Adjusting fan speed on direct drive blower

Discussion in 'HVAC Heating & Cooling' started by chrisexv6, Dec 26, 2009.

  1. chrisexv6

    chrisexv6 New Member

    Messages:
    78
    Location:
    Connecticut
    I have a Oneida/Royal LOB oil fired furnace with a direct drive blower. At some point, an AC tech bumped the blower speed to high, because there wasnt enough air flow. Now, Im thinking it was set for heating speed, which is supposed to be different than cooling speed (of course)

    Id like to set it back to a lower heating speed so the furnace will run longer, more efficient, more comfortable (I hate forced hot air! but I dont have a choice)

    Looking at the schematic Im not 100% positive what wire needs to be connected to the "speed lead" for the blower. The blower has 3 speed settings, using a red/blue/black lead. I see a yellow coming off the fan control going to a main junction box. From that box a yellow, black and white come into the blower junction box. White to white, obviously. Schematic shows Black to Blue on blower motor, and Yellow to Black on Blower motor.

    My question is......which lead needs to be changed to get to a lower fan speed? Or, exactly which lead CONTROLS the fan speed.......is it the yellow from the Fan/Limit control?

    If this is clear as mud, I apologize. Ill try to get a pic/scan of the schematic if necessary.

    Thanks in advance.

    -Chris
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
  3. chrisexv6

    chrisexv6 New Member

    Messages:
    78
    Location:
    Connecticut
    Thanks. It helped a little, but I still couldnt figure out what the line voltage input to the blower is.

    See attached image of the schematic on my furnace. On the right are the 3 blower selections.....I have 1 of the 2 bottom ones, both 3 speeds, both with the same colors for the same speeds. Note the white yellow and black leads going into the blower junction box. The black lead is a thin gauge, almost like its from a relay. Yellow and white are the same gauge, almost like they are line voltage and common.

    Any suggestions would be appreciated.

    Thanks.

    -Chris

    [​IMG]
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    The blue lead on the motor is med, and is probably the heat setting. The black lead is hi, and is probably the cool lead. Moving the wire from the blue lead to the red lead would change that setting to medium.

    Without being able to measure air flow, using the wrong blower speed can cause inadequate air flow and you could start to have temp limit issues.
  5. chrisexv6

    chrisexv6 New Member

    Messages:
    78
    Location:
    Connecticut
    "the wire"....does that refer to the yellow wire (looks like line voltage) or the thin black wire (which I cant really tell what it does)?

    I figured it would be the yellow lead, connected directly to the red blue or black leads. But that still leaves the thin black lead coming in from the main j-box as an unknown.
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