# Carrier furnace fan won't switch on



## Augment (Apr 7, 2010)

I have a 10 year old Carrier furnace.  When in heat/ac mode the fan will work, but it won't run continuously in "on" mode.  When the heat/ac is "off", and the fan is "on", it won't work at all.  It used to work continuously when in "on" mode.  The blower motor was replaced a few months ago and the problems started then. The LED light is not showing any problems. Is there a quick fix?


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## kok328 (Apr 7, 2010)

Check to see if the green wire or wire from the G terminal on the thermostat is hooked up and likewise at the thermostat terminal connections inside the furnace.


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## Augment (Apr 7, 2010)

yes, the green wire is hooked up on the thermostat and the furnace.


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## kok328 (Apr 7, 2010)

What happens when you jumper 24V from the red wired to the green wire?
If you remove the furnace panel door, make sure the safety switch doesn't cut power to the unit while testing.


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## Augment (Apr 7, 2010)

I wouldn't know how to do that - please explain!


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## kok328 (Apr 7, 2010)

Oh sorry, sometimes I assume too much.
Take a piece of wire and strip the two ends.
Touch one end to the "R" terminal and the other end to the "G" terminal on the thermostat terminal strip inside the furnace.
As I mentioned, there may be a safety switch that will kill power to the unit when the access panel is removed.  For the most part, you can just hold this in to restore power while testing.
Jumpering the R&G should run the blower motor.


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## Augment (Apr 7, 2010)

What would I be achieving by doing this?  I'm reluctant to try anything without knowing why I'm doing it.  The blower motor does work if it's in heat mode, just doesn't stay on continously even tho the fan setting on the thermostat is set to "on".


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## kok328 (Apr 7, 2010)

I'm trying to guide you in troubleshooting the circuitry of the unit.  This will basically tell us if the T-stat is bad or if there are other issues preventing the fan from working in the "On" setting.  It's only 24VAC so no safety issues to be concerned about.  If you prefer an alternate technique, you'll need a voltmeter.  Turn your tstat to fan "On" and check for 24VAC from ground to "G" (green).  This will tell me if the tstat is energizing the fan circuit or we can just energize it and see if the fan comes on which is what I was attempting in my prior post.


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## Augment (Apr 7, 2010)

I don't have a voltmeter, but will attempt the test tomorrow.  If the fan is energized this way, does it mean the tstat is bad?


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## kok328 (Apr 8, 2010)

If the fan turns on as a result of the test, it will either be a bad Tstat or the wiring from the Tstat to the furnace.
If you'd like, you can jumper the R & G terminals on the back of the Tstat and this will verify the wiring and result in determining a bad Tstat.


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## Wuzzat? (Apr 8, 2010)

Augment said:


> The blower motor was replaced a few months ago and the problems started then.


I think it's somewhat more likely that the problem is at the furnace end.


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## Augment (Apr 8, 2010)

I looked at the furnace,don't know where to start.  Jumping the t-stat seems easier.  What will this tell me if the fan does go on?


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## Augment (Apr 8, 2010)

I tried to jump on the tstat, nothing happened with green and red.  I accidentally touched red and yellow, started fan briefly then stopped (a/c mode).


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## kok328 (Apr 8, 2010)

What this tells us is that you could possibly have a bad wire from thermostat to furnace.
You'll have to jumper the R & G terminal at the furnace and see if the blower comes on.
Inside the furnace you'll see a wire coming in from the tstat.
Most likely brown insulation containing multiple colored wires.
What the thermostat does is completes a circuit of 24VAC from the R terminal to the G terminal to energize the fan circuit when fan "on".
If the G wire is bad, then power won't make it back to the furnace from the tstat.  So now we must energize the G terminal at the furnace to eliminate this possibility.  Inside the furnace you'll see the brown wire and it's multi-colored wires attach to the various terminals to run heat, A/C, fan, etc.
Touch the jumper wire to the R & G terminal and see if the fan comes on.


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## Augment (Apr 8, 2010)

I jumped the R & G terminals on the furnace and the fan did come on.  I should mention the G and Blue wires seem to share a terminal, don't know if this means anything.


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## kok328 (Apr 8, 2010)

On which terminal are the Green & Blue wires sharing (G or B)?


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## Augment (Apr 8, 2010)

G terminal


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## kok328 (Apr 8, 2010)

That's curious, based on what your telling me the fan should work when switched to "On".
We are going to have to back it up a step as I can't readily affect a repair online.
I need to know what wires (color) are attached to what terminals on both the furnace and thermostat.  Watch for crossed wires where the color and terminal does not match the opposite end (furance vs. tstat).
Just to be sure, this is not a heat pump system; correct?
We are definitely closing in on the problem but, I need more info to complete the picture.


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## Augment (Apr 8, 2010)

This is not a heat pump system, just forced air gas.  I've noticed that the wires hooked up to the thermostat and then reappearing at the furnace don't match.  On the thermostat there is an unattached blue wire, and attached white, yellow, green and red all attached to the correct terminals.

At the furnace, the thermostat wires are red attached to red, black attached to Y/Y2, white attached to W/W1, blue attached to green, orange attached to nothing.

I noticed that the green wire does not come from the tstat wires, it's in a separate bunch of wires of all colours.  However, it's connected to the G terminal and there's another connection to the fan (a plug that you can pull in and out to different fan levels).  Then the whole bunch leads back to the blower at the back of the furnace.

This is getting more and more complicated I think.  Thanks for your help!


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## kok328 (Apr 8, 2010)

Sorry, I forgot to ask whether there are any terminals where there are no wires attached on both the tstat and furnance ends.
Something is definitely mis-wired on purpose or on accident.
Not sure which is the case at this time.


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## Augment (Apr 8, 2010)

On the tstat, there's nothing on R2.  On the furnace, nothing on W2.


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## kok328 (Apr 8, 2010)

OK, one last question, is there a humidifier installed on this furnace?
I'm looking for a "C" terminal on the furnace and/or tstat.
Wifey is calling be back shortly (30mins) or so.


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## Augment (Apr 8, 2010)

Yes there is, and the thin black and white wires from these seem to go into this panel too.  the humidistat is on the furnace and is separate from the thermostat.

By the way, the green wire going to G on the furnace is labelled "rehum".


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## kok328 (Apr 8, 2010)

Any chance I can get a pic of the back of the tstat showing terminals and wires and likewise for the furnace compartment?

When did this problem start?

What has changed since it last worked?

This wiring doesn't make any sense and definitely does not follow conventions.
I just can't wrap my mind around this one.


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## Augment (Apr 8, 2010)

here are some photo's.  Thanks again.


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## Wuzzat? (Apr 8, 2010)

Post a legible schematic for the t'stat/furnace-input interface; this can be used for a 'brute force' way of figuring out what is going on.  This probably shows less than a half dozen wires, and it's the manuf. recommended configuration.  Your t'stat manual will show how it's internal switching is matched to its terminal designations.

The colors actually used for each function in your particular case can be sorted out afterwards.

A VOM will soon be necessary. . .


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## Augment (Apr 8, 2010)

As you can see from the photo's the schematic would be very complicated, not something I can tackle if I don't know what I'm supposed to label.  What is VOM??


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## Wuzzat? (Apr 8, 2010)

Augment said:


> the schematic would be very complicated
> What is VOM??


The complexity is what this forum handles, once we have the schematics, which you will find online or pasted on the inside of furnace panels.

It's a Volt-Ohm-Milliammeter.
http://static.howstuffworks.com/gif/home-repair-tools-ga-5.jpg


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## Augment (Apr 8, 2010)

here are some photo's of the schematic.  Hope they're legible.


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## kok328 (Apr 8, 2010)

I don't see where the yellow and green wires come into the furnace from the tstat.
It's almost like they splice the wire somewhere and the wire colors changed between the tstat and the furnace.
On the tstat I see white, yellow, green, red, and blue (with the blue not being used).
On the furnace I see white, black, red and blue.
A volt/ohm meter sure would be nice to have right now but, i think I know what's going on and can advise once you confirm what happened to the yellow & green wires.


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## Augment (Apr 8, 2010)

yeah, the yellow and green are a puzzle aren't they?  On the left of the photo you can see the thermostat wires, on the right are the green and yellow coming from somewhere else.  The green divides into two, one going into the G terminal with the blue wire and one going into the fan "board" (top middle).  Maybe the tstat wires were joined with another set of wires somewhere and the colors never matched up?  There is an a/c, humidifier and electronic air cleaner (not functioning for a few years) attached to this furnace.

The trouble started when the blower motor burned out after a violent summer storm.  We had the motor replaced, the fan wasn't at first working in the "on" position, but then it did start working again - this was when we used the a/c.  I think it stopped working a little while later when we switched from a/c to "off" between seasons.  The repair guy who replaced the motor wouldn't return calls to come see what's happening, no surprise.    I really need to find somebody competent to service this machine, but don't seem to luck out!

What does a VOM do?


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## kok328 (Apr 8, 2010)

I don't think that the yellow & green wires on the right side of the photo are tstat wires, they don't seem to be of the same guage wire.
As a final test, behind the tstat, strip back some insulation from the blue wire and touch it to the red terminal on the tstat.  I believe this will turn the blower on.  If so, attach the blue wire to the G terminal on the back of the tstat.  Not sure what to tell you to do with the green wire on the back of the tstat, so try it (meaning turn your stat to fan switch to "ON" after attaching the blue wire) with and without the green wire attached to the G terminal on the back of the tstat.  Depending, the G terminal on the tstat will have either both the green and blue wire attached or just the blue wire if the test is sucessful.
Man what a mess, sorry this is taking me so long to troubleshoot.

P.S.-
A VOM (volt/ohm meter) or DMM (digital multi-meter) measures voltage, ohms and continuity (and other functions depending on the make and model).  They come in handy for telling us what is being energized when the unit is set to certain settings and can tell us if there are shorts in the wiring.

I'll check up on ya in the morning but, please do post back whether we have fixed the problem, it's always nice to know the outcome.


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## Augment (Apr 8, 2010)

I'll test it in the morning.  Is it ok to hook up the green and blue together on one terminal if need be? Thanks.


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## Augment (Apr 9, 2010)

Good morning.  Nothing happened when I touched the blue to the red, no blower, no response from the furnace.


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## kok328 (Apr 9, 2010)

Your going to have to trace the wires from the tstat to the furnace and see if it is a continuous run.  I'm not convinced that it is.  If it is, I need to clearly see where the yellow and green wire go and where the black wire in the furnace is coming from.


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## Wuzzat? (Apr 9, 2010)

Thanks for the schematic.  
I wonder if the HVAC guy changed the dipswitch settings and this is the cause of your problems.

http://mti09spring.files.wordpress.com/2009/02/dip_switch_01_pengo2.jpg

You have a link to your 'stat?


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## kok328 (Apr 9, 2010)

No, the dipswitch settings control the speed and on/off delay.
He was able to get the fan to run by jumpering the R & G terminals in the furnace.  I'm convinced that the same can be accomplished at the tstat but, the wires that leave the stat aren't the same as those inside the furnace.
He'll have to figure out where the splice is and which wires got crossed to get this to work.  The blue wire on the G terminal in the furnace is suppose to lead back to the green wire on the G terminal on the stat but, this didn't pan out.


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## Wuzzat? (Apr 9, 2010)

kok328 said:


> No, the dipswitch settings control the speed and on/off delay.
> He was able to get the fan to run by jumpering the R & G terminals in the furnace.  I'm convinced that the same can be accomplished at the tstat but, the wires that leave the stat aren't the same as those inside the furnace.
> He'll have to figure out where the splice is and which wires got crossed to get this to work.  The blue wire on the G terminal in the furnace is suppose to lead back to the green wire on the G terminal on the stat but, this didn't pan out.



I guess one way to handle this messy problem is to dismount the 'stat and run 5 short wires from the proper terminals on the 'stat to the proper terminals on the furnace connector.  

If that works properly [I'd be monitoring the 24v 'former output during this test to make sure we're not dealing with a short circuit] 
the OP can run a new 5 conductor cable in the wall and have the wire colors conform to the conventional color code, if there is an accepted color code.  This color convention seems to be up for discussion.
Thermostat Wiring Colors - Thermostats Wire - Installation Basics-HVAC

But the current config. needs to be thoroughly documented so that the OP can return to it if necessary.  The worst outcome is that fewer functions work than before.

Alternately, with the existing 24v 'former and a load [two 1w or 2w, 12v incand. lamps from Radio Shack in series] the 'stat can be checked for proper switching depending on the function selected, but the 'stat pinout is necessary for this.


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## Augment (Apr 9, 2010)

ok guys, I've found where they spliced the tstat wires and changed the coloring.

From Tstat:

Yellow = Black at furnace
Green = Blue at furnace
White = White at furnace
Red = Red at furnace

I have no idea what your previous postings were about, I really have no experience with this, so technical jargon goes right over my head! What is a "stat"?  Thanks.


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## Wuzzat? (Apr 9, 2010)

Augment said:


> What is a "stat"?


Thermostat = t'stat = 'stat.
Transformer = t'former = 'former = 'frmr

The " ' " stands for missing characters and sometimes, as in "gotta'" for "got to", stands for intentional slang usage.
Don't = do not.
Wit'cha = with you

For extra credit, what does "muvva'" mean? 

I think Mr. 328 will have this fixed soon!


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## Augment (Apr 9, 2010)

got it, tks.


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## kok328 (Apr 9, 2010)

I'm glad you found the splice, I was starting to question myself. 
Ok, based on what I'm reading you should be able to turn the fan switch to "on" on the tstat (thermostat) and the fan will run.  It maybe that you have to have your furnace in a mode (heat or A/C) for the fan to work.  You don't necessarily have to have it set so it cools or heat but, just in that mode/setting.

If not, we are back to 
- bad tstat
- a break in the green wire from tstat to splice
- or a break in the blue wire from splice to furnace

Without a multi-meter, we will have to start swaping wires to eliminate the problem.
Let me know.


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## Augment (Apr 9, 2010)

well, the good news is the fan works in "on" position with no  heat.  I tightened the nut on the furnace where blue goes in and it worked.  HOWEVER, the heat now doesn't go on!!  I've tried waiting a while before switching to heat, tried turning power off to furnace and on again, but no heat.  What color wires are for heat?  Maybe I need to adjust those too????  Maybe they got unhooked while I was fiddling with all that electrical tape surrounding the splice.  Yikes, I'm going crazy.


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## kok328 (Apr 9, 2010)

Your going crazy?  I'm was losing my mind over this until you confirmed the splice.  LOL.

I was just about to edit my previous post and tell you to check the connections at the splice as the blue/green connection is in question.

Here's the breakdown on wire color/function.
Red = 24VAC
White =Heat
Green = Fan
Yellow = A/C
I'll let you do the interpretation for your particular situation.  Good Luck.
Check all terminals both furnace and tstat and recheck the splice connections.
This wire is thin guage solid core and breaks easily when twisted in a splice.
If you want to invoke the heat as we did the fan, touch your jumper wire between the W & R terminals in the furnace and the heat will come on.


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## Augment (Apr 9, 2010)

ok, amazing news, fan works, heat's back on!  I respliced the two white wires with a wire nut (it was previously coated with a gooey substance), redid the electrical tape and voila it worked.  I hope the wiring can keep it together as the weather's gotten cooler here again.

Thanks for all your help you guys!  You probably saved me a $500 repair bill.  I've also learned some valuable info about the workings of this monstrous machine and tstat.  Thanks again, have a great weekend.


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## Wuzzat? (Apr 9, 2010)

Augment said:


> ok, amazing news, fan works, heat's back on!


"snatch victory from the jaws of defeat
. . .to win at the last moment."


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## kok328 (Apr 9, 2010)

Glad to hear your up and running.  Sorry it took me so long to troubleshoot the problem.


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