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Old 06-13-2010, 08:35 PM   #1
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Why do you have to screw in a different wire to change the fan speed?


When my HVAC unit was serviced a couple years ago the technician said that the fan could be set on three different speeds (for cooling) and that mine was on the lowest speed. He said he had to unattach a wire and attach/screw in a different wire to put the fan speed on high. (He said he attached the black wire, I think.)

Why are there different fan speeds? And, if they are going to offer three different fan speeds, why not just have a three-position switch somewhere inside the unit instead of the technician having to screw in a different wire to change the fan speed. The whole setup just seems weird to me. Why would anyone want their unit's fan set on slow speed if there is a fast speed available anyway. This is for cooling I am talking about, not for heating.

The unit is a Bryant model 582ANW024060AAAD

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Josh O.
Nashville, TN

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Old 06-13-2010, 09:08 PM   #2
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Why do you have to screw in a different wire to change the fan speed?


The same motor can be used for 1) low speed continuous running, 2) heating speed, 3) cooling speed. Motors have different windings to produce different speeds. The AC needs the most speed. Sometimes we use a lower cooling speed to 1) reduce noise, 2) get better dehumidifying 3) if the fan capacity is greater than necessary etc etc. Switches can fail, DIYers can fool with the switch and freezeup and ruin a AC unit etc etc. Liability and warranty reasons for the manufacturer would also be an issue. Where I live we sell most of our furnaces with 3 ton capable blowers and a lot of 2 ton AC units to get better airflow for poor ductwork and want the ability to do so and choose a lower speed if necessary.

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Last edited by yuri; 06-13-2010 at 09:12 PM.
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Old 06-13-2010, 09:17 PM   #3
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Why do you have to screw in a different wire to change the fan speed?


There's different fan speeds so a furnace or air handle can be compatable with several sizes of AC's. If yours has a 3 ton blower then low might have been a better match to the required amount of air then high.
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Old 06-13-2010, 09:32 PM   #4
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Why do you have to screw in a different wire to change the fan speed?


So I need to know how many tons my blower is? The AC unit is 2 ton. How would I find out how many tons my blower is capable of? I guess I'd have to open the unit and look for a label on the blower?
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Old 06-13-2010, 09:38 PM   #5
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Why do you have to screw in a different wire to change the fan speed?


The model number of the air handler of Bryants and Carriers usually has the tons of fan capacity built into it. Ie: 24 = 2 ton, 36=3, 48=4, 60=5
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Old 06-14-2010, 06:32 AM   #6
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Why do you have to screw in a different wire to change the fan speed?


most residential call for hi for cooling and low for heating..if you have a gas furnace the low is controlled thru the limit within the furnace and the hi for cooling is controlled thru the stat...might have a med hi cool option speed but keep that heat at low speed

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