Fan motor in Trane air handler not coming on. Capacitor?

vacman · February 18, 2023, 02:33:25 PM

HI.

The fan motor in my Trane air handler is not coming on. Even if I start it spinning by hand. Does this mean it's not the capacitor?

By the way, the motor spins very quietly, and spins for about a whole minute with a manual spin. Could the motor still be bad?

The unit is from 1986, but has been flawless all this time. I keep it clean.

Thanks

Admin · February 18, 2023, 02:57:37 PM

There's a chance it's the control board not sending power. If you disconnect the fan wire form the board and wire it to the continuous power coming to the furnace and it runs it may be a bad board relay. If it doesn't run it could be a capacitor or fan motor.

vacman · February 19, 2023, 02:46:11 PM

Thanks, admin. I'm not confident working with the wiring, but I do want to test the capacitor. Can I test the capacitor while it is still hooked up and power off? I would discharge it with a screw driver across the 2 terminals first. Hope that does not damage anything.

Then I would hook up the 2 probes from my multimeter and look at the microFarads reading.

The cap is only 10 micro Farads and 370 VAC. Would it be damaged by using a screwdriver to discharge it? I was ready to do so, then came across posts saying that it was harmful to the capacitor, and one should use a cap discharge tool instead.

vacman · February 22, 2023, 03:11:55 PM

I removed and tested the old cap. It was bad. Only 5 microfarads, supposed to be 10. I installed a new cap, and the fan still does not come on.

I want to rule out the outdoor unit. It works great. Compressor comes on, outdoor fan comes on. Do I need to check the capacitors on the outdoor unit also? Do any of the outdoor capacitors affect the air handler blower ?

Just ruling out the outdoor unit would be a load off my mind.

Porcupinepuffer · February 22, 2023, 05:56:32 PM

Post your model and serial of both units. Your outdoor unit almost certainly has no bearing on the problems with your indoor blower. Show the specs of the blower motor also.

Admin · February 22, 2023, 06:07:28 PM

At this point it's likely a bad fan motor or control board, in the air handler. Use your multimeter to verify the board sends 120V to the motor. There may be multiple speeds so make sure to test each terminal that each fan speed wire connects to on the board. If it's sending 120V then it should be easy to find a universal fan motor. Make sure to replace the capacitor if the new motor rating is different. A run capacitor doesn't start the motor it just boots the current so if it was faulty, it may have caused the windings in the fan motor to fail.

Sometimes you can switch to a different fan speed and the motor will work, but it should still be replaced.

vacman · February 23, 2023, 04:23:45 PM

Thanks for the replies.

I am leery of harming my electronics by moving wires, etc, so I want to make things as simple as possible for myself. I do a lot of automotive mechanical work, but this hvac electronic stuff is new for me.

I read somewhere that I can short the G connection to the R connection on the front of my control box, and that would start the fan motor, if indeed the motor is still good. Would this be a harmless way to test the motor?

And could I use my multimeter to test voltage between G and R ? Should be 24 volts, right ? Or zero ?

Thanks

vacman · February 23, 2023, 04:27:46 PM

Quote from: Porcupinepuffer on February 22, 2023, 05:56:32 PMPost your model and serial of both units. Your outdoor unit almost certainly has no bearing on the problems with your indoor blower. Show the specs of the blower motor also.

The air handler model number is BWV724A100E0. And it is a Trane. from 1986. I can get the serial number for you too, if it would help. Thanks. will look for blower motor specs. I know it is 1/4 horsepower.

Would using the system in cooling mode to see if the fan came on, be of any help?

I have already tried just moving the switch on the thermostat to 'fan' and all that does is make the control box hum. Fan stays off.

Admin · February 23, 2023, 04:40:23 PM

Jumpering R and G is the same as turning your thermostat fan from auto to on. I'm not sure if your continuous fan speed is the same fan speed as your heating or cooling. It's worth a try. If the continuous fan speed is low speed, then it likely would not supply enough airflow for the heating or cooling.

And it's possible only one relay on the board failed which feeds whatever speed you're trying to run so really without a multimeter you can't troubleshoot if it's the fan motor or the board.

vacman · February 23, 2023, 05:07:22 PM

Quote from: Admin on February 23, 2023, 04:40:23 PMJumpering R and G is the same as turning your thermostat fan from auto to on. I'm not sure if your continuous fan speed is the same fan speed as your heating or cooling. It's worth a try. If the continuous fan speed is low speed, then it likely would not supply enough airflow for the heating or cooling.

And it's possible only one relay on the board failed which feeds whatever speed you're trying to run so really without a multimeter you can't troubleshoot if it's the fan motor or the board.

I have a multimeter.

I am sure my system has only one fan speed. But are you saying there is a 'continuous' fan speed that might be different from the regular fan speed? And that jumpering R and G on the front of the control box would possibly get the fan to run at this 'continuous' fan speed ?

Even if it comes on at a speed that is too low, at least we will know that the motor works. I am viscerally reluctant to short anything out, but willing to try it, as long as it is safe for the equipment.

vacman · March 01, 2023, 05:42:50 PM

Quote from: Admin on February 18, 2023, 02:57:37 PMThere's a chance it's the control board not sending power. If you disconnect the fan wire form the board and wire it to the continuous power coming to the furnace and it runs it may be a bad board relay. If it doesn't run it could be a capacitor or fan motor.

I'm not confident enough to move wires, but I was able to do some testing with a multimeter. I was able to get the wires off the fan motor.

I could not get any voltage at those wires during any of my tests.

I did get 28 volts between R and G on the control box, when the fan was not called for, and zero volts between R and G when the fan was called for (thermostat set to 'fan'), which is as it should be, I believe.

But always zero voltage at the wires for the motor.

Does that imply a bad board?

If I jumper G and R on control box, with thermoset set to 'fan', will that bypass the board and send power to the fan motor?

And is it OK to jumper R and G live? As in connect a wire or paperclip (with gloves on) between R and G with power already on?

Admin · March 01, 2023, 07:56:12 PM

It's always safer to turn the power off an install a jumper wire between R and G but you could do it live.

I would disconnect the neutral and fan motor wire directly off the board and wire them into the line voltage and neutral wires feeding the air handler with the power off of course. Then, if you turn on the power and the fan motor starts, you know it's a bad board. But at least this way the system will work however, the fan will run 24/7.

vacman · March 02, 2023, 04:14:41 PM

Quote from: Admin on March 01, 2023, 07:56:12 PMIt's always safer to turn the power off an install a jumper wire between R and G but you could do it live.

I would disconnect the neutral and fan motor wire directly off the board and wire them into the line voltage and neutral wires feeding the air handler with the power off of course. Then, if you turn on the power and the fan motor starts, you know it's a bad board. But at least this way the system will work however, the fan will run 24/7.

Thanks. Do you mean it is safer for the person to do it that way? Would the system care if I shorted it live?

vacman · March 03, 2023, 11:12:05 AM

I got a connector apart, and got good contact to the wires there, and tested for voltage to the blower motor.

I got 21 (twenty one) volts in both fan on, and fan off mode.

Was expecting 120 volts in fan mode, and zero volts in non fan mode.

Why would the voltage ever be 21 ? Is that the default voltage when fan is not called for ?

vacman · March 07, 2023, 02:04:18 PM

I jumpered between G and R and got a click from the control box when I put the jumper on, and another click when I took it off. Is this the relay inside the coming on and going off ? I guess that means the relay is working.

chillerelvis · March 08, 2023, 09:13:54 AM

If not even a humming sound would suspect no power getting to motor. Does it ohm out?

vacman · March 08, 2023, 11:05:21 AM

Quote from: chillerelvis on March 08, 2023, 09:13:54 AMIf not even a humming sound would suspect no power getting to motor. Does it ohm out?

I haven't tested it yet for ohms.

But I did get a reading of 120 volts on one wire that feeds into the motor. It was upstream at a connector I took apart, that had two wires on the upstream side and three wires on the downstream side. One wire had zero volts and the other one had 120. With thermostat set on 'fan' position. So that seems to indicate I am getting 120 near the motor. It just has to go through the connector to the motor.

I grounded the black probe of the multimeter on the cage for the testing. Previously I had been testing for voltage by putting red probe in red wire and black probe in black wire, and got 21 volts, which no one can explain.

Porcupinepuffer · March 08, 2023, 05:04:21 PM

It sounds like jumping the R and G is forcing the relay coil to try and do its job, but you don't have proof of this if you don't check to then see if you get 120v on the terminal leaving the control board that the relay is closing. Contacts could still be bad inside the relay.
Since you have found some wires or two that have 120v going to the blower, try checking which ones get and don't get 120v when you jumper R and and G. There should be a wire to the motor that goes to 120 when you hear that click and then loses it when you no longer have it click.

The 21 volts is probably just phantom voltage where your meter is just picking up a magnetic field through the circuit. A lot of times those phantom voltages contain next to hardly any amperage. The meter requires no load to read voltages, but if you were to try connecting a small load that would run on 20 volts, it would probably not work at all and immediately drain that voltage to nothing.

vacman · March 09, 2023, 03:34:05 PM

Quote from: Porcupinepuffer on March 08, 2023, 05:04:21 PMIt sounds like jumping the R and G is forcing the relay coil to try and do its job, but you don't have proof of this if you don't check to then see if you get 120v on the terminal leaving the control board that the relay is closing. Contacts could still be bad inside the relay.
Since you have found some wires or two that have 120v going to the blower, try checking which ones get and don't get 120v when you jumper R and and G. There should be a wire to the motor that goes to 120 when you hear that click and then loses it when you no longer have it click.

The 21 volts is probably just phantom voltage where your meter is just picking up a magnetic field through the circuit. A lot of times those phantom voltages contain next to hardly any amperage. The meter requires no load to read voltages, but if you were to try connecting a small load that would run on 20 volts, it would probably not work at all and immediately drain that voltage to nothing.

Thank you for the explanation of phantom voltage.

I will see what happens with the 120 volts and the clicks when jumpering R and G with 'fan on'. Or should it be 'fan off' ? I could test in both conditions, actually.

vacman · March 14, 2023, 03:29:37 PM

DId some more testing of voltage between R and G in various conditions.

Did some more testing. I took apart the connector in the image that is under the yellow caution sticker. There were just two wires on the left connector, and three wires on the right connector.

I tested the two wires at the left connector, by grounding the black probe of the multimeter, and inserting the red probe into the appropriate wires of the left connector. I tested in fan off and fan on, not jumpered. I then tested in fan on, fan off, jumpered (between G and R).

One wire was red, one was black. In every case, I got 120 volts at the black wire, and zero volts at the red wire. So fan on, fan off, jumpered, not jumpered results in zero volts at the red wire.

I could still get a click on and a click off, when jumpering between G and R in 'fan off' mode, but the multimeter never moved off zero for the red wire.

Hvacpimp · March 14, 2023, 04:48:54 PM

I'm with the admin on this one, I think the board/relay is bad. If your not comfortable with the wires hire a tech

vacman · March 15, 2023, 01:48:18 PM

Here is the fan relay, inside the control box. Could I remove two of these wires, and connect them, to see if fan comes on? Hard to see, but the wires are in the rightmost 3 slots on the top, and in the rightmost three slots on the bottom. No wires in the middle row. 6 wires total on the front of the relay. Has an additional black wire going along the top, to the rear of the relay. relay 1.JPG

vacman · March 27, 2023, 09:44:55 AM

Update : I got it working. One day I had 120 volts at the motor wires and the capacitor, so I hooked all the wires up, and turned it on and the darn thing is working again. Yes, the fan comes on and blows strong.

Not sure what fixed it. Maybe I moved the right wire and gave it a better connection. Really don't know. I have a nice record of what wires I touched, etc.

Thanks for your help !