Trane 4 Spd blower motor cutting on and off

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Old 08-14-13, 05:22 PM
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Trane 4 Spd blower motor cutting on and off

Hi,

Thank you for offering this forum.

I have a Trane TUX100C948B3 Furnace. The blower motor continuously will shut off on its own after running for only about 1 min. I jumped the LV side of the board as to bypass the thermostat, but blower motor shuts off on its own. The motor itself feels very hot to the touch. I pulled the housing out of furnace out and the motor spins freely. I did have to move the squirrel cage back toward the motor. It might have been rubbing on the housing. Am I correct in assuming the motor is overheating and shutting itself off until it cools down enough to restart? I did check the capacitor, without the leads, it had the correct MFD. Could there be a problem with the control board not calling for blower? and which leads off (circulator blower) hot side of the control board supplies power to blower motor and how is the speed of the blower motor controlled?

Sorry for the long list of questions

Thank you in advance,
Scott
 
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Old 08-14-13, 07:05 PM
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Welcome to the forums.

Does the motor run for a minute at normal speed and then shut off or does it sort of limp along ?

The colors on the motor select the speed.
White = neutral
Black = high - usually the tap used for A/C.
Blue = medium high - usually used for heat.
Yellow = medium low - could be used for heat but is normally parked (not used)
Red = low - rarely used and is most likely parked (not used)

So if you turn the A/C on or put the thermostat in FAN ON mode you should measure 120vac on white and black wires.
 
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Old 08-15-13, 04:39 PM
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The motor runs at a decent speed. I can feel the airflow from a few of the registers ( I didn't check them all). But the vapor lines end up super cooling so I usually dont' let the system run too long. Would it help if I turned off the condenser unit and see how often the blower motor cycles on and off? I am planning on hooking all the wiring back to normal (then turn just Fan to on) and will see if the Cool terminal sends out 120v. And yes two of the terminals are labeled "Park"

I also have a Honeywell "Perfect Climate Comfort Center Control System" that could be affecting the call for just Fan. The thermostat model number PC8900 and W8900 remote module. I have a total of 3 of the same systems in the house, but after switching Tstat same results. Its tempting to buy a standard tstat and run new wiring to furnace to eliminate tstat issues.
 
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Old 08-15-13, 05:10 PM
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Everything put back together and just called for Fan from tstat. 120v going into control panel in furnace, but only 98 at the Cool terminal. I assume that is not normal?
 
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Old 08-15-13, 05:15 PM
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No.....98 volts is not normal.

Check again from black to ground this time. This will confirm that the neutral is ok.

If it turns out that you still have 98v from black to ground try this:

Check from all non parked wires to neutral (white). See if any are over 98v.
 
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Old 08-15-13, 06:25 PM
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Sorry forgot to mention I checked both ground and neutral. Just checked all of them again and get same reading with ground or neural.

Black (cool) = 98.5v
Blue (heat) = 120v
Red (park) = 150v
Yellow (park) = 135v

Thank you for your help.
 
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Old 08-15-13, 06:31 PM
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I'm going to have to look up your manual. I was under the impression it was a 120v motor but it appears it may be a 240v one.

Your voltages don't really make any sense.

The parked wires should be the low ones. The actual powered wire should be the highest voltage. Are you setting your meter to AC volts ?
 
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Old 08-15-13, 06:52 PM
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I assumed I had the meter set correctly. I will check again. The motor is a 115v GE 3/4hp 4 speed 1100rpm 10.5 amp model no. 5kcp39sgp964as
 
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Old 08-15-13, 07:04 PM
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Didn't make sense to me either. I unplugged both parked leads to motor and no voltage at the terminals. Then un plugged the Cool lead and motor actually increased speed. There was no voltage on the cool terminal. So the fan was running with only heat terminal plugged in and that voltage was 120v. but after about 4 min of running it shut itself off. Voltage was still present and I could smell the motor burning and it was extremely hot to touch.

Can I test the different leads going to the motor for resistance? should any of them be open?
 
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Old 08-16-13, 08:02 AM
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The parked terminals are just blank holders.

Your furnace uses an IFC (integrated furnace control) to control blower functions. It appears that it may have a problem. It should not allow the heat terminal to be energized when in cool or fan on mode. It actually sounds like your module is stuck in heat mode. Energizing two fan leads at once will make the motor run hot. You will need to try heat and see whats energized and then try cool.



On page 11 in the following link is the schematic I've been using.
Trane Commercial Uploads - PDF manual
 
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Old 08-16-13, 10:33 AM
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I unplugged all the terminals except Cool. Tsat set to AC and the fan still cycles on and off every minute or so. 120v is still being supplied at the Cool terminal and the motor is hot and doesn't smell good. should I try clamping my amp meter and watch the draw on the hot side feeding the motor? Do you know what would be a range of amps it would draw to shut itself off internally?

The control module must call for the heat terminal to supply power to the blower motor when tsat called for Fan only. Sorry if I didn't give enough detail. When I had power at the Heat terminal (tsat calling for fan only) there was no voltage at the Cool terminal and vice versa when the tstat called for AC Line voltage was at Cool but nothing at the heat terminal.

I am leaning toward a Blower motor
 
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Old 08-16-13, 02:31 PM
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LMK if these readings are normal?

Set tstat to heat and everything turned on like it was supposed to and blower mower stayed running for 4 min at 14 amps before I turned it off. Then tried tstat for AC. Blower motor start amp draw was 22 then run draw was 18 for a min before cutting off on its own.

So I switched the Blue (Heat lead to motor) to the cool side of control board. Set tstat to AC and Fan worked for about 5 -10 min at 14amp draw before shutting itself off. When I unplugged the blue wire, the motor had a surface temp reading of 200 degrees F and smelled like it was burning.

I don't know enough about motors , amp draws and internal safety shut offs to do anything else.
 
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Old 08-16-13, 06:58 PM
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When you tried it on heat.....did it come right up to speed ? If yes then the motor is bad. If it took a while to come up to speed then I would suspect the starting capacitor.

Pretty sure at this point that it's the motor.
 
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Old 08-16-13, 07:19 PM
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Yes it came right up to speed. and ran at a constant speed until it shut off.

Thanks for your help. I will hit the supply houses in the morning to see if I can find one.

I have 40 retail spaces I take care of and the one at my house gives me trouble.

Thank you PJmax. Have a great weekend.

I will post an update when I replace blower motor.
 
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Old 08-16-13, 10:32 PM
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When you pick up motor make sure to pick up a new capacitor for it. The new motor should specify the size.
 
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Old 08-17-13, 05:56 AM
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If the motor is rated at 10.5 Amps and your pulling 18 and 14 amps, then the motor has a shorted out winding which is causing the thermal shut down.
 
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Old 08-19-13, 11:33 AM
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New blower motor and cap. Everything is working fine. Thanks for your help.
 
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Old 08-19-13, 05:29 PM
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Thanks for stopping back..... well done
 
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