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NorthwestBound's avatar
NorthwestBound
Explorer
Dec 06, 2016

Suburban sf-30 furnace noise after shutting down

After swapping out my converter because my old Magnetek converter wasnt outputting enough voltage for the furnace to get up to speed to trigger the sail switch, i've been hearing an electronic sound after the thermostat reaches the set temp and shuts down the furnace.

The furnace operates normally as well as the thermostat which i changed out yesterday for a Honeywell digital programmable. The sounds were occuring before the Tstat change.

So, the furnace shuts down, and an electronic constant noise is coming from the furnace. It stays constant for a minute, then goes intermittent, then goes away altogether. If i can record it i will. But i hope its not a sign that im gonna have throw more money at this 5th wheel.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Dec 06, 2016
    NorthwestBound wrote:
    Old-Biscuit wrote:
    Fan continues to run after flame is shut off to cool heat exchanger...can run 30-90 seconds

    Is that the 'noise' you are hearing???


    No, the fan has already come to a stop. Your not able to hear it until the fan is completely stopped.


    OK.....

    Then it sounds like the 'timed delay relay' buzzing

    This is the device that allows fan to run prior to main flame lighting and after main flame has shut down.

    It is a bi-metallic coil that gets energized when t-stat contacts make up and then power comes off when t-stat contacts open.....coil then cools off which then shuts-down fan power

    Timed delay relay is first component energized in system and the last to loose power.
  • westend's avatar
    westend
    Explorer
    Dec 06, 2016
    Typically, when thermostat has been satisfied that temperature has reached setpoint, there is no power available to furnace. When you replaced the thermostat there may still exist a constant power to part of the furnace.
    A meter on the furnace circuits may diagnose this condition. Probes placed on the limit switch is where I would be looking. You may also have a wonky limit switch but I don't know if that would cause an "electronic noise" as you have described.
  • NorthwestBound's avatar
    NorthwestBound
    Explorer
    Dec 06, 2016
    The batteries are potentially bad. Had Interstate test them, and they said they were good, but they dont hold a charge well.

    Thats all in a previous post. For now, the converter is putting a steady 13.6v to everything and the furnace seems to work as designed. Its just this weird noise that worries me.
  • NorthwestBound's avatar
    NorthwestBound
    Explorer
    Dec 06, 2016
    Sam Spade wrote:


    This might have been an incomplete diagnosis of the problem.
    The BATTERY should have gotten the fan up to speed.

    BUT....if the converter had been bad for a long time it might have left the battery in a discharged state long enough so that you need a new battery now too.

    Are you sure this noise is really coming from the furnace and not the new converter ?


    Certainly not the converter. Last night i was in the basement with the converter till the fan quit and it was definately coming from the furnace. Ive pulled the outside cover off but theres nothing but fan motor to access from there.
  • NorthwestBound's avatar
    NorthwestBound
    Explorer
    Dec 06, 2016
    Old-Biscuit wrote:
    Fan continues to run after flame is shut off to cool heat exchanger...can run 30-90 seconds

    Is that the 'noise' you are hearing???


    No, the fan has already come to a stop. Your not able to hear it until the fan is completely stopped.
  • Sam_Spade's avatar
    Sam_Spade
    Explorer
    Dec 06, 2016
    NorthwestBound wrote:
    After swapping out my converter because my old Magnetek converter wasnt outputting enough voltage for the furnace to get up to speed to trigger the sail switch,


    This might have been an incomplete diagnosis of the problem.
    The BATTERY should have gotten the fan up to speed.

    BUT....if the converter had been bad for a long time it might have left the battery in a discharged state long enough so that you need a new battery now too.

    Are you sure this noise is really coming from the furnace and not the new converter ?
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Dec 06, 2016
    Fan continues to run after flame is shut off to cool heat exchanger...can run 30-90 seconds

    Is that the 'noise' you are hearing???

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