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I noticed on our Carrier furnace that the blower motor and fan come on when the heat is called for like a minute, then it shuts completely off before the gas and heat and blower motor take off to heat the house. What is the purpose of the blower motor and fan coming on and shutting off before the heating starts? I am replacing my shot blower motor and feel this function is causing the motor to wear out prematurely.

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    Is the blower running while the heat is on i.e. does it start up again? – JimmyJames Feb 4 at 16:17
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    Model # of furnace? – manassehkatz Feb 4 at 16:21
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    Does the heating ever start? Usually there is a blinking LED on the control board that tells you what the problem is. This may be that it detected the burners didn't light and then turned the fan off. Like the other comment said, it is normal for it to come on for a few seconds before the burner lights, but it should be followed by the burner lighting and blowing hot air. – Ron Beyer Feb 4 at 16:46
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    My furnace always resets the blower to off before starting a heat cycle. With either a timer or manually turning on the blower, if at some point there is a call for heat it shuts the blower off before doing the "start and confirm power exhaust, fire and confirm burners, start blower" process. I assumed it was a safety process, so the first parts of the startup can check for exhaust, fuel flow, ignition, etc. before trying to fill the house with combustion gases. – user96678 Feb 4 at 17:01
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    (That being said, I don't know why a call for heat would cause it to start/stop/start the blower. Unless this model has a sensor on the blower and will only work if it knows it can actually blow heat past the exchanger. The stop and start afterwards, though, seems consistent with my own experience. A look at the manual for this model might solve the mystery.) – user96678 Feb 4 at 17:12
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Contrary to JPhi's comment, it is not normal for the "air" to come on for a bit before ignition of the burner. What Ms. Diaz may have been hearing is the combustion air blower coming on, a failed ignition attempt and then shutdown. That is not the blower motor "air" coming on first. Ron Beyer had it right. Check the error code.

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Are you perhaps hearing the inducer motor turning on? Usually the furnace blower would only come on once the burners have ignited and the temp sensors get to the level in which it tells the blower to turn on and blow air into the house. Same with the end of the cycle. The blower will continue to run after the thermostat call for heat has been satisfied to "cool" the system and keep it from overheating. You might be hearing the inducer motor, and once the system ignites and the main blower comes on, you don't hear the inducer because the main blower is louder and blowing harder.

Now, if you are feeling cold air from the vents, and the furnace is not igniting, you could have a mainboard issue.

If you have a smart thermostat, and set it up to control the blower from the thermostat instead of the equipment, then the thermostat is turning the fan on after a preset time, that will blow cold air, then the furnace burners ignite, the temp sensor clicks over and confuses the thermostat and then takes over the blower operation. Sometimes this will even prevent the burners form igniting as the blower is blowing to hard for the pilot to stay lit. If this is the case, go through the setup of the thermostat and switch blower control from thermostat to equipment. I had this issue when I first installed my Ecobee 4. Once I figured out what was happening, I found the setting was set to thermostat as default. Once I switched it to equipment, the bower functions as it should.

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