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WildeOne's avatar
WildeOne
Explorer
Jan 04, 2017

Furnace Fan won't turn off, 2004 Alpha 40'

I am a new motorhome owner (8/2016). My furnace's blower would not turn off with the thermostat (blowing air, no heat) so I accessed the main switch through the outside panel to turn it off.

Is there a filter somewhere that could be clogged and causing the safety relay to turn off the heat and keep the fan blowing? I've poured over the book and opened every panel I can find and am confounded.

Thanks for any input.
Class A
  • jplante4's avatar
    jplante4
    Explorer II
    Jan 04, 2017
    Usually there's a switch on the thermostat that says "Fan On/Auto". In Auto, the fan runs with the furnace. In On, the fan runs all the time.
  • Dick_B's avatar
    Dick_B
    Explorer
    Jan 04, 2017
    Could it be that simple as the On/Auto switch position? Let's hope so.
  • zigzagrv's avatar
    zigzagrv
    Explorer
    Jan 04, 2017
    The furnace fan will run after the heat shuts of for a few minutes till everything (ducts and heater itself) cools down. This is normal.

    The switch mentioned above only controls the A/C fan I believe.
  • crasster's avatar
    crasster
    Explorer II
    Jan 04, 2017
    zigzagrv wrote:
    The furnace fan will run after the heat shuts of for a few minutes till everything (ducts and heater itself) cools down. This is normal.

    The switch mentioned above only controls the A/C fan I believe.


    If the heater has lights it should light the "purge" cycle for this - if this is what is happening.
  • Sloop_Smitten's avatar
    Sloop_Smitten
    Explorer
    Jan 04, 2017
    Older furnaces have a time delay relay which sends voltage to the fan. If that goes bad it can cause your fan to run continuously or not at all. On newer furnaces the fan is controlled by a circuit board. We need to know the furnace model and number to provide accurate guidance.
  • tropical36's avatar
    tropical36
    Explorer
    Jan 04, 2017
    WildeOne wrote:
    I am a new motorhome owner (8/2016). My furnace's blower would not turn off with the thermostat (blowing air, no heat) so I accessed the main switch through the outside panel to turn it off.

    Is there a filter somewhere that could be clogged and causing the safety relay to turn off the heat and keep the fan blowing? I've poured over the book and opened every panel I can find and am confounded.

    Thanks for any input.

    Other than having your thermo setting for fan on, were you plugged in and/or were your batteries fully charged?
    If in auto then it sounds like the sail sw. shut off the gas from lack of proper air flow and in which case the temp. setting couldn't be satisfied.
    Hence a continuous run until the batteries are depleted completely.
  • dougrainer's avatar
    dougrainer
    Nomad
    Jan 04, 2017
    tropical36 wrote:
    WildeOne wrote:
    I am a new motorhome owner (8/2016). My furnace's blower would not turn off with the thermostat (blowing air, no heat) so I accessed the main switch through the outside panel to turn it off.

    Is there a filter somewhere that could be clogged and causing the safety relay to turn off the heat and keep the fan blowing? I've poured over the book and opened every panel I can find and am confounded.

    Thanks for any input.

    Other than having your thermo setting for fan on, were you plugged in and/or were your batteries fully charged?
    If in auto then it sounds like the sail sw. shut off the gas from lack of proper air flow and in which case the temp. setting couldn't be satisfied.
    Hence a continuous run until the batteries are depleted completely.


    Except for one very rare Atwood model(usually used on very hi end 5th wheels and park Models and HAS to use the specific Atwood wall tstat) NO furnace blower reacts to the Wall tstat Auto/ON fan switch. The Fan is controlled by the furnace internal controls and will ALWAYS Shut ON and OFF when the heat cycle is complete unless it malfunctions. Doug
  • Clay_L's avatar
    Clay_L
    Explorer
    Jan 04, 2017
    If the high temp cut-off thermodisc switch fails, what you are describing happens. Not the only cause for what you describe and not common but does happen.
  • DrivingMissDais's avatar
    DrivingMissDais
    Explorer
    Jan 04, 2017
    Your heater has entered "lock out" mode. this happens when during the start sequence, a flame is not established in 7 seconds. The blower will run until the thermostat is cycled off. Most common cause is flame sensor, try cleaning and adjusting first, then replace if necessary, it is not an expensive part.
  • dougrainer's avatar
    dougrainer
    Nomad
    Jan 05, 2017
    DrivingMissDaisy wrote:
    Your heater has entered "lock out" mode. this happens when during the start sequence, a flame is not established in 7 seconds. The blower will run until the thermostat is cycled off. Most common cause is flame sensor, try cleaning and adjusting first, then replace if necessary, it is not an expensive part.


    True for OLDER furnaces. Depending on his year and model furnace, he probably has the current control board that shuts the Fan OFF when the flame sequence fails. The models that have this have the Fan relay ON the Ignition module. Doug

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