furnace wont work on auto fan


  #1  
Old 11-11-10, 04:32 PM
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furnace wont work on auto fan

have replaced fan relay..and fan control unit also changed thermostat still runs with fan on but fan wont run on auto
 
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Old 11-11-10, 05:14 PM
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Can you tell us the number and color of all the wires that come out of the CB blower? If multiple wires, which you likely have (you might have up to 7 or 8, not counting the green ground wire) we need to see if current is getting to the board connection where the AUTO speed terminal is (which may say HEAT onthe board), and if the motor winding for the speed the motor uses on AUTO, is good.
 
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Old 11-11-10, 06:01 PM
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if i change blower speed on auto will fan come on im not at rental and cant get there till tomorrow ...thanks
 
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Old 11-11-10, 06:29 PM
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Yes, you can do the swap no problem. Then you will learn something, if it works or not. But you have to make sure it is a speed wire that may be on a current board "Park" setting or on COOL terminal,and NOT the green(ground), white(neutral), or brown wires(capacitor) from the motor! The remaining 3 or 4 wires are for speeds, and may be colors like blue, black, yellow and red. There should be a legend in the wiring diagram telling you which color is what speed, and may or may not also be listed on the motor itself.
 
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Old 11-11-10, 07:02 PM
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thanks will try tomorrow and let you know,,,,,im getting frustrated
 
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Old 11-15-10, 06:53 AM
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moved fan speeds to med lo and low...they were on med hi and hi ..furnace still ran same way ..only with fan on....could it be the main circuit board..hate to buy another part without knowing....its getting cold in omaha thanks for your help
 
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Old 11-15-10, 05:00 PM
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Then you are not getting power at the terminal where the blower wire attaches to the controlboard, perhaps labled there as HEAT.

Just so you can get heat for now, why aren't you running the furnace when fan is set to ON? The fan will run all the time, but that won't hurt anything. Some people even choose to run it like that.
 
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Old 11-15-10, 05:55 PM
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house is empty for the moment...so heat is off for now....it gets down to 50 at night....i need some advice as to what i should do next..review ..replaced therm....fan limit ..fan relay...next step control module...any more options or suggestions...
 
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Old 11-16-10, 03:25 PM
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In auto, do the burners come on?
 
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Old 11-16-10, 08:44 PM
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yes but they go off when furnace overheats....comes back when temp goes under limit,,thanks for reply
 
 

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