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    jonwilliam's Avatar
    jonwilliam Posts: 31, Reputation: 1
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    #1

    Feb 15, 2009, 02:23 PM
    Old lennox with standing pilot and cam stat cycling
    Hi gents

    Old lennox model 9803-980-2 H.boy 68000 BTU with a honeywell fan limit cycling every 5minutes . The wires disconnected at the Stat and jumpered . Still the furnace acting same problem . The motor and blower wheel and pilot acting quite normal . Do you think the fan limit is faulty or any other ideas please and tks you
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #2

    Feb 15, 2009, 02:33 PM
    What is cycling every 5 minutes - the heating cycles, or just the blower? If it is the blower, the CamStat fan/limit combo has likely lost its differential capability.
    jonwilliam's Avatar
    jonwilliam Posts: 31, Reputation: 1
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    #3

    Feb 15, 2009, 04:00 PM
    Quote Originally Posted by KC13 View Post
    What is cycling every 5 minutes - the heating cycles, or just the blower? If it is the blower, the CamStat fan/limit combo has likely lost its differential capability.

    Hi KC13
    Thanks for your quick response .
    No actually the burners keeps firing however the blower keeps cycling every 5 inutes
    And am sorry the fan limit is Honeywell but not Cam Stat . So according to your description , the fan limit go to be replaced am I right?
    Thanks again
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #4

    Feb 15, 2009, 04:05 PM
    Are you sure the fan is cycling via the combo control, and not because it is overheating? Try this: If the thermostat has a fan switch, set it to the "ON" position. Does the fan run continuously? If so, the motor is o.k.
    jonwilliam's Avatar
    jonwilliam Posts: 31, Reputation: 1
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    #5

    Feb 15, 2009, 04:29 PM
    Quote Originally Posted by KC13 View Post
    Are you sure the fan is cycling via the combo control, and not because it is overheating? Try this: If the thermostat has a fan switch, set it to the "ON" position. Does the fan run continuously? If so, the motor is o.k.
    Well there is a push in and pull out button on the honeywell fan limit that gets it to Auto and On . I pushed it over to On that means goes continuously and sure enough it did .
    Yes am positive about the motor that is working fine .
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #6

    Feb 15, 2009, 04:36 PM
    With the cover removed from the fan/limit combo, you should see the adjustable stops on the dial face for the fan off (lowest) and fan on (middle) settings. Where are these set?
    jonwilliam's Avatar
    jonwilliam Posts: 31, Reputation: 1
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    #7

    Feb 15, 2009, 04:58 PM
    Quote Originally Posted by KC13 View Post
    With the cover removed from the fan/limit combo, you should see the adjustable stops on the dial face for the fan off (lowest) and fan on (middle) settings. Where are these set?
    90 fan on 150 fan off 200 shut down
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #8

    Feb 15, 2009, 05:08 PM
    Quote Originally Posted by jonwilliam View Post
    90 fan on 150 fan off 200 shut down
    90 is fan off, 150 is fan on. Observe the dial with the heat running. The blower should start when the dial reaches 150 and stop when the dial reaches 90. It should stabilize somewhere in between the two with burners running. If it doesn't, either the fan control is bad or the gas input is too low to maintain proper heat exchanger temperature.
    jonwilliam's Avatar
    jonwilliam Posts: 31, Reputation: 1
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    #9

    Feb 16, 2009, 05:45 AM
    Quote Originally Posted by KC13 View Post
    90 is fan off, 150 is fan on. Observe the dial with the heat running. The blower should start when the dial reaches 150 and stop when the dial reaches 90. It should stabilize somewhere in between the two with burners running. If it doesn't, either the fan control is bad or the gas input is too low to maintain proper heat exchanger temperature.
    Thanks you so much for the response I will make sure to follow up your comments .
    Thanks again
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