change blower speed on G43UF furnace


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Old 03-06-08, 04:50 AM
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change blower speed on G43UF furnace

Can anyone advise how to change the blower speed on a Lennox G43UF furnace? It says nothing to this extent in the manual (of course) and I can't find anything on the net.

Thank you to anyone that can help.
 
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Old 03-06-08, 05:39 AM
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What speed you need to change, heating or cooling? Why the need for change in speed?

If for heating, what is the temp rise across the heat exchanger?
 
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Old 03-06-08, 10:36 AM
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I would like to change it to the next lower speed for both heating and a/c.

It sounds like a plane taking off for starters (quiet unit my foot). It's a G43UF 48C 090 (110,000 btu)

It's also cylcling on and off too often which doesn't take much moisture out of the air in the summer and hardly any humidity is added in the winter.

Apparently the motor has a few speeds and I wanted to see if this would help in both cases.
 
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Old 03-06-08, 11:33 AM
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How big is your home?

What's the model on the A/C?

I need you to take a temp reading at the return near the air filter, and near the coil, let the furnace run 10 min or so, I want to see what your temp rise to see if it's safe to drop the blower down.
 
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Old 03-06-08, 06:07 PM
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The house is 2725 sq/ft and the a/c is a 3 ton 13 seer Armstrong I believe it's the 213le model.

"Near the coil" I assume you mean the a/c "A" coil?

I can get a reading by removing the humdifier flange attached to the plenum which is just above the top of the "A" coil.

Will a regular thermometer do?
 
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Old 03-06-08, 06:59 PM
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yeah, any type will work out, as long you can read in the 1--˚ range when you take a reading near the A/C coil.

Like I said, the furnace needs to be running about 10 min to get a good reading.
 
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Old 03-07-08, 05:00 AM
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I will try to do that over the weekend.

There's a nasty winter storm heading this way and I have to buy a thermometer that will do that.
Hopefully I can get you the info early next week.

Thanks for all your help Jay.
 
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Old 03-10-08, 05:58 AM
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Jay...I was just thinking, should I get the temperature with the humidifier hooked up or should I unhook it from the plenum?
I just thought that with the humidifier bringing in some of the hot air from the plenum it might skew the temperature reading at the return near the air filter. Please advise if it matters.

Thank you.
 
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Old 03-10-08, 06:07 AM
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Leave it hooked up, that way we can take that into an account of the temp rise.
 
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Old 03-10-08, 01:17 PM
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If you slow your blower down, your heating cycle will be even shorter.

DL
 
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Old 03-10-08, 02:10 PM
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Wink

Have you checked on the blower door there. Should be a wire schematic that will show the speeds and where they go.

It's also cylcling on and off too often which doesn't take much moisture out of the air in the summer
. It should not go on and off when the AC is running. if you slow the blower down it will take more humidity out of the home on the AC. If you put the tstat to fan on will it run all the time?????
 
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Old 03-12-08, 07:01 PM
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Jay,

I let the furnace run for 10 minutes but it took about another 10 minutes to get a reading from the "A" coil because I used a digital thermometer and it took that long before it stopped climbing and then another 5 minutes or so to get the cold air temperature.
Over the "A" coil it was 45.5 deg Celsius (114 deg. Fahrenheit) and the return was 22.2 deg. Celsius (72 deg. Fahrenheit).

Ed,
I don't usually leave the fan on since it sucks energy (not a variable speed) and sounds loud but I assume the A/C will only come on when the tstat calls for it.

Delta,
If the blower is slower it will take longer to heat the house and the air should be hotter so it should work longer and the house should take longer to cool so how would the cycle be even shorter?
 
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Old 03-12-08, 08:57 PM
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Ok, You got a 42˚f temp rise, and your furnace spec says temp rise of 40 to 70˚f rise, and looks like we can drop another notch.. Take a reading again and see what the rise is.
 
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Old 03-14-08, 07:46 PM
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Hi Jay,

I took another reading and it was 22.6 deg Celsius (72.7 Fahrenheit) Celsius at the return and 46.5 deg Celsius (115.7 deg Fahrenheit) in the plenum near the coil.
 
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Old 03-14-08, 07:52 PM
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43˚f You're good to drop the speed down, when you are done making the change, take a reading, just don't get close to 70˚f rise.
 
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Old 03-15-08, 12:39 PM
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How exactly do I do that and how do I know what speed I am in?
 
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Old 03-15-08, 02:58 PM
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MAKE SURE POWER IS OFF!!

Ok, On the top half, you'll see a print on the board saying "HEAT-H" and "COOL-H". then "PARK" is the "dead' wire that won't be used.

What color is placed on Heat and Cool? I'm guessing you have Yellow on Heat, and Black on Cool.

I would change Red to heat, and Brown to Cool. If you find the humidity is still kinda high, then can drop it down to Yellow on Cool.
 
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Old 03-16-08, 03:26 PM
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Right now the black is on cool and brown is on heat.
Yellow and red are on park.
So what speed is it in now?
With what you are suggesting what speed would it then be in?
How do you figure out the speeds anyway?
The label on the furnace cover is vague.
 
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Old 03-16-08, 04:28 PM
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Originally Posted by diywanabee
Right now the black is on cool and brown is on heat.
Yellow and red are on park.
So what speed is it in now?
With what you are suggesting what speed would it then be in?
How do you figure out the speeds anyway?
The label on the furnace cover is vague.
Black is High
Brown is Med-Hi
Yellow is Med-Lo
Red is Low

Since your brown is on Heat, change it down to Yellow, and take a temp rise reading.
 
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Old 03-23-08, 10:06 AM
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Thanks Jay for all your help.
I get it now and will be careful if I change to the red wire.

Unfortunately the humidity is still not rising and unaffected by slower speed and I don't know if changing to the red would have any effect at this point.I have a GeneralAire 900 Elite 17/gal a day and it just seems to puts the water down the drain. I can't get the humidity over 34°.

Have you any suggestions? Or should I post this on the humidifier section? Please advise.
 
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Old 03-23-08, 05:38 PM
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You did drop the blower speed down?

What are your temps out now? Avg run time since you made the changes?
 
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Old 04-23-08, 10:03 AM
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Hi Jay,

Sorry for not replying sooner but been running around lately and haven't had time to deal with this.
Now the weather is so warm that I don't want to run the furnace at this stage.
If it doesn't cool down sufficiently soon I may have to wait until next heating season to take this up again.
I'll touch base with you again when I do.

Thanks a lot for your help.
 
 

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