furnace blows cold air on summer, but does not blow on winter

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mystique 17 years ago

My furnace keeps lighting the burners while the blower switch is on winter, but the blower never turns on. When I switch the blower to summer, the blower turns on and stays on, but the burners never ignite; so the furnace just blows cold air into the room. I've been reading about thermocouples, but it seems that is not the problem, because the burners actually kick on, just not the blower. The switch doesn't seem defective, because it has different settings when I switch it from summer to winter to off. I know the blower works, because it blows constantly when I put it on summer. I know the burners work because they are almost constantly on when the blower is on winter. It seems to me that I have all the parts of a working furnace, they just don't know how to play nice ; - (

Concerning the thermostat: I had the same problems with the thermostat connected, but I took the wires out and twisted them together to try to get the thing to work this morning.

Any help at all would be greatly appreciated

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Bob F 17 years ago

There is probably a switch that senses the temp in the heat exchanger and turns on the blower as it warm up. You need to check that switch. It may have temp adjustments for the on and off temp.

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Edwin Pawlowski 17 years ago

No, you still have one part not working. That is the thermostat that senses the heat and turns the blower on. If you have no idea about it, call a service tech. Tell them the problem and they may bring the part with them. Simple fix.

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N8N 17 years ago

or it could be a flame sensor, depending on model.

nate

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DerbyDad03 17 years ago

re: That is the thermostat that senses the heat and turns the blower on.

Are you saying that the thermostat in my living room monitors the heat exchanger temperature and turns on/off the blower?

I'm not sure how it works with a "modern" furnace, but I can say without a doubt that my old furnace had a sensor in the plenum that controlled the blower based on the air temp. You needed the thermostat to call for heat to turn the burners on, but you also needed heat to turn the blower on.

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crumbbuma 17 years ago

It's inside the furnace.

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Edwin Pawlowski 17 years ago

re: That is the thermostat that senses the heat and turns the blower on.

Are you saying that the thermostat in my living room monitors the heat exchanger temperature and turns on/off the blower?

No

I'm not sure how it works with a "modern" furnace, but I can say without a doubt that my old furnace had a sensor in the plenum that controlled the blower based on the air temp. You needed the thermostat to call for heat to turn the burners on, but you also needed heat to turn the blower on.

Yes, that is the one. There is a thermostatic controlled high/low limit switch that tells the blower to go on or go off. Depending on the model, there may be other controls too but I've not worked on a furnace in recent years and kept up with every control.

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The Daring Dufas 17 years ago

The fan limit control turns the fan on and off in furnace applications. Easy to test, easy to repair.

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TDD

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furnace blows cold air on summer, but does not blow on winter

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