Manual "Fan ON" does not work

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Old 01-24-21, 11:29 AM
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Manual "Fan ON" does not work

When I turn on manual "FAN ON", the fan does not turn on. I hear a "click" at the furnace when the manual fan is trying to turn it on, but the blower motor does not turn on.
I checked voltage between R and C on the main board and it shows 27VAC.
However, when the heat turns on, the fan turns on just fine to circulate the heat throughout the house.
The manual "FAN ON" was working fine up until a few days ago.

Furnace model: YORK TG9S100C20MP11A


Thermostat: Google Nest Learning Thermostat Generation 3
I did a factory reset on the Google Nest Thermostat and still having the same issue with the fan.

Thanks for any help!
 
  #2  
Old 01-24-21, 01:50 PM
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Your furnace uses two blower speeds. One for heating and one for cooling.
I don't know which speed the FAN ON controls. Usually it's the high (cooling) speed.

Go to your furnace board and jumper from R to G and see if the blower runs. Be sure to hold the safety switch in when doing this test or the furnace will be dead.

If it does.... you can try the same thing as the stat. Connect the G wire to R and see if the blower runs.
 
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Old 01-24-21, 02:58 PM
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I jumpered R to G on the furnace board and heard the same "click", but the blower motor still does not run. I didn't try jumpering the wires at the thermostat because based on the result above, it seems the problem is not with the thermostat.

From the wiring diagram, it looks like the high speed is for cooling.

Side note, there are no fault codes blinking on the LED on the control board.
 
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Old 01-24-21, 04:29 PM
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There wouldn't be any codes as it's a blower problem.
It would have to interfere with the heating process to set a code.

Check from HI COOL to neutral to see if you have 120v when the blower should be running.

 
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Old 01-24-21, 06:44 PM
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HI COOL to Neutral does not show 120V when the blower should be running. I hear the "click" and the multimeter goes from around 120mV to 330mV....but not 120V.
 
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Old 01-24-21, 08:31 PM
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That would indicate a defective relay on the control board requiring a board replacement.
 
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Old 01-25-21, 05:56 PM
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Thanks for the troubleshooting Pete! Gonna order a new board and put it in.
 
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Old 01-31-21, 12:01 PM
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Replaced the board and all is working well again! I might even replace/solder in a new relay on the board to have a good spare for the future.

Thanks again!
 
 

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