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Old 12-28-2010, 10:52 AM   #1
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problem with furnace will not turn on or works by itself


Last night my furnace started to have" mind of its own",
I have york 25 year old gas furnace
new thermostat has been installed a year ago, new filter is in,
basically the gas burner activates and it is control by limit fan switch with dial system, I can see it turns and it turns on and off the burner when reaches certain temperature, but will not turn the fan on
I can't activate fan by turning fan ON on thermostat and on limit fan switch it will not run
after 10-15 minutes the fan comes on its own and then burner kicks in and it runs ~20 seconds and fan turns off
I have put the previous thermostat doesn't change
I measure voltage on transformer side it has ~27volts, I have check the limit fan switch and on load limit side is 27 volts on fan has 120 volts
so I suspect it motor capacitor bad or motor or limit fan switch bad
I can hear and see motor running but sounds like running on low setting , any ideas ?

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Old 12-28-2010, 11:13 AM   #2
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problem with furnace will not turn on or works by itself


If it is running too slow then the capacitor may be weak, at that age the motor is probably worn out too. Rarely do capacitors fail as the motor usually takes them out/damages them or fails first from age. If your meter measure capacitance then discharge the cap and test it. If not they are cheap and replace it. If it fails soon then the motor is going too.

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Old 12-28-2010, 12:30 PM   #3
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problem with furnace will not turn on or works by itself


Quote:
Originally Posted by yuri View Post
If it is running too slow then the capacitor may be weak, at that age the motor is probably worn out too. Rarely do capacitors fail as the motor usually takes them out/damages them or fails first from age. If your meter measure capacitance then discharge the cap and test it. If not they are cheap and replace it. If it fails soon then the motor is going too.
Thank you,
probably the capacitor and motor are going, one thing I notice once I turn off furnace off and left it sit for an hour and then turn back on, everything seems to start working fine I was able to turn the fan on and off, and seems to work but then it starts again the same cycle, I bought the limit switch but it didn't help, nobody has the capacitor
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Old 12-29-2010, 03:36 PM   #4
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problem with furnace will not turn on or works by itself


Furnace is back online , it was bad capacitor , which cause the blower motor to overheat and shutdown , thou I ordered new motor with capacitor just in case this one fails, but it has been running for over an hour and motor is cool to touch before was v.hot ..

thanks for leads.
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