fan won't automatically turn on with furnace

[jaristotle]

My fan won't automatically turn on when the furnace kicks on. However, the fan still works as I can flip the FAN switch from AUTO to ON on the thermostat. So both the fan and furnace both work, just not together. Is this a simple fix? Thanks.

Ryan

[LazyPup]

When an HVAC system is run on AC the fan starts immediately. On heat it is customary to provide a delay to insure the plenum is preheated before starting the fan to prevent a blast of cold air.

Look on the inside of the service panel cover and you should find your wiring schematic. From the schematic you will be able to tell if you have a delay on start timer or a temperature sensor in the heat plenum.

If it is a sensor in the heat plenum it may have a manual reset button.

If not, the problem is either in the timer or sensor or you may have a second fan relay for heat.

[Hube]

Your problem is most likely a faulty fan Relay, or in the fan control itself.

[jaristotle]

Thanks for the response. I forgot to mention this earlier, but before this happened, I noticed that sometimes the fan would try to turn on, but it would take repeated attempts for it to click on. So essentially it would click on and off several times before it finally turned on. Now it doesn't come on at all unless I manually turn it on via the thermostat.

Does this make it even more likely that it is a failed fan relay?

If so, is the relay easy to locate and/or replace? Sorry, but I am completely ignorant about this stuff.

[imeduc]

You dont say what furnace you have are how old. Can be fan -limit control or down on the board there.Could check power to the fan and see if its that just the one speed on the motor is doing this.

ED

My mistakes dont define me they inform me.

[jaristotle]

Thanks ed, it's actually working fine now.

[JohnnyEnglish]

What was the fix? I suspect the relay...

[HayZee518]

Could be the start winding in the motor. There is a centrifugal switch inside the motor which disconnects the capacitor when the motor is up to speed. Repeated starts could trip a thermal overload in the circuit. When's the last time you lubricated the motor? You say it works fine now, that's odd. seemed to fix itself - not hardly - look into the motor or bearings.

[Hube]

Hayzee; It cant be the winding, as it starts ok in "on" and in cool mode.
most likely the fan relay /control.

[jaristotle]

yes it was the relay

[Hube]

Glad its working..... Thanks