My furnace is working but the blower motor won't turn off. I can disconnect all of the wires on the thermostat and the motor still runs. The only way I can stop the motor is to either take the face plate off which disengages the switch or to unplug the power cord. I just put a new motor on the furnace and I think my last one burned up because it would not shut off. My furnace is an older one. I heard it could be the relay or the transformer. Is there a test I can do? Please help!!

Well you can begin by letting us know our experience level. For example most motors are either capacitor start or induction. Capacitor start motors will have a capacitor mounted on the motor. Induction motor usually have a clutch and pawl assembly that kicks in when the motor's revolutions are correct.

Transformers rarely run motors, at least in my limited experience.

Now, exactly how is the motor being told to shut off. Is the motor controlled by a circuit board? Why are you saying that the blower motor is constantly on? If your blower motor is plugged into an outlet, how much amperage is it supposed to draw. Blower motors and their wheels are pretty decent sized assemblies, are you supplying the proper amount of power and amperage to the motor?

If I had to start troubleshooting this, I would star at the motor and work towards the circuit board. To do his you need to have a schematic and a component placement map.

If you have them and know how to use them, determine what is needed to shut the motor off and then see if there is a obvious failing component in the circuit path.

If you don't have them, please have the good sense to call a qualified heating and cooling technician before you touch anything.

Well you can begin by letting us know our experience level. For example most motors are either capacitor start or induction. Capacitor start motors will have a capacitor mounted on the motor. Induction motor usually have a clutch and pawl assembly that kicks in when the motor's revolutions are correct.

Transformers rarely run motors, at least in my limited experience.

Now, exactly how is the motor being told to shut off. Is the motor controlled by a circuit board? Why are you saying that the blower motor is constantly on? If your blower motor is plugged into an outlet, how much amperage is it supposed to draw. Blower motors and their wheels are pretty decent sized assemblies, are you supplying the proper amount of power and amperage to the motor?

If I had to start troubleshooting this, I would star at the motor and work towards the circuit board. To do his you need to have a schematic and a component placement map.

If you have them and know how to use them, determine what is needed to shut the motor off and then see if there is a obvious failing component in the circuit path.

If you don't have them, please have the good sense to call a qualified heating and cooling technician before you touch anything.

First off, kindly post the make and model number of your furnace for us at this site, so we may be beter able to assist you... some of us... such as myself, have a reference library of many brands of install and technical manuals that I use daily in my job... thanks.

The older furnaces aren't that complicated to work on. Usually the problem is a bad relay. Unplug it, pull the panel off and look around inside. Follow the wires from the blower motor back to a box. If it just has 3 wires beside the one to the blower it should be the relay, plug the furnace back in. Give the box a good knock with your knuckles or a screwdriver handle. If the blower stops, you have found the problem. Unplug the furnace. Note haw the wires are connected, and remove it. I don't think the DIY friendly big box stores have them. You may need to go to an electrical or HVAC supply. They may match it, or want the model number of the furnace to look it up.

Knocking on it does always stop a stuck relay. Next step is to unplug it again, and remove one of the smaller wires. If the blower starts up when you plug it in, again, the relay is bad. If not follow the small wires. One should go to the transformer, and the other into the furnace. It will connect to a limit switch. Again, remove it, and go buy a new one.

Some furnaces will have the relay, transformer, and limit switch all built into a fan control. If so, you may have to replace the whole thing. The newer ones have the relay on a circuit board that costs an arm and a leg to replace. You can go to the sticky at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html

A schematic and a few tools and knowing how to use them helps. Often, the furnace will have a schematic on it. Not all problems are easy to find. You may still have to post back brand, model, etc. so somebody can tell you exactly what for look for.