think you
mis-typed in the above quote.) If this is an attic-mount furnace,
then my guess would be zero, which keeps the heat from coming on
when, e.g., an attic exhaust fan might be running (which could
lead to dangerous levels of CO).

It sounds to me like whoever installed the digital thermostat didn't
cover all the bases.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Yes, I mistyped, it should read:

....with meter in hand if the switch is on summer, I measure 24VAC across R
and Y. If the switch is on winter, I measure 0VAC across R and Y.

"CJT" wrote in message
...
Max Metral wrote:

Well, the uncertainty about why this happened after two working heating
seasons will be a great unanswered question in my life. (ok, well, not
that great) BUT, the problem is solved.

So, as suspected, the digital therm was simply losing access to power
when it routed R to W. The additional variable that I didn't realize is
that there's a summer/winter hard switch on the furnace. I assumed that
normally I had switched this to winter in the past. However, with meter
in hand if the switch is on summer, I measure 24VAC across R and Y. If
the switch is on summer, I measure 0VAC. I don't understand exactly what
this switch does that other than I suppose forcibly disabling the
compressor. But given this fact, there's no way for the therm to steal
power when it requests heat, and it shuts off.
snip

So which is it when it's on summer -- 24VAC or 0VAC? (I think you
mis-typed in the above quote.) If this is an attic-mount furnace,
then my guess would be zero, which keeps the heat from coming on
when, e.g., an attic exhaust fan might be running (which could
lead to dangerous levels of CO).

It sounds to me like whoever installed the digital thermostat didn't
cover all the bases.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Max Metral wrote:

Yes, I mistyped, it should read:

...with meter in hand if the switch is on summer, I measure 24VAC across R
and Y. If the switch is on winter, I measure 0VAC across R and Y.

Well, I think now I'm the one who mis-spoke. :-)

Having 24 VAC across R and Y in the summer is what you want, because
then you can effectively call for cooling. In winter, you'd want it
across R and W instead, to allow calling for heat. This could still
be part of an interlock with an attic fan.

"CJT" wrote in message
...

Max Metral wrote:


Well, the uncertainty about why this happened after two working heating
seasons will be a great unanswered question in my life. (ok, well, not
that great) BUT, the problem is solved.

So, as suspected, the digital therm was simply losing access to power
when it routed R to W. The additional variable that I didn't realize is
that there's a summer/winter hard switch on the furnace. I assumed that
normally I had switched this to winter in the past. However, with meter
in hand if the switch is on summer, I measure 24VAC across R and Y. If
the switch is on summer, I measure 0VAC. I don't understand exactly what
this switch does that other than I suppose forcibly disabling the
compressor. But given this fact, there's no way for the therm to steal
power when it requests heat, and it shuts off.

snip

So which is it when it's on summer -- 24VAC or 0VAC? (I think you
mis-typed in the above quote.) If this is an attic-mount furnace,
then my guess would be zero, which keeps the heat from coming on
when, e.g., an attic exhaust fan might be running (which could
lead to dangerous levels of CO).

It sounds to me like whoever installed the digital thermostat didn't
cover all the bases.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .





--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

On Monday 19 December 2005 12:43, Mark Lloyd wrote:

BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?

When I was young (not too long ago) I read in some sort of "home
emergencies" type of book something to the effect that you could screw
in a light bulb in the fuse box to locate or diagnose a short. The
bulb would glow brightly when there was too much current going through
it.

I'm guessing that if you screwed in a light bulb in a fuse box, the
brightness or dimness of the glow would depend on how much current was
being drawn on that circuit.

--
Travis Evans
[The email address on this post is valid, but may change from time to
time. Make sure you use the latest email address; if you use an old
one, I will not receive your message.]

"Travis Evans" wrote in message
news:BmHpf.437$Cw5.54@fed1read05...
On Monday 19 December 2005 12:43, Mark Lloyd wrote:

BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?

When I was young (not too long ago) I read in some sort of "home
emergencies" type of book something to the effect that you could screw
in a light bulb in the fuse box to locate or diagnose a short. The
bulb would glow brightly when there was too much current going through
it.

I'm guessing that if you screwed in a light bulb in a fuse box, the
brightness or dimness of the glow would depend on how much current was
being drawn on that circuit.


That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit
and it lights up to full brightness then you have a short circuit or some
device in the circuit that is drawing current. If you are sure there is
nothing in the circuit you look around and disconnect things tuil the light
goes out. If there could be a high current (more that an amp or two) device
in the circuit, you will have to disconnect it. Anything in the circuit
that uses less than a couple of amps will cause the light to burn dimmer.

Ralph Mowery wrote:
"Travis Evans" wrote in message
news:BmHpf.437$Cw5.54@fed1read05...

On Monday 19 December 2005 12:43, Mark Lloyd wrote:


BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?

When I was young (not too long ago) I read in some sort of "home
emergencies" type of book something to the effect that you could screw
in a light bulb in the fuse box to locate or diagnose a short. The
bulb would glow brightly when there was too much current going through
it.

I'm guessing that if you screwed in a light bulb in a fuse box, the
brightness or dimness of the glow would depend on how much current was
being drawn on that circuit.



That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit
and it lights up to full brightness then you have a short circuit or some
device in the circuit that is drawing current. If you are sure there is
nothing in the circuit you look around and disconnect things tuil the light
goes out. If there could be a high current (more that an amp or two) device
in the circuit, you will have to disconnect it. Anything in the circuit
that uses less than a couple of amps will cause the light to burn dimmer.

Sounds like a good way to burn down a house or to smoke a few small
appliances. For an encore you can slip a penny under the fuse. Dear
readers, please don't try any of this at home!

hvacrmedic

That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit

Of course, the sensible thing to do would be
to shut off the breaker, and test continuity from the nuetral to
the hot, but that requires a hunk of equipment that costs
several thousand pennies.

Goedjn wrote:

That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit


Of course, the sensible thing to do would be
to shut off the breaker, and test continuity from the nuetral to
the hot, but that requires a hunk of equipment that costs
several thousand pennies.

Before you do that, check the voltage between the two.

You're presumably working on a troubled circuit. Don't assume shutting
off the breaker eliminates all sources of electricity.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

On Mon, 19 Dec 2005 17:57:42 -0600, RP
wrote:



Ralph Mowery wrote:
"Travis Evans" wrote in message
news:BmHpf.437$Cw5.54@fed1read05...

On Monday 19 December 2005 12:43, Mark Lloyd wrote:


BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?

When I was young (not too long ago) I read in some sort of "home
emergencies" type of book something to the effect that you could screw
in a light bulb in the fuse box to locate or diagnose a short. The
bulb would glow brightly when there was too much current going through
it.

I'm guessing that if you screwed in a light bulb in a fuse box, the
brightness or dimness of the glow would depend on how much current was
being drawn on that circuit.



That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit
and it lights up to full brightness then you have a short circuit or some
device in the circuit that is drawing current. If you are sure there is
nothing in the circuit you look around and disconnect things tuil the light
goes out. If there could be a high current (more that an amp or two) device
in the circuit, you will have to disconnect it. Anything in the circuit
that uses less than a couple of amps will cause the light to burn dimmer.

Sounds like a good way to burn down a house or to smoke a few small
appliances. For an encore you can slip a penny under the fuse. Dear
readers, please don't try any of this at home!


Are you somehow equating a penny and a light bulb? A light bulb has a
much higher resistance, and (unless it got shorted somehow) could
never (on 120V) pass a current higher than 833mA (for a 100W bulb). It
wouldn't even conduct that much unless it was into a shorted circuit.

I used to work at Goodwill (for awhile), and they actually used light
bulbs in series for testing appliances.

hvacrmedic
--
5 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin

Mark Lloyd wrote:
On Mon, 19 Dec 2005 17:57:42 -0600, RP
wrote:



Ralph Mowery wrote:

"Travis Evans" wrote in message
news:BmHpf.437$Cw5.54@fed1read05...


On Monday 19 December 2005 12:43, Mark Lloyd wrote:



BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?

When I was young (not too long ago) I read in some sort of "home
emergencies" type of book something to the effect that you could screw
in a light bulb in the fuse box to locate or diagnose a short. The
bulb would glow brightly when there was too much current going through
it.

I'm guessing that if you screwed in a light bulb in a fuse box, the
brightness or dimness of the glow would depend on how much current was
being drawn on that circuit.



That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit
and it lights up to full brightness then you have a short circuit or some
device in the circuit that is drawing current. If you are sure there is
nothing in the circuit you look around and disconnect things tuil the light
goes out. If there could be a high current (more that an amp or two) device
in the circuit, you will have to disconnect it. Anything in the circuit
that uses less than a couple of amps will cause the light to burn dimmer.

Sounds like a good way to burn down a house or to smoke a few small
appliances. For an encore you can slip a penny under the fuse. Dear
readers, please don't try any of this at home!



Are you somehow equating a penny and a light bulb? A light bulb has a
much higher resistance, and (unless it got shorted somehow) could
never (on 120V) pass a current higher than 833mA (for a 100W bulb). It
wouldn't even conduct that much unless it was into a shorted circuit.

I used to work at Goodwill (for awhile), and they actually used light
bulbs in series for testing appliances.

Two reasons its a stupid idea:
Suppose the ohmic resistance of the light bulb is 240ohms (60watt
incandescent). Now suppose that the resistance at the short is 240ohms
when you have the bulb in place in the fuse box. Each load drops 60
volts for a total of 15watts dissipated at the short. Now suppose the
short is where a wire nut has fallen off. The wire junction has gotten
next to the fart fan housing and is arcing to the paper thin sheet
metal. There is a paper label inside the housing of the fart, opposite
the short, and the arcing sets this paper on fire. How long to you
think it will be before 15 watts continuously dissipating will get a
junction hot enough to ignite any combustible materials adjacent to it?
Arcing shorts can cause fires, and are in fact responsible for a large
number of electrical fires every year in the real world. The odds may be
against a fire starting in any one particular instance with this method
of short detection, but I'd hate like hell to be that one in
ten-thousand statistic on anything that I was diagnosing.

Now let's suppose that there is a small appliance plugged into an outlet
on that circuit. The voltage dropped across that appliance will vary
from 0 to 120 depending upon its resistance and upon the nature of any
upstream short which can vary from 0 to infinity ohms. Most appliance
won't be harmed with continuous low voltage for 5 to 30 minutes, but
some will. I also wouldn't want to be responsible for a smoked
electronic or motorized appliance.

A volt/ohmmeter can be obtained from any Walmart store for $10, (or
1,000 pennies even).

hvacrmedic