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How to replace a blower motor on a forced air furnace.


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How to replace a furnace blower motor

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This page will help you replace your blower motor on your forced air furnace.
The first thing you need to know is, this can be dangerous, you can be injured, you can loose your fingers, you can be electrocuted, you can be burned and you can be killed,
you can also burn your house down,
Master Plumber USA, and Thomas P. Reardon can not be held reasonable for anything that may happen
as a result of you following the instructions on this and any other page on this website,
You assume full responsibility for what you do.
It is always best to have a professional do this kind of work for you.
Now make sure the power to the furnace is off, just because it is not running, does not mean the power is off, just turning the thermostat down does not mean the power is off,
Make sure the power is off at the circuit breaker, or the fuse is removed.
I have found that 90 percent of the time circuit breakers and fuses are marked wrong in the panel box, use a meter and make sure the power is off.

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This is an old Lennox furnace with a spark ignition that is built in to the gas valve.
I can not give any instructions on how to troubleshoot this gas valve.
If you have a furnace like this and need help with the gas valve of ignition, call a professional.
The motor on this furnace burned out, it is not always apparent why a motor burns out, but in this case it is a safe bet it burned out because of neglect. People seem to be under the impression, a gas fired furnace never needs to be cleaned or serviced, this is a big mistake that can cause a very dangerous situation. All furnaces gas or oil need to be inspected and serviced every year This is the blower motor compartment. In this furnace the filter is located in the blower motor compartment. The blue thing shaped like a U is the filter. you may notice how dirty it is. A filter needs to be cleaned or replaced every month, not cleaning or replacing the filter as often as you should, shortens the life of the furnace, the controls and the blower motor, not to mention it cuts down your efficiency.
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This is just a close up of the gas valve. behind the gas valve is the cam stat. The cam stat controls when the furnace fires, stops firing and turns the blower on and off. OK, now it is time to cut some wires, Are you sure the power is off, and no one in the house will turn it back on? This furnace has a 3 speed motor, others have only a single speed motor, some have a 3 speed motor but only use one of the speeds. You want to cut the wires going to the motor, cut close to the motor, so that you have as much wire left going back to the control as possible. make sure you are only cutting wires that go into the blower motor, many blower motor compartments have a high limit switch. you do not want to cut the wires. The whole squirrel cage housing needs to be removed, on most furnaces there are 2 bolts one on either side that need to be removed. Some are on the bottom others are on the top, this one is mounted to the top. Care needs to be taken not to have the whole thing just drop.
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Unfortunately this electrical box is in my way, and will have to be removed in order to get the squirrel cage housing out, please see the following pictures. Note the screws need to be removed from the top I have a flexible drill bit extension with a magnetic nut driver on it, it makes getting at the screw heads allot easer. Now with the box hanging I can pull the squirrel cage housing out and just push the loose wire box out of the way. You do not need to remove the box and all the wires.
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Once I got it out and set it on the floor, it this very small room, I can see just how dirty this furnace really is by looking at the following pictures you will see what happens when you don't have your furnace inspected and serviced every year. You may find it hard to believe, but I have seen worse. The blower motor could not breath and was over heating on a regular basses. And then in the middle of the night, in the middle of a cold snap, in Anchorage Alaska this blower motor quit. If these people were not home at the time, there whole house would have froze, all there pipes would have broken and even there toilets would have cracked and would have needed to be replaced, believe me I have seen it happen. All for the cost of a filter. To remove the motor from the squirrel cage, first remove the ground wire, then remove the 3 bolts that hold the mounting bracket to the squirrel cage housing. then turn the whole thing over.
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On the side, where the motors shaft comes through the squirrel cage, there is a 1/4 square nut. loosen this nut as far as you need to, allowing the shaft to move. Sometimes even with the nut removed the motor shaft will not move, if this happens use some king of liquid wrench. If you have to tap it out, be careful not to mushroom the shaft end, because then you will never get it out. Now flip it over again and you have the old motor out. Make notes where the motor brackets are located on the old motor before you remove them. Most new motors do not come with new brackets, you will need to use the old ones. there are many different types of brackets. if your new motor has oil ports you want to be sure they will be facing up when the blower motor is back in place. Now you will need to put the bracket on to the new motor. It's important that you replace the motor with the correct size motor, you can use the old motor as a guide or you should be able to get the information from the plate inside the furnace. because we do so many motors and there are so many different brands, we use a universal, motor. We still have to use the right size in horse power and the shaft has to be the same size, but the motors we use can be used for either clockwise or counter clockwise operation.
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This is the box this one came out of. note the brand name and horse power and it also tell us the right capacitor to use. replacing the motor with out replacing the capacitor is foolish make sure to replace the capacitor when you replace the motor. The label attached to the new motor tells you, what wire is what, this is very important, because the wires may not be the same colors as the motor you replaced. Make sure the bracket is on the motor correctly and that the bracket will not interfere with the wires and that the wires will reach the ends you cut off before. In the images below you will see the wrong way for the squirrel cage to be positioned. to far to either side will rub and make a lot of noise and cause damage to the squirrel cage and housing. make sure it is centered and spins freely.


By Thomas Petito Reardon
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