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Old 01-20-2013, 09:16 PM   #1
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High limit switch


I have a concord 80 plus gas furnace. It is making a buzzing noise. and the red light is blinking four times indicating the high limit switch is on. Is there anything I can do to fix it myself?

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Old 01-20-2013, 09:38 PM   #2
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High limit switch


Sure can. Limits trip because the unit has gotten too hot due to lack of air flow. That could be from a dirty filter,a dirty evap coil, a bad capacitor on a blower motor, a bad motor or a bad control board not sending voltage to the motor.

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Old 01-21-2013, 01:50 PM   #3
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High limit switch


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Originally Posted by Marty S. View Post
Sure can. Limits trip because the unit has gotten too hot due to lack of air flow. That could be from a dirty filter,a dirty evap coil, a bad capacitor on a blower motor, a bad motor or a bad control board not sending voltage to the motor.
Or the limit itself could be bad. However the buzzing you're hearing may be the motor attempting to run, which would lead me to believe the problem would be the motor or the capacitor. Easiest way to check is to turn on the fan, carefully reach back and feel if the fan is vibrating and getting hot. You can attempt to spin the motor (again be careful), if it starts & runs normally after you kick start it, the capacitor is probably the cause.

The capacitor is also going to be the cheapest and easiest to replace, so if I was unsure I'd try that first. You can take the old one out & take it to a parts warehouse so they can match the one you need. (you have to have a specific microfarad rating for different motors) There are 2 wires going into it, you don't have to worry about switching them, so it's an easy fix.
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