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  1. #14
    Join Date
    Jan 2010
    Posts
    6,058
    Quote Originally Posted by georgelass View Post
    The schematic said the heater was not on all units. But it didn't say it was optional on
    the units that had it. Because in my experience my assumptions have often coincided
    with screw-ups, I did not want to assume that the heater was optional for the furnace
    models that had them installed at the factory. Often what sounds logical to me
    usually has some loophole that I didn't consider. I try to be more cautious about
    winging it these days.
    Sounds like someone speaking from experience.

  2. #15
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,366
    Quote Originally Posted by georgelass View Post
    The schematic said the heater was not on all units. But it didn't say it was optional on
    the units that had it.
    I emailed you the install manual on this unit. It states the approx. temps the fan should turn "ON" and "OFF".
    Instead of learning the tricks of the trade, learn the trade.

  3. #16
    Join Date
    Jan 2010
    Posts
    6,058
    Quote Originally Posted by rundawg View Post
    I emailed you the install manual on this unit. It states the approx. temps the fan should turn "ON" and "OFF".
    rundawg,
    Do you have any info on that heater type limit ?
    Thanks,
    VTP

  4. #17
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,701
    Name:  fan_limit_control_with_text.jpg
Views: 1332
Size:  28.8 KB

    this was the last fan limit used on Lennox furnaces before they switched to blower control boards in the G20 furnaces.
    heater brought the fan on sooner than the normal fan setting in the control, more for efficiency than safety.

  5. #18
    Join Date
    Feb 2004
    Posts
    2,458
    Wrong terminology used here. It is not a heater for the LIMIT. Camstat was one of the mgf's. They had 6 wire controls and 4 wire controls. Lennox and DNP used them several years ago, before boards were common. 4 wire was fan only, 2 wires were 120 volt for blower, other 2 wires were 24 volt heat assist. When the burner came on the heat assist was energized and the small resistance wiring around the bimetal got warm and closed the switch before the furnace temp would. These especially good for an area that was cold and would pull in thru the return.. That would prevent any blower short cycling due to cold air over fan switch. The other control had 6 wires, the 4 mentioned above and 2 for the limit.

  6. #19
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Quote Originally Posted by t527ed View Post
    Name:  fan_limit_control_with_text.jpg
Views: 1332
Size:  28.8 KB

    this was the last fan limit used on Lennox furnaces before they switched to blower control boards in the G20 furnaces.
    heater brought the fan on sooner than the normal fan setting in the control, more for efficiency than safety.
    Yep, that's what it looks like.

  7. #20
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,366
    Quote Originally Posted by VTP99 View Post
    rundawg,
    Do you have any info on that heater type limit ?
    Sent you an email.
    Instead of learning the tricks of the trade, learn the trade.

  8. #21
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,712
    Honeywell makes still makes that fan limit. L4064W. You'll have to go back and find out the insert length.
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    How many times must one fix something before it is fixed?

  9. #22
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,799
    If your supplier does not have the Honeywell, Camstat still makes them. I personally feel the Honeywell product is the better option though. I don't see any safety concerns with using a 4 wire F/L control without the heat assist. I say use what you have. As mentioned earlier, the customer may even be pleased with the warmer air coming out of the registers when the unit first starts.
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
    Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii

  10. #23
    Join Date
    Feb 2004
    Location
    Ontario
    Posts
    700
    We called those "assured fan controls". As said they will bring the blower on quicker, and will maintain heat in the control through the run cycle so the blower will run a bit longer on shut-down and not recycle back on from residual heat. I recall a couple of furnaces that used them had drum style heat exchangers and the control was located where it would be very slow to pick up the heat when the burner was on no matter how finely you'd try to adjust the control, unless you used the "assured" control. You might wait several minutes for the blower to come on. Also one Lennox horizontal model in particular would trip on limit immediately after the blower came on if you didn't use the "assured" control. You can probably get away with not using the proper one without problems, but it's there for a reason. And I recall several times upgrading to an "assured" fan control as a way to solve nuisance cycling problems.
    Question authority!

  11. #24
    Join Date
    Dec 2007
    Posts
    4,668
    Quote Originally Posted by mike3 View Post
    Wrong terminology used here. It is not a heater for the LIMIT. Camstat was one of the mgf's. They had 6 wire controls and 4 wire controls. Lennox and DNP used them several years ago, before boards were common. 4 wire was fan only, 2 wires were 120 volt for blower, other 2 wires were 24 volt heat assist. When the burner came on the heat assist was energized and the small resistance wiring around the bimetal got warm and closed the switch before the furnace temp would. These especially good for an area that was cold and would pull in thru the return.. That would prevent any blower short cycling due to cold air over fan switch. The other control had 6 wires, the 4 mentioned above and 2 for the limit.
    thanks for clarifying it for me, too.

    I never had it explained like this and now I will look at it differently.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  12. #25
    Join Date
    Dec 2007
    Posts
    4,668
    Quote Originally Posted by jetstream View Post
    We called those "assured fan controls". As said they will bring the blower on quicker, and will maintain heat in the control through the run cycle so the blower will run a bit longer on shut-down and not recycle back on from residual heat. I recall a couple of furnaces that used them had drum style heat exchangers and the control was located where it would be very slow to pick up the heat when the burner was on no matter how finely you'd try to adjust the control, unless you used the "assured" control. You might wait several minutes for the blower to come on. Also one Lennox horizontal model in particular would trip on limit immediately after the blower came on if you didn't use the "assured" control. You can probably get away with not using the proper one without problems, but it's there for a reason. And I recall several times upgrading to an "assured" fan control as a way to solve nuisance cycling problems.
    so does the assured control act like a sequencer when the call for heat is lost, in other words after X amount of time that portion of the control is open and now just residual heat activates the fan?

    if so, does it really help on the cool down or just for initial start for those cold short cycle instances?

    thanks.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  13. #26
    Join Date
    Dec 2007
    Posts
    4,668
    found this and answered my questions.

    http://www.honeywell.com/sites/servl...4-73BD77880C46
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

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