Top 10 Reasons Why your Furnace Blower Motor is Not Working.
Here’s our blower motor housing, and inside, we have our blower motor.
1.) Bad Capacitor
The first reason is the capacitor could be bad. If you happen to have a Permanent Split Capacitor (PSC) blower motor, that has two brown wires attached to the capacitor.
If that capacitor is no longer any good then the Permanent Split Capacitor blower motor will not operate.
You could try to free spin it but the blower motor could overheat over time. You don’t want to do that and you want to make sure to go ahead replace the capacitor.
First, make sure the power is off to your furnace. Not just on your door switch, make sure the main power is off, you going to isolate your capacitor – take that off.
And you’re going to want to go ahead and short that out with something that’s bare metal.
By scrapping the bare metal across the terminals, we are discharging the capacitor to get an accurate reading with our Multimeter.
Take your Multimeter out and turn it on.
Press the select button until you get over to capacitance and you want to go ahead and hold your probes on the capacitor for about 10-20 seconds to get a good reading.
On our pic above, you see that we’re reading 7.63 microfarads and our reading on the capacitor was 7.5 microfarad. The capacitor is good but if it was bad, the multimeter is reading zero microfarads. We usually like to see them up or above the rating.
A bad capacitor also will look bulged sometimes, and if you see it leaking any fluid that’s also another sign of a bad capacitor. Especially, if you see it dripping down the side.
Also, make sure to replace capacitors with the same MFD/uF value as stated in the motor. If you take out a 440V AC capacitor, replace it with a 440. If you’re taking out a 370V AC then you can replace it with a 370 or a 440.
2. Bad Blower Motor Bearings
Another problem could be that the blower motor bearings could be bad. Make sure the powers off and then try to feel and see if it free spins.
And also see if there’s any rocking that occurs when you try to move it. That would both indicate that the bearings are bad if it doesn’t move or there are some rocking and binding up in there.
3. Thermal Overload
Another that could be the problem is the thermal overload.
This thermal overload is mounted right onto the electrical windings.
And if those electrical windings get hot due to maybe a bad capacitor or some other issue, over time this may take a long time to end up resetting.
If the thermal overload goes bad or the windings are overheating then replace the motor. Before replacing the motor also check to make sure there is no voltage drop when the motor is powered indicating a voltage problem.
So if you happen to have the blower motor that turns on every once in a while but then basically shut off on its own, it may be the thermal overload.
4. Blower motor has Shorted out inside
Another reason why the blower motor may not be turning on is possible that the blower motor has shorted out inside. If it pops a breaker any time, you turn the air handler on, these windings may have shorted together.
So basically, say your common wire has shorted with your hotwire or the hotwire is shorted to the ground frame and that’s why it’s popping the breaker. If it doesn’t pop the breaker and the blower motor is not turning on then the windings may have opened up so burnt apart but they’re not shorted against anything – indicated by a resistance reading of 0.L from a hot to common.
5. Bad Control Hub
You could have a bad control hub on the side of your motor.
If we were to test the windings, it’s a three-phase winding and it’s 4.5 DC voltage from the control hub to three-phase motor for DC voltage.
You can test and see 4.5 in there. You can check between each of these in the ground and have no resistance reading to ground.
Once you check this one, typically it’s not the actual motors itself but it is typically the hub or the module.
On the X13, you make sure that you have a 24-volt signal going to the motor and you have to look at the wiring diagram of the furnace or air handler to see which one of these is powered with 24-volts.
Make sure that you have your 120 volts into this or if it’s 240 for an outdoor package unit. Make sure it should have a line voltage all the time. Even if the blower motor is not called for electricity, any type of ECM blower motor typically always has your high voltage, and then it’s just waiting for either a 24-volt signal or a DCmillivolt reading with the ECM 3.0.
You can bypass the ECM 3.0 and the 2.3 with a tool called Technic Pro.
And you can just connect the tool or connect your 16 pin connector in and you can check your variable-speed motor operation with that.
6. Bad Control Board
The control board could be damaged and is not sending the communication to the blower motor.
In this case, the control board may not be sending the 120 volts or say 240 volts over to the PSE blower motor.
All of these the boxes in there are the relays and the relays maybe just stuck open or the winding may be bad in it or something could be bad that it’s not sending the 120-volt signal to the blower motor.
The control board should send the line voltage to the PSE blower motor anytime it has a 24 volt signal on the G terminal which can be read with a multimeter between G and C.
In the case of a control board sending voltage to a variable-speed blower motor, you check for 24 volts between the G terminal and the common to see if you have 24 volts. Then see if the blower motor is good. If the blower motor is turning on and it’s running properly then you know that your control board is bad.
You can test your blower motor with your TechMate Pro tool.
7. Dirty Air Filter/Damaged duct
Your blower motor is not able to push any air through the duct because of maybe a clogged air filter or possibly a collapsed duct or maybe even an open duct.
We’ve seen before in a crawlspace where the duct just down too low and it was touching the water. Eventually, rotted out and the airflow is just going right into the crawl space.
We’ve seen dirty filters damaging variables speed blower motors. It makes the blower motor apply more torque onto the motor and eventually, ends up burning itself.
We’ve also seen collapse ducts where animals get in or the duct is just too old it kind of falls apart in on itself.
8. Fan Limit Control
You may have this on an oil-fired or a gas-fired furnace. What happens is as the inside heat-exchanger warms up, it is supposed to turn.
What could be happening is the bi-metal could be jammed up onto the side and it’s just not allowing the wheel to move.
Sometimes this could end up being the culprit.
9. Bad Relays
If you’re equipped with some type of fan relay, to control the blower motor – try to notice if there’s a bad connection where it’s kind of burnt apart or possibly the coil inside is burnt apart.
It could be checked with just a simple resistance reading on the coil.
If you’re not reading well then that means that the coil is burnt apart so that would indicate that you have a bad relay.
10. Control Board is not getting Signal.
Your control board is not getting the 24-volt signal when you turn the fan on or if its in cooling mode.
Keep in mind that the thermostat does not send the fan signal in heating mode. The board, relay, or other control will allow voltage to the blower motor after ignition.
It may not be getting a 24-volt signal to the G wire so in this instance, turn the fan on and check from G terminal to C and check the reading.
On our pic, it shows 27.8 volts so that is good and that should be allowing the board to know that it needs to send voltage to the blower motor.
If you read point zero or if you’re not getting 24 volts or anything between 24 to 29 volts between G and common, then your thermostat is not sending the signal for the blower motor to turn on.
If you turn cooling on then your thermostat is going to send 24 volts to the G and the Y but with most Control boards, if you at least send 24 volts to the Y, it will then automatically send voltage itself to the G.
It will also turn the blower motor on and as the highest fan speed for the cooling mode. But if you have a relay system then your thermostat needs to send the 24 volts to Y and to G from the thermostat itself.
So, you just need to make sure that you have 24 volts going to the board to tell it to turn on, in this case, we can test the 120 volts coming off of the control board to our blower motor.
We’re going over to the heat terminal and the common for 120 volts. On the read, it’s 123.7 so when you’re calling for a G terminal, typically it powers the heat fan speed. Not the cooling fan speed but the heat fan speed typically.
So, those are the top 10 reasons we have on our list. Please note that these are scenarios that require you to know the basics of its parts. It’s still best you call your HVAC tech to see what’s wrong with your furnace.