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My home is heated by a Bryant 359AAV furnace. The thermostat controls and indicates whether the fan is ON or OFF, but the furnace has a four-speed fan. I believe the installer set the fan on "HI" and I would like to turn it down both for quiet and electricity savings. Given the external static pressure, "MED-HI" would still move enough air, and "MED-LO" is only a little out of spec.

I obtained the user's manual and fan speed adjustment is not covered. Then I inspected the furnace circuit board but couldn't tell where the adjustment happens. Then I had two phone conversations with Bryant customer service, who deliberately would not tell me jumper or switch controls the fan speed, ostensibly because of implications for my warranty (I'm not sure if I have one). They want me to call the original installer, or refer another professional.

How can I adjust the fan speed?

Edit: a helpful user found the more technical service manual, which does address the wire colors for each speed.

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  • sounds like poor customer service from Bryant, noted. Look at the ladder diagram for the fan connections. You can switch out the colored wires to route orange instead of black for heat.
    – dandavis
    Commented Mar 27, 2018 at 20:03
  • @dandavis thank you. i will look for that diagram inside the furnace (it's not in the manual).
    – Aaron Brick
    Commented Mar 28, 2018 at 1:22
  • i found it on your link, page 20... follow the wires around the fan and you should see a terminal block with the selection colors (black, orange, blue, red)
    – dandavis
    Commented Mar 28, 2018 at 2:16
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    Bryant will not (and should not) tell you how to make the adjustment over the phone. Without properly evaluating the system, changing the fan speed arbitrarily can damage the system. The fan speed will depend on the amount of resistance in the system, which is different in every installation.
    – Tester101
    Commented Mar 28, 2018 at 2:23
  • @dandavis thanks, I hadn't seen that service manual until just now; i only had the user's manual. Cheers!
    – Aaron Brick
    Commented Mar 28, 2018 at 3:12

2 Answers 2

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When you look at the motor there are 7 wires. 2 brown for the capacitor, a White common wire, Black for high, orange for medium high, blue for medium low and red for low. It comes from the factory with the black plugged into cool and the orange plugged into heat. Blue and red are hooked to M1 and M2 which are just place holders. To reduce speed swap the orange wire with either the blue or red wires on the circuit board. I have to warn you however that low air flow can damage the furnace and actually be less efficient. You should take the temperature at the outlet of the furnace and at the inlet of the furnace. Subtract the two, this will give you your split. Compare that to the required split on the nameplate of the furnace. If it is too high you need more air. I have seen cases where the furnace is too large for the ducts and was overheating even on high speed.

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  • Glad to see you included the temp measurements; if the unit overheats a fire could result. I think sometimes people do not take a moment to consider the engineering reasons behind a certain speed setting. In AC world it just costs you $$ and maybe an early compressor replacement. However with a furnace high heat means things around it get hot, not enough airflow and things burn up - hence if that FAN is not turning - a vane switch or fan speed switch interrupts the heating elements and a DIY'er might just say a bit of duct tape will keep that switch on all the time!!
    – Ken
    Commented Mar 30, 2018 at 8:01
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Adjusting the fan speed for the furnace is not something to do just because you want it quieter or to 'save' electricity.

Your furnace elements have a certain wattage (heat output) and require a proper amount of airflow over them - otherwise they could overheat and start a fire.

So the reason Bryant did not tell you was because they don't want the liability of burning your house down with occupants inside of it!

Think about how your furnace operates - the unit starts the fan and the heating elements and then when the room temperature is reached the elements are turned off and the FAN still runs - too cool down those heating elements - so as not to start a Fire! After the cool down period about 5 minutes or so the fan will turn off.

So unless you know what the airflow ratio is supposed to be, generally a simple method is performed by taking a temperature at the inlet and a temperature immediately after the elements .. there is a temperature change threshold.

FYI: If you insist on adjusting your furnace fan speed - make sure you tell any other occupants you did this so they can stay somewhere safe.

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  • I appreciate your concern.
    – Aaron Brick
    Commented Mar 29, 2018 at 22:10

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