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Electronic fan and limit controller

JjEjFjF
JjEjFjF Member Posts: 4
edited January 2019 in Thermostats and Controls
Is there such a thing as an electronic fan and limit controller for a furnace as opposed to the standard honeywell bi metal controller ?

Comments

  • HVACNUT
    HVACNUT Member Posts: 4,592
    Yes but not a direct replacement.

    Most furnaces now use disc limits, a circuit board with a time delay relay for fan control in the board or a separate exterior TDR.
    A disc limit wont have the insertion depth of a fan/limit so altering a factory location is not a good idea.

    Nothing that I know of is an upgrade and uses the factory fan/limit location.
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,689
    A better question is...what problem are you experiencing?
    The bi metal fan/limit has been around for over 50 years. Very reliable/durable. Probably replaced less than 12 in almost 30 years, can't even remember the last time.
    But I've replaced many of the other types.
    steve
    ratio
  • JjEjFjF
    JjEjFjF Member Posts: 4
    STEVE , Im in PA also...just sayin. Its not so much a problem as it is a annoyance. This fan/limit controller is on a coal stove/furnace. I keep the fan on and off set pretty low as compared to a regular furnace. On at about 145 and off at around 90. Reason being is because the furnace will go to low flame when not called for heat. The internal temp will get to about 145-150 at idle. I can pretty much keep my house warm with the flame at idle if its not real cold outside so why not take advantage of that heat instead of letting it just go out the chimney. The manufacturer recommends setting the ON temp at 160 to prevent the fan from kicking on during idle. Again, i want to take advantage of that "wasted" heat. Anyhow.....with the OFF set at 90 , and the convection blower blowing , approaching the shut off temp ,on occasion the fan control will shut off the blower but not fully switch off at the fan control. Sort of like balancing a light switch between on and off. The light might go off but technically the switch is not off. I hope that makes sense. Then after a few seconds or so when the heat builds up in the furnace a few degrees , the blower will come back on for 5 or 10 seconds gaining enough momentum to actually switch the controller off. I know it sounds crazy but i had it happen with 2 different controllers. Simply setting the OFF temp to 105-110 seems to have solved the annoyance.All is good but i thought if they made some kind replacement electronic controller , this type of thing couldnt / shouldnt happen. Again, its an annoyance that was pretty much resolved yet it doesnt hurt to look around to see whats out there.
  • JjEjFjF
    JjEjFjF Member Posts: 4
    HVACNUT said:

    Yes but not a direct replacement.



    Most furnaces now use disc limits, a circuit board with a time delay relay for fan control in the board or a separate exterior TDR.

    A disc limit wont have the insertion depth of a fan/limit so altering a factory location is not a good idea.



    Nothing that I know of is an upgrade and uses the factory fan/limit location.

    Thanks for your input.
  • HVACNUT
    HVACNUT Member Posts: 4,592
    edited January 2019
    Knowing it was a stove furnace, well... Having the fan cycle on once or twice after demand is typical to get those unused BTU's out to the living space. As you've done, raising the off marker worked.
    You could install a DOB time delay to the motor if it's safe to do.
  • JjEjFjF
    JjEjFjF Member Posts: 4
    edited January 2019
    HVACNUT I understand what youre saying but the fan/limit doesnt fully (click) off. The temp will lower and just touch on the OFF marker making the blower shut off without fully switching (click) the fan/limit off. Therefore any heat build up will immediately turn the blower back on without having to travel all the way up to the ON marker.
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,689
    I think it's working like it should, based on the parameters you have it set. Maybe it doesn't like that 90° setting.
    Does it do it if you bump it up 10 degrees?

    I don't see another standard product around that would do what you want.

    If it's idling, I assume the temperature inside the plenum is rising? So a higher setting would just turn the fan on when it's a little warming.

    I'd pull it out and make sure it's clean (power off of course). A small brush on the sensing side.
    steve