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Old 12-08-2010, 07:38 PM   #1
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Sometimes air handler fan not coming on in "AUTO"


Hi everyone. New here and hoping to get some help. The problem I am having is that sometimes in "Auto" mode, the air handler blower fan doesn't run. Thermostat calls for heat, the furnace starts and the pipes are hot. The problem is that the blower fan doesn't start by itself if I set the fan to "Auto" mode. The problem doesn't always happen and it seems to happen more in the mornings. Initially I suspected that the problem may be with thermostat but replacing the thermostat did not help. If I turn it to the "FAN ON" position it works great but fan will not kick in automatically the "FAN AUTO" position. What should I do?

I called the oil company HVAC tech and when he came everything was working and he was not able to see the problem. Was charged $90 for the visit. I am hoping someone can help me here.

The air handler is made by FirstCo and is about 10 years old.

Model is 24MBXR-3HW

Fan coil Unit 27JF

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Old 12-08-2010, 08:13 PM   #2
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Sometimes air handler fan not coming on in "AUTO"


Check the capacitor and blower fan terminals.

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Old 12-08-2010, 08:27 PM   #3
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Sometimes air handler fan not coming on in "AUTO"


there is probably a relay in the AH. The relay may be on a control board, or not. It may be failing. trace your wires back from the blower motor and find what they go to.
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Old 12-09-2010, 10:56 AM   #4
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Sometimes air handler fan not coming on in "AUTO"


yea sounds like the relay or fan switch going out. if its a fan switch check the setting on it to see when the fan is suppose to come on. if its a relay on the control board you have to replace the board to fix it.
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Old 01-06-2011, 09:35 PM   #5
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Sometimes air handler fan not coming on in "AUTO"


Problem did not happen for 3 weeks and it started happening again.

I am a new home owner and I have little experience doing this kind of work.

What is the best way to check the fan switch? Is this the part (safety switch) that gets pushed inside when the blower cover is in place?

Is changing the board a DIY job? How difficult is it?
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