fan limit switch adjustment

Old 10-11-02, 09:25 PM
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fan limit switch adjustment

Hi Tom & Co.

I have been able to fix my recent blower problem by replacing the flame sensor, but by studying its operation, I would like to know how the fan limit switch operates to turn on my fan earlier. It takes about 90 seconds to turn on the fan after the burners ignite and the burner turns off very soon after.
This one is made be Honeywell on a Trane Electric Ignition Gas Furnace circa 1988.
It has 3 slider controls and one fixed one. I have searched the web to find adjustment info but have not found out which slider controls are for the off and on of the blower function.
From counter-clockwise which one is on, which is off, what does the fixed one do, and I asume, the last one is an override high temp shut off.
I would like to run the fan for longer in the cycle and I hope you can tell me how to set a better adjustment by learning how these sliders work.

Thank You, Keithap.
Old 10-12-02, 05:16 PM
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Location: NW atlanta
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fan limit switch

is a safety device, yours is 14 yrs old. i would replace it. sounds like you may be describing a "camstat", not sure. of the three settings lowest is fan off, middle temp brings fan on when bonnett temp rises to setpoint, and high temp setting breaks power to the gas valve (basically). am sure these numbers are on the net somewhere, i do not have them on hand, and with something like that i would not guess.

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