Gas and Oil Home Heating Furnaces - Blower Repair

Good morning. The blower in our Lennox HVAC will not come on when the Fan switch is placed in the "on" position. The circuit board shows two flashing LED's which indicate "normal" operation. Any ideas. Thanks
:confused:

I would suggest checking the connection from the thermostat to the furnace. If the fan works during normal heating but not on the fan only setting, it is possible that the signal from the thermostat to the "fan on" control wire is not getting to the furnace. In most thermostats a separate control wire is used to activate the heating (which includes the fan) and the fan only mode.

Is this the tstat that was put in with the furnace.Did the blower work on fan on them?? You can jump R to G and see if the fan will come on just to see if the fan relay is working;) ED

Originally posted by rav12
I would suggest checking the connection from the thermostat to the furnace. If the fan works during normal heating but not on the fan only setting, it is possible that the signal from the thermostat to the "fan on" control wire is not getting to the furnace. In most thermostats a separate control wire is used to activate the heating (which includes the fan) and the fan only mode.

Thanks for the reply. I checked the Thermostat wiring and all appeared OK. The fan is not working with the fan switch in either the auto or fan on positions. The cooling system does operate. I'll check the fan circuitry in the unit itself. Thanks for the tip.

a/c works.....does fan come on? if not i am thinking motor...does it hum or try to start, smell burnt? able to spin off?

You are correct, the a/c works but the blower does not. Turned the system on auto a/c and auto heat. Re: a/c, the outside compressor and refrigerant loop worked fine until it froze up. This is not a surprise if the blower is inoperative. The heat cycled on, but cycled off when the blower did not operate. For both the a/c and heat, once the system cycled off, I could hear what sounded like the blower motor rotating inside the housing. This is consistent with the circuit board flashing that is operating normally. Believe the blower is receiving a signal from the circuit board and is turning slowly, but not hitting on all cylinders. Coming to the conclusion that the motor may be shot. Any further thoughts on how to check if the motor is the problem?

Have you opened up to check if something has not got into the blower and jammed it up.

Assuming it is not the case you can use a multimeter to see if the blower is being supplied the correct voltage. If this is not something on the control board may be the fault. If voltage is present use the resistace setting on the multimeter and measure the resistance across the motor connections - it should be low. If it is high - in the KOhms or Mohms the the coil could be open.

The coils could also be shorted - not easy to troubleshoot this with home eqipument. You will need an oscilloscope and a signal generator to test for this condition which most peole don't have.

turning slowly......can you spin it off? may be capacitor, if not motor.

Sounds like the motor capacitor. I had the same problem with my forced air furnace about 15 yrs ago. Replaced the capacitor and it's run fine ever since.

Like hvac4u said with it calling for the fan to run look out now . But give the fan a push and see if it runs. If it does get a new capacitor for it the same kind. If it dont run get a new motor.;) ED