Furnace lights but no fan

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Soapm

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Our Church has two Lennox G9 furnaces. One of them works fine but the other, I can see the burner light but the fan never turns on. Then, after a while the burner goes back out, then minutes later it lights again but no fan.

Anyway I can troubleshoot this? It's below zero and all the furnace people I call are backed up and can't get to us anytime soon. We have a watch night service tomorrow and I'm hoping we don't have to cancel it due to insufficient heat.
 

Cacher_Chick

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First check is to see if the blower will turn. If that looks OK, test to see if the control board is providing power to the motor. It is not uncommon for a blower motor or start capacitor to fail.
 

Soapm

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I don't know how to make the fan turn on and there are only two wires to the thermostat so no way to turn it on from there. I am sure it's just jumping a terminal to put AC to the motor but I have no idea how to proceed.

Thanks for the response...
 

Jadnashua

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First, turn off the power, then get a short piece of wire and at the furnace, install a jumper between the R and the W terminals...that effectively, is what would happen if you had a manual/auto fan switch on your thermostat. Then, turn the power back on. If the fan turns (it probably won't), it is probably the fan limit control switch which senses when the air is hot enough, then turns the fan on, and shuts it off when it cools back down. If the fan does not turn on, it's likely the fan relay, but could also be the fan motor itself.

Proceed with caution...if you're not comfortable about doing this, do not. The contacts should only have 24vac (or around that) on them, but playing with electricity can get you hurt. Best left to someone trained on it.
 

Soapm

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Thanks for all the help, a furnace guy came by today and one of the wires to the blower motor had broke off. He put a terminal on it, plugged the wire back on and charged us $240. Not bad for the 20 minutes he was here.

But I'm a happy camper at this point.
 
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