Furnace blower does not turn on in the auto position

Discussion in 'HVAC Heating & Cooling' started by vlee1973, Oct 28, 2010.

  1. vlee1973

    vlee1973 New Member

    Messages:
    7
    Location:
    Wisconsin
    The furnace lights up, but the blower will not turn on if I have the thermostat in the auto position. The blower will turn on if I turn the thermostat to the fan position. I have Ultra II 90 high efficiency furnace
    maid by Magic Chef. Any help would be greatly appreciated.

    Vince
  2. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    The blower comes on in the auto mode based on time or on duct air temperature.
    If it doesn't come on I hope the hi temp limit switch kicks out? Otherwise you are in danger.

    Can you post a schematic? Do you have a multimeter?
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    There is a temp. sensor which delays blower start until the heat exchanger warms up. Need to replace that sensor, or possibly the fan control relay board.
  4. vlee1973

    vlee1973 New Member

    Messages:
    7
    Location:
    Wisconsin
    Sorry about the wait guys. The furnace does turn off after a couple of min. I could get my hands on a multimeter. I have added a couple of pictures.

    Attached Files:

  5. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    So your hi limit switch works.

    The schematic is illegible but if it weren't there would be some crucial circuit test points you could check. My camera has a close up option but this same schematic may be online somewhere.

    You should probably find out why your furnace housing is rusting. Maybe water is dripping from that blower housing in the upper left.
    Last edited: Oct 29, 2010
  6. vlee1973

    vlee1973 New Member

    Messages:
    7
    Location:
    Wisconsin
    I changed the temp sensor and everything is working like a champ. I will look into the rusting problem. Thank you for all of the help Jimbo and Thatguy.

    Vlee
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