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Author Topic: HVAC help... furnace blower not kicking on  (Read 7733 times)

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Offline cyberwollf

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HVAC help... furnace blower not kicking on
« on: October 01, 2011, 08:21:03 »
Anybody do HVAC work/help?  Its a 80's Lennox gas furnace.  On a call for heat: the pilot kicks on, ignites, LED on the ignition control is on so induction motor is pulling good vacuum, main burners kick on, but the main blower never kicks on.

I've done a fair amount of googling, I think its the fan limit switch.  I can watch it take little jumps and it gets over 100, but after about 2 mins after the main burners started the limit switch jumps to 150 and everything shuts down... How smooth should the limit switch dial climb, and when should the main blower turn on?

Right now i just set it for heat and after it lights i turn the blower on manually to blow the hot air.

Ideas?
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline kattz

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Re: HVAC help... furnace blower not kicking on
« Reply #1 on: October 01, 2011, 09:26:58 »
If you have a modern furnace, there are fuses on the main board.  Check those.  Most furnaces have a purge blower that is usually a small motor and fan attached to the burner box that comes on first.  This trips a pressure switch once on that turns on the main fan and burners.  Both my fan motor and switch have went bad and I've replaced them separately over the past 13 years.  If you turn the plastic indicator wheel on the back of the purge fan motor and then it takes off, the bushings are going bad but the motor will run for a few weeks. Also, there's a hi-limit thyristor or snap switch on the furnace.  If this goes bad, the furnace will not start.

Most furnaces built in the past 15 years have an LED indicator that will blink a trouble code to tell you what's missing or what's wrong.  You will need one or two jumper wires to bypass the sensors and a meter to troubleshoot.

HTH.

Kev
90g SPS and LPS reef tank, 35g sump, ceramic rock by The Alternative Reef, Neptune Apex w 2 X EB8's, Moonlight module, ATI Sunpower Dimmable 8 X 39W T5's, Octopus Extreme 160 skimmer, PM Kalkwasser Reactor, 2 X Vortech MP40's, Geo 618 Ca reactor


Various thriving montipora, acropora, stylopora, wellsophyllia, blastomussa, hammer, anchor, and frogspawn, lobophyllia, rhizotrychus, pavona, scroll, and pagoda SPS and LPS corals, but no fish because I was too stupid to QT...

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #2 on: October 01, 2011, 16:45:37 »
If you have a modern furnace, there are fuses on the main board.  Check those.  Most furnaces have a purge blower that is usually a small motor and fan attached to the burner box that comes on first.  This trips a pressure switch once on that turns on the main fan and burners.  Both my fan motor and switch have went bad and I've replaced them separately over the past 13 years.  If you turn the plastic indicator wheel on the back of the purge fan motor and then it takes off, the bushings are going bad but the motor will run for a few weeks. Also, there's a hi-limit thyristor or snap switch on the furnace.  If this goes bad, the furnace will not start.

Most furnaces built in the past 15 years have an LED indicator that will blink a trouble code to tell you what's missing or what's wrong.  You will need one or two jumper wires to bypass the sensors and a meter to troubleshoot.

HTH.

Kev

The little motor is the unduction motor, and my LED is solid so i am getting a good signal from the pressure switch.  Normally there is a ~1 min delay between burners lighting and main blower start.  There is another temp limit switch that is controlled by burner heat to ensure it doesnt blow cold air and keeps blowing warm air even after the burners kick off.  I think this switch is bad, but have no idea how to troubleshoot it
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline reefit

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Re: HVAC help... furnace blower not kicking on
« Reply #3 on: October 01, 2011, 17:16:48 »
does the blower turn on if you move the fan limit buy hand? if it does fan limit is bad if it doesn't blower is bad.

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #4 on: October 01, 2011, 19:23:50 »
does the blower turn on if you move the fan limit buy hand? if it does fan limit is bad if it doesn't blower is bad.

Nope.  fan limit is pretty firm.  I can spin it like 20 degrees maybe, then it snaps back to its correct temp.

blower should be on between 100-150 right? after 150 it is saftey cutoff?  I dont here any relay clicks or anything when i move it inside or out of the 100-150 zone.. should i?
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline kattz

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Re: HVAC help... furnace blower not kicking on
« Reply #5 on: October 01, 2011, 20:02:25 »
No, you won't hear anything.  Pull the wires off of the sensor in question.  If the furnace works, it's a bad sensor. If that doesn't work, use a piece of wire and jumper the two terminals.  If it still doesn't work, look for the problem elsewhere.
90g SPS and LPS reef tank, 35g sump, ceramic rock by The Alternative Reef, Neptune Apex w 2 X EB8's, Moonlight module, ATI Sunpower Dimmable 8 X 39W T5's, Octopus Extreme 160 skimmer, PM Kalkwasser Reactor, 2 X Vortech MP40's, Geo 618 Ca reactor


Various thriving montipora, acropora, stylopora, wellsophyllia, blastomussa, hammer, anchor, and frogspawn, lobophyllia, rhizotrychus, pavona, scroll, and pagoda SPS and LPS corals, but no fish because I was too stupid to QT...

Offline ohioreef

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Re: HVAC help... furnace blower not kicking on
« Reply #6 on: October 01, 2011, 20:21:25 »
Our furnace doesn't use the fan limit switch to control the blower, it is controlled by the control board. It kicks it on a certain time after main burner fires. The fan limit switch is used to shut down the burner if the furnace overheats.

If it is blowing on manual then you can rule out the blower itself.

When I was having problems with our furnace last year I got a lot of help from the forums at http://www.doityourself.com/forum/.

Offline ohioreef

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Re: HVAC help... furnace blower not kicking on
« Reply #7 on: October 01, 2011, 20:22:54 »
Pull the wires off of the sensor in question.  If the furnace works, it's a bad sensor. If that doesn't work, use a piece of wire and jumper the two terminals.  If it still doesn't work, look for the problem elsewhere.

Not necessarily. On my furnace some of the sensors complete the circuit to allow the furnace to run. Pulling a wire shuts down the furnace.

Offline reefit

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Re: HVAC help... furnace blower not kicking on
« Reply #8 on: October 01, 2011, 21:16:12 »
Does the blower come on when you turn the thermostat from auto to on? If it comes on it will be the fan limit if it doesn't come on it's most likely the blower motor.

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #9 on: October 01, 2011, 21:17:30 »
Our furnace doesn't use the fan limit switch to control the blower, it is controlled by the control board. It kicks it on a certain time after main burner fires. The fan limit switch is used to shut down the burner if the furnace overheats.

If it is blowing on manual then you can rule out the blower itself.

When I was having problems with our furnace last year I got a lot of help from the forums at http://www.doityourself.com/forum/.

Thanks for the info Gary.  How were where you able to tell whether it uses the limit switch for blower or just overtemp?

That sounds like what i got, playing with the limit switch i can never get the blower to kick on, but if i let it run 2 mins or so without the blower on, it will jump to the 150 cutoff and it will kill the control board.

The only thing that doesnt add up is, the controll board LED is always solid, it doesnt blink any error messages AND the control board was replaced winter 2008....
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #10 on: October 01, 2011, 21:19:22 »
Does the blower come on when you turn the thermostat from auto to on? If it comes on it will be the fan limit if it doesn't come on it's most likely the blower motor.

Yes it comes on in manual, thats how i have it running now.  how do i determine/troubleshoot whether the control board or limit switch activate the blower?

There is only 1 relay on the blower right?  The thermostat, AC, and furnace all activate the same relay for blower?
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline reefit

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Re: HVAC help... furnace blower not kicking on
« Reply #11 on: October 01, 2011, 22:11:54 »
with out seeing it i would call it bad fan limit how many wires are on the fan limit?

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #12 on: October 01, 2011, 22:15:52 »
with out seeing it i would call it bad fan limit how many wires are on the fan limit?

Do you do HVAC work? If so are you intrested in comming to check it out for a 6pack or reef related trade ;)
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline reefit

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Re: HVAC help... furnace blower not kicking on
« Reply #13 on: October 01, 2011, 22:32:03 »
i do apartment maintenance. i don't have the part you need

Offline ohioreef

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Re: HVAC help... furnace blower not kicking on
« Reply #14 on: October 02, 2011, 14:54:03 »
Can you post a picture of the limit switch? Does the blower wires connect to the switch or to the control board?

Do you have an owner's manual? That should cover how the blower is turned on.

When you say you turn the blower on manually, are you flipping a switch on the limit switch or using the thermostat fan switch?

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #15 on: October 02, 2011, 15:51:14 »
Can you post a picture of the limit switch? Does the blower wires connect to the switch or to the control board?

Do you have an owner's manual? That should cover how the blower is turned on.

When you say you turn the blower on manually, are you flipping a switch on the limit switch or using the thermostat fan switch?

Ill get a pic when i get back home.  i am flipping the themostat fan from "auto" to "on" before the limit switch maxs out at 150 and kills the control board from overheat.  it operates fine like this

ill get back with pics.  from what i remeber, 2 wires from control board to switch, 2 wires from switch to gas solinoid, and 2 wires from switch to blower
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline kattz

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Re: HVAC help... furnace blower not kicking on
« Reply #16 on: October 02, 2011, 19:39:25 »
You know, there's this new invention called a "repairman"...
90g SPS and LPS reef tank, 35g sump, ceramic rock by The Alternative Reef, Neptune Apex w 2 X EB8's, Moonlight module, ATI Sunpower Dimmable 8 X 39W T5's, Octopus Extreme 160 skimmer, PM Kalkwasser Reactor, 2 X Vortech MP40's, Geo 618 Ca reactor


Various thriving montipora, acropora, stylopora, wellsophyllia, blastomussa, hammer, anchor, and frogspawn, lobophyllia, rhizotrychus, pavona, scroll, and pagoda SPS and LPS corals, but no fish because I was too stupid to QT...

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #17 on: October 02, 2011, 19:49:29 »
You know, there's this new invention called a "repairman"...

You paying the bill? lol

Nothing is "broken" so why pay someone to fix it.  just gotta figure out why it doesnt kick on automaticlly
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline Wall_Tank

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Re: HVAC help... furnace blower not kicking on
« Reply #18 on: October 02, 2011, 19:59:23 »
You paying the bill? lol

Nothing is "broken" so why pay someone to fix it.  just gotta figure out why it doesnt kick on automaticlly

I love your definition of "Nothing is "broken""

It is supposed to come on automatically, but doesn't.   Seems like it's working to me.

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #19 on: October 02, 2011, 20:12:38 »
come on! as DIY as we all are dont give me crap about this!  Kattz im sure never work on your cars when they break, you just bring them into the dealership and get gouged.
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline ohioreef

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Re: HVAC help... furnace blower not kicking on
« Reply #20 on: October 02, 2011, 20:32:07 »
Personally, I don't call a repairman until I absolutely have to! With as much information as there is on the internet I can usually troubleshoot it myself and fix it. That being said, I do know the limits of my abilities.

Offline Wall_Tank

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Re: HVAC help... furnace blower not kicking on
« Reply #21 on: October 02, 2011, 20:56:11 »
come on! as DIY as we all are dont give me crap about this!  Kattz im sure never work on your cars when they break, you just bring them into the dealership and get gouged.

Just giving you a hard time.........

Offline kattz

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Re: HVAC help... furnace blower not kicking on
« Reply #22 on: October 02, 2011, 20:57:08 »
come on! as DIY as we all are dont give me crap about this!  Kattz im sure never work on your cars when they break, you just bring them into the dealership and get gouged.

Wes, other than paying someone for refrigerant, I've NEVER had to pay someone to repair my furnace or AC.  My cars get worked on because a) they are under warranty, and b) I don't have time to change my own oil.  I fix my own appliances, even board-level repairs on my TV's.  But I'm with Ohioreef on this one; I know when to call it quits.  Did you jump out the sensors like I recommended?
90g SPS and LPS reef tank, 35g sump, ceramic rock by The Alternative Reef, Neptune Apex w 2 X EB8's, Moonlight module, ATI Sunpower Dimmable 8 X 39W T5's, Octopus Extreme 160 skimmer, PM Kalkwasser Reactor, 2 X Vortech MP40's, Geo 618 Ca reactor


Various thriving montipora, acropora, stylopora, wellsophyllia, blastomussa, hammer, anchor, and frogspawn, lobophyllia, rhizotrychus, pavona, scroll, and pagoda SPS and LPS corals, but no fish because I was too stupid to QT...

Offline cyberwollf

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Re: HVAC help... furnace blower not kicking on
« Reply #23 on: October 03, 2011, 09:56:47 »
Wes, other than paying someone for refrigerant, I've NEVER had to pay someone to repair my furnace or AC.  My cars get worked on because a) they are under warranty, and b) I don't have time to change my own oil.  I fix my own appliances, even board-level repairs on my TV's.  But I'm with Ohioreef on this one; I know when to call it quits.  Did you jump out the sensors like I recommended?

I was just punching back at you :) With being a aircraft maintainer, im sure you do alot a of mechancical work yourself.  I think i am going to break down on this one, just havent had time to troubleshoot it properly.  Soon as I realized it wasnt the burners or blower (big ticket items) I wasnt too worried.  The controller board is only $200 so it has broken again (<2 years) i just HATE paying peoples labor rate.  I'd actually rather pay someone for 30 mins worth of time to tell me what is wrong and I go fix it, rather than paying them to replace I board that i could just as easily have done... Im Just cheap. :)  I should have time today to spend a few hours looking at the schematic to find the problem.  Im really thinking its a thermocouple or relay or something cheap, just gotta narrow it down to that.
75G Mixed Reef w/ 30G sump/refuge

Electrical Engineers do it on impulse, with faster rise times, with more power, and less resistance at higher frequencies, without shorts, until it Hertz


Offline ohioreef

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Re: HVAC help... furnace blower not kicking on
« Reply #24 on: October 03, 2011, 13:06:52 »
If the burner is remaining burning it's not a thermocouple. If the blower runs when switched to manual I doubt it's a relay.

Depending on what triggers the blower to turn on, I'd suspect the limit switch or controller.

 

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