Lennox gas back ignites but blower doesn't come on. Replaced wall thermostat and blower came on briefly but did not satisfy set temp.

Do you have any way to check to see if you are getting power to the motor.

Unless you know that you do not know if the problem is with the motor or some other part of the furnace.

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Originally Posted by letmetellu

Do you have any way to check to see if you are getting power to the motor.

Unless you know that you do not know if the problem is with the motor or some other part of the furnace.

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Thanks for your help. Last night, I set the therm on 70 and had to turn fan to "ON" in order to have heat. As soon as the 70 temp was reached, of course the burner cut off but the fan continued to run, cool air. I've continued to "manually" keep the house warm by cutting the fan on and off. There has to be some type sensor that tells the blower when to come on when in automatic. Thanks again. Cold in South Carolina!

There are several way that a furnace uses to turn the fan on. It all depends on what brand and type of furnace you have .

Some use a time delay system, after your thermostat is turned on the relay waits for several seconds to turn on the motor to the blower, this can range from 60 seconds to 90 seconds.

Another way it a bi-metal switch. As the metal get hot it switches to make to contacts make contact and turn the motor on. There are other ways so it would help if I knew what furnace you had and maybe a model and serial number.

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Originally Posted by letmetellu

There are several way that a furnace uses to turn the fan on. It all depends on what brand and type of furnace you have .

Some use a time delay system, after your thermostat is turned on the relay waits for several seconds to turn on the motor to the blower, this can range from 60 seconds to 90 seconds.

Another way it a bi-metal switch. as the metal get hot it switches to make to contacts make contact and turn the motor on. There are other ways so it would help if I knew what furnace you had and maybe a model and serial number.

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LENNOX GAS PACK - 80,000 BTUH
Model #: GCS20R-411-100-4P
S/N : 5695B 03663
Has a date at bottom of label - 1992. Has this thing about seen it's better days? I had a rep (part time) come check it out Friday but said he couldn't find anything wrong with it. I've called several other companies and all are tied up right now. It's hard to find good, if any, H & C reps in this area. One suppose to be here later this afternoon. I'm trying to get a head start of repairing it myself if this person doesn't show or repair it.
So, I really appreciate you taking the time to help me.

Your service manual

http://www.hvacpartsshop.com/GCS20RX%20Series.pdf

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Originally Posted by hvac1000

Your service manual

http://www.hvacpartsshop.com/GCS20RX%20Series.pdf

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Thanks for the service manual. I tried to find one last night on line but couldn't find it. Helps to know what you're looking for! After looking through the manual, I can appreciate what you, the experts, do. Thanks again.

No problem.

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Originally Posted by hvac1000

No problem.

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Just wanted you to know that H & A rep came out today and found my Lennox Gas Pack problem. It was a burnt wire on the fan relay. He replaced the relay and I finally have heat. He first thought it was the fan switch (?) but before he put it on, found the relay problem.