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furnace blows cold air



 
 
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  #1  
Old January 24th 06, 10:57 PM posted to alt.home.repair
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Default furnace blows cold air


Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ

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  #2  
Old January 24th 06, 11:20 PM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air


wrote in message
oups.com...

Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ



Your reasoning makes sense, but I doubt that it's that simple. I have a
similar furnace (different brand). The start-up sequence is the same.
However, when I asked about DIY service should something go wrong, the
installer said that I should read the book first and then look at the "error
codes" that flash when the furnace doesn't operate. He pointed out a little
bank of LEDs that blink the error codes. That tells me there's a computer
in there someplace and just about anything could be going on.

Before getting into the hardware, my suggestion is to read the
installation/service manual to see if you can get any clues from the furnace
itself. If you don't have the book, check on the web. Many can now be
downloaded. I always check for the obvious -- tripped circuit breaker,
loose wires, etc., and then try shutting off the power for a minute or so.
That resets the computer.

TKM


  #4  
Old January 25th 06, 01:24 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air

wrote:
Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ

Hi,
Read the manual?
Error code? If I must guess, flame sensor is not sensing the flame if
you visually confirmed flame ignited.
Good luck,
Tony
  #5  
Old January 25th 06, 01:28 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air


I would think you are on track. First, verify the gas is making it to
the furnace. Make sure you hear the 'click' that opens the gas valve
for the ignitors to fire. It's an electrical activated solonoid that
you can hear or check with an ohm meter. Next, find that thermal
protection fuse which should be located near the burners. Look on a
site that sells them so you'll know what you're looking for. They have
two leads and should read zero ohms if it's good. I would certainally
hire a professional if the problem is beyond this.

J



wrote:
Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ

  #6  
Old January 25th 06, 01:37 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air

I believe he said "the burners never fire up".

"Tony Hwang" wrote in message
news:SqABf.324696$2k.208307@pd7tw1no...
wrote:
Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ

Hi,
Read the manual?
Error code? If I must guess, flame sensor is not sensing the flame if
you visually confirmed flame ignited.
Good luck,
Tony



  #7  
Old January 25th 06, 01:39 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air

My money is on a sticking relay, but I agree that he should hire a
professional.

"Joey" wrote in message
...

I would think you are on track. First, verify the gas is making it to
the furnace. Make sure you hear the 'click' that opens the gas valve
for the ignitors to fire. It's an electrical activated solonoid that
you can hear or check with an ohm meter. Next, find that thermal
protection fuse which should be located near the burners. Look on a
site that sells them so you'll know what you're looking for. They have
two leads and should read zero ohms if it's good. I would certainally
hire a professional if the problem is beyond this.

J



wrote:
Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ



  #8  
Old January 25th 06, 02:00 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air

Bob, that is a possibility, but I'm sitting here looking at a bag of 50
thermal fuses that I purchased just for this problem. My last job was a
Trane unit with a bad thermal fuse. I cleaned around the burner
entrance and replaced the fuse and problem solved.

J


Bob wrote:

My money is on a sticking relay, but I agree that he should hire a
professional.

"Joey" wrote in message
...

I would think you are on track. First, verify the gas is making it to
the furnace. Make sure you hear the 'click' that opens the gas valve
for the ignitors to fire. It's an electrical activated solonoid that
you can hear or check with an ohm meter. Next, find that thermal
protection fuse which should be located near the burners. Look on a
site that sells them so you'll know what you're looking for. They have
two leads and should read zero ohms if it's good. I would certainally
hire a professional if the problem is beyond this.

J



wrote:

Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ




  #9  
Old January 25th 06, 02:43 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air


I apologize profusely. In my haste, I gave wrong info in the previous
post.

I just spent the last hour with the panel off the furnace, looking for
obvious problems (burnt wires etc) and re-checking what's happening.

The blower motor is NOT coming on. The vent (exhaust) motor IS coming
on.

When I dial up the thermostat to request heat, all that happens is that
the vent motor turns on. It stays that way for as long as I leave the
thermostat turned up. The igniter never glows, the gas does not turn
on (no gas smell), and there is no fire.

When I dial the thermostat back down, the vent motor shuts off after
about 30 seconds.

This unit has a White-Rodgers model 50A50-206 control with the
diagnostic LED. The LED does not indicate any problem (no flashes).

Just to confirm that the control was not dead, I removed one wire from
the vacuum sensor that monitors the vent motor's suction. Then I got 3
flashes on the control's diagnostic LED, indicating that the sensor was
stuck open. So the control was healthy enough to detect that.

What are the most likely culprits here? Does a failed igniter fit
these symptoms? Is the igniter easy to test? How? I'm assuming that
the White-Rodgers control does not monitor the igniter, because there
is no error code listed for it. The error codes from the
White-Rodgers are pretty limited. It's not like a modern auto computer
which monitors just about everything.

I'm not smelling any gas *at all*, so the control is apparently not
opening the valve. Is it supposed to, even if the igniter is faulty?
In other words, does the control monitor the health of the igniter,
and refuse to open the gas valve if it's not glowing? Or does it just
wait a short time, then open the gas valve, and if the temperature
doesn't rise rapidly it turns the gas back off?

  #10  
Old January 25th 06, 10:59 AM posted to alt.home.repair
external usenet poster
 
Posts: n/a
Default furnace blows cold air

On 24 Jan 2006 14:57:13 -0800, wrote:


Hello.

I have an Amana Air Command Hi Efficiency 90 Gas Furnace that just
stopped working this afternoon. I noticed that cold air was blowing
out the heat registers and the temperature in the house was 8 degrees
below the thermostat setting.


This furnace is a pilotless unit with a hair-dryer-shaped exhaust fan
to vent the exhaust gases.


Here is how the furnace normally operates (to the best of my memory):

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting, requesting heat

- there is a short delay (for the igniter to heat up?)

- the gas kicks in and ignites and the exhaust fan turns on

- there is another short delay (for the heat exchanger to come up to
temperature?)

- the blower fan kicks in and voila, there's heat




Here is the present abnormal operation:

- the thermostat "cool-off-heat" switch is on "heat"

- the thermostat fan "on-auto" switch is on "auto"

- I turn up the thermostat setting

- the blower fan *immediately* comes on and starts blowing unheated air
throughout the house

- the exhaust fan never comes on

- there is no gas smell, and the burners never fire up

- I cannot see any indication of an igniter heating up (not sure where
to look, but I think if there was something glowing in there I would
see it)


Here is my working hypothesis: There is a thermal safety sensor/switch
somewhere in there that thinks the heat exchanger is overheated. So
even though the heat exchanger is dead cold, it wants to keep the
blower motor on to cool it off. And it inhibits the ignition and the
release of gas to the burners. So when I turn the thermostat up,
requesting heat, all I get is the blower motor coming on.

Does my reasoning make sense?

And, is it pretty straightforward to replace the thermal safety switch?

And, where is said switch/sensor?

And finally, is there a quick and simple way to momentarily bypass the
thermal safety switch to test my hypothesis... so I don't waste time
and money buying the wrong part?

Thanks.

EJ


There is no way to troubleshoot a system over the internet. it would
be best to call a local company to check it on site.
++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++
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