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  1. #1
    Setting Up Camp
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    Force furnace fan to run continuously?

    In my 21bhe, my thermostat has the following modes to include fan, cool low, cool high, cool auto and heat. Cool auto cycles the blower on and off with the AC compressor. Cool low and cool high maintain a continuous blower operation as the compressor cycles on and off based on temperature. I am after that constant background noise that the continuous running of the fan provides as well as keep more even heat distribution through increased air circulation. Short of installing another thermostat to force the roof unit to run the fan continuous, has anyone been able to mod the furnace to provide continuous fan operation in spite of furnace cycling on and off?
    -Rob M

    2021 Imagine XLS 21BHE "Wanda Travelmor"
    Everything we wanted in a trailer, nothing we didn't.

  2. #2
    Setting Up Camp
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    Quote Originally Posted by rmaly76 View Post
    In my 21bhe, my thermostat has the following modes to include fan, cool low, cool high, cool auto and heat. Cool auto cycles the blower on and off with the AC compressor. Cool low and cool high maintain a continuous blower operation as the compressor cycles on and off based on temperature. I am after that constant background noise that the continuous running of the fan provides as well as keep more even heat distribution through increased air circulation. Short of installing another thermostat to force the roof unit to run the fan continuous, has anyone been able to mod the furnace to provide continuous fan operation in spite of furnace cycling on and off?
    I also want to be able to force the furnace fan continuously on sometimes, for temperature stabilization and to force heated air into the underbelly. My camper has two Furrion a/c units and a Suburban furnace. The main a/c unit thermostat also controls the furnace. I can run the a/c blowers continuously at high or low speeds, but don't believe that feeds airflow into the underbelly. Any known way to set furnace fan to continuously on mode? Also, where's the air return for the furnace on a 2021 2670MK? Thank you!
    PapaD & GrandAnna
    2021 Imagine 2670MK
    2021 Silverado 2500 LTZ, 6.6 Duramax, Allison 10

  3. #3
    Site Team traveldawg's Avatar
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    gosh, this is a good idea (running the fan constantly to move air). But short of wiring a switch directly the fan motor in the furnace I don't see how else to do it. I don't know of any RV furnace that offers the option to run the fan continuously (like on the air conditioner systems).
    Larry
    2018 F350 SRW SB - AirLift 5000 w/Wireless One; ForScan; 37gal RDS Fuel Tank; Demco Hikacker
    2019 310GK-R - Sailuns; MorRyde SRE4000; Disc Brakes (StopYourTrailer.com); Electric Cord Reel


  4. #4
    Setting Up Camp
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    Thanks for replying. I kinda figured as much, but it never hurts to ask. Since last March, new to RVing, but am learning every day. Your idea for a discrete fan switch is a good one; will look into that, even if it requires an add-on fan to push air through the furnace vent loop without messing with the oem circuitry. Still trying to figure out where the furnace air return inlet is, but I'm in storage till spring. Thanks again!

  5. #5
    Fireside Member
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    Quote Originally Posted by traveldawg View Post
    gosh, this is a good idea (running the fan constantly to move air). But short of wiring a switch directly the fan motor in the furnace I don't see how else to do it. I don't know of any RV furnace that offers the option to run the fan continuously (like on the air conditioner systems).
    My previous camper did have the option to run the furnace fan continuously. We often did exactly what you want to do. We would heat the whole camper with one of those ceramic heaters. I planned on figuring out how on my 337 just haven't found the time. The thermostat was one from a bricks n sticks which may be the key.
    2022 337RLS & 2017 CTD Ram long bed
    425w of solar & Victron system monitors
    GC2 batteries (for now) & 2500w PSW
    Lots of other mods too....

  6. #6
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    I had a plan to do this on my Imagine 2250. I used the fireplace to heat the trailer, but it wouldn't heat the underbelly. I had schematics drawn that would incorporate a remote temperature sensor in the underbelly which would come on at 32 degrees and shut off at 38. Then connect the output of the sensor to a relay which would directly turn on the furnace's blower motor, bypassing the thermostat and electronics of the furnace. Unfortunately, I sold the trailer to my son before I got an opportunity to implement it.

  7. #7
    Site Team traveldawg's Avatar
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    Quote Originally Posted by BigDinMB View Post
    Thanks for replying. I kinda figured as much, but it never hurts to ask. Since last March, new to RVing, but am learning every day. Your idea for a discrete fan switch is a good one; will look into that, even if it requires an add-on fan to push air through the furnace vent loop without messing with the oem circuitry. Still trying to figure out where the furnace air return inlet is, but I'm in storage till spring. Thanks again!
    I'm pretty sure the furnace would have to be removed so you could get inside it and make the necessary wire connections. It would probably just be to put another 12v input to the fan motor (sort of in parallel to the existing circuit).

    I suppose another option is to put a fan in one of the furnace vents and force air back into the furnace plenum which would then force the are out the other vents including those in the underbelly.

    Or install another "vent" on one of the unused furnace plenum outlets and use it to force are back into the furnace's plenum and then out the other vents.

    or.... do what I do... set the furnace at some low temp, presumably at the point your other heating system can't keep the inside of the RV warm and just let the warm air from the furnace do its thing.

    In our case that temp is about 60 to 63 degrees inside temp. At that point our small space heater can't keep up so the furnace comes on to supplement the space heater. We don't run our fireplace at night when sleeping but I'm pretty sure lots of folks do.
    Larry
    2018 F350 SRW SB - AirLift 5000 w/Wireless One; ForScan; 37gal RDS Fuel Tank; Demco Hikacker
    2019 310GK-R - Sailuns; MorRyde SRE4000; Disc Brakes (StopYourTrailer.com); Electric Cord Reel


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