Gas and Oil Home Heating Furnaces - Old Gas Furnance Fan Turn On
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ltlieu
12-21-06, 09:30 PM
My father is having trouble figuring out why the fan on the old gas furnance won't turn on.
He has poor english and I have no knowledge about mechanics, but this is all the information I can get; please excuse my lack of terminology:
The gas furnance is controlled by a thermostat located on an adjacent wall. When the thermostat is turned on (adjusting it to a temperature of around 70F), the furnance turns on and a blue flame appears, but the fan will not turn on. There is no motor noise or any movement.
My father tried different methods of figuring out the problem:
1) He removed the motor connected to the fan (has all sort of wires of different colors) by unscrewing four screws that held it in place. He checked the voltage (I assume) with a meter. To make sure that the readings are normal, he checked a similar motor from a working furnance and compared the two readings. We assumed that the motor was fine and was still puzzled why the fan wouldn't turn on.
2) He used the motor from the working furnance and used that motor to put back into the unworking furnance. But the fan still doesn't rotate.
3) He put all the original parts of the unworking furnance back. The motor is like plugged up to an outlet located right next to the motor. He unplugs the 3-prong cord. The then precedes to do some wiring work and connects an extension cord to the "raw" copper wires and connects the extension cord to a different outlet. We then turn on the furnance and the FAN ROTATES. We then assume that the motor to the fan works fine. But we didn't think about the outlet located right next to the furnance (inside).
So, I don't know what is wrong with it and neither does he. When the furnance is turned on (gas part works fine), we wait for a couple of minutes, but the fan DOESN'T TURN ON. He tells me that it is suppose to turn within less than a minute.
The gas furnance is very old, along with the other gas furnances located in the apartments. I would guess older than 20 years (considering I'm 19 years old and it's never been replaced while I was born). My dad tells me that the apartments have been there since WWII, but I doubt that the furnances are that old.
Thanks for any help that you can give.
He has poor english and I have no knowledge about mechanics, but this is all the information I can get; please excuse my lack of terminology:
The gas furnance is controlled by a thermostat located on an adjacent wall. When the thermostat is turned on (adjusting it to a temperature of around 70F), the furnance turns on and a blue flame appears, but the fan will not turn on. There is no motor noise or any movement.
My father tried different methods of figuring out the problem:
1) He removed the motor connected to the fan (has all sort of wires of different colors) by unscrewing four screws that held it in place. He checked the voltage (I assume) with a meter. To make sure that the readings are normal, he checked a similar motor from a working furnance and compared the two readings. We assumed that the motor was fine and was still puzzled why the fan wouldn't turn on.
2) He used the motor from the working furnance and used that motor to put back into the unworking furnance. But the fan still doesn't rotate.
3) He put all the original parts of the unworking furnance back. The motor is like plugged up to an outlet located right next to the motor. He unplugs the 3-prong cord. The then precedes to do some wiring work and connects an extension cord to the "raw" copper wires and connects the extension cord to a different outlet. We then turn on the furnance and the FAN ROTATES. We then assume that the motor to the fan works fine. But we didn't think about the outlet located right next to the furnance (inside).
So, I don't know what is wrong with it and neither does he. When the furnance is turned on (gas part works fine), we wait for a couple of minutes, but the fan DOESN'T TURN ON. He tells me that it is suppose to turn within less than a minute.
The gas furnance is very old, along with the other gas furnances located in the apartments. I would guess older than 20 years (considering I'm 19 years old and it's never been replaced while I was born). My dad tells me that the apartments have been there since WWII, but I doubt that the furnances are that old.
Thanks for any help that you can give.
KField
12-22-06, 05:31 PM
You guys didn't do too bad for your first foray into heating and electrical circuit troubleshooting. Somewhere between the incoming power and the outlet that the blower plugs into there is a temperature switch. It waits until the air is warm before turning on the blower. Otherwise cold air would be blown. The problem seems to be in that control. It may be a simple little black oval disc with two push-on terminals. It could be different that than but without some brand and model information I am at a dead end. Good luck and post back if needed.
Ken
Ken
nomore9to5
12-22-06, 05:35 PM
sounds like you have a bad fan relay. the furnace if it is over 20 years old probably has a fan/limit control mounted on it, contains a small round dial that turns as the temp rises in the furnace to send power to the fan. if that is not working properly then you will not get power to the fan motor. if this furnace has a circuit board however then it probably does not have this fan/limit control. trace the wiring diagram to see where the motor is getting its power from and with a meter check to see if the power is being relayed to it. if you give up you can always just wire the fan hot to run all the time by tapping into the main 115 feed into the furnace with the hot and common fan leads.