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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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Hello, I have a Lennox furnace which was installed in 1997

Customer Question

Hello, I have a Lennox furnace which was installed in 1997 with air conditioning. Automataic fan switch not working. Furnace works if I turn the thermostat up and set the switch for manual. Although, once it reaches set temperature, I have to turn off the fan switch or else it will keep running. Can you tell me what the problem might be?
Submitted: 6 years ago.
Category: HVAC
Expert:  Heath replied 6 years ago.

Heath :

Hello my name is XXXXX XXXXX will be my pleasure to assist you. The problem is the fan limit in the furnace . If the thermostat is set to manual it will come on because the power is sent directly to the blower motor. It won't come on for heat because the power has to go through the heat sensor in order for the blower to come on it has to reach a certain temperature before kicking on the blower.

Customer :

Furnace goes on but blower doesn't unles I put the fan swithc on manual.

Expert:  Tim H. replied 6 years ago.
Thanks for giving me the opportunity to help! The Lennox G23 furnace has a circuit board that times the blower on in the heat mode. I'm assuming you are having problems in the heating mode. Two things may be possible: 1) the board is bad, or 2) your low speed blower is not working. In other words the lead for low speed blower is not starting the blower due to windings internally being burned out. I've seen both situations happen. You'd have to do some voltage checks to confirm which one of these was the case.