Indoor unit fan "sounds" weak, air also weak

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Old 05-24-07, 11:56 PM
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Indoor unit fan "sounds" weak, air also weak

Need guidance.

I have a Lennox 12HPB heat pump unit running good for eight years. Only a few days ago, the indoor unit fan (in the attic) began to "sound" weak every time when it blows. There is cold air coming out from the vents but I can tell the air is weaker then normal. The fan will start but only blows for a little while and stops, never reaching the set temperature according to the thermostat. I went up to the attic and notice that the fan is blowing but sounds weaker than normal. The outdoor compressor fan seems blowing okay and strong. Need some guidance and advice where to start. Your help is much appreciated.
 
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Old 05-25-07, 05:31 AM
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How's the air filter ? Is the indoor coil clean ?
 
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Old 05-26-07, 08:52 AM
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Is the motor hot?

If your disconnect power after it stops, is the motor hot. Could be the capacitor is dead or dying and motor is stopping on overload.
 
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Old 05-29-07, 06:33 PM
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Did you mean the outdoor unit or the indoor unit regarding the motor and capacitor?

Additional information here may make my original problem description more clear:

I've checked the filter, condition is good. The return air duct definitely "sounds" and "feels" weaker than normal. The gas furnace unit in the attic (Lennox model 80UHG) also sounds and feels weak when it is running. Also, the outdoor fan will run continuously but the indoor fan only runs intermittently. When it does, it runs weak. Indoor temperature never reaches the thermostat setting. Also, when I switch the thermostat to continuous air instead of "auto" it doesn't start and run the fan as it should.
 
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Old 06-01-07, 02:21 PM
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Wink

when I switch the thermostat to continuous air instead of "auto" it doesn't start and run the fan as it should.
Check the board for fan relay here also check the Amp draw when the fan is on. If not up to par get new motor and capacitor for it
 
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Old 06-02-07, 11:41 AM
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Fan run capacitor tested good - what's next?

I removed the run capacitor from the fan motor and visually it is not swollen. The capacitor is rated 40 MFD x 370 VAC, I tested it using two different DMMs and they read 38.99 and 39.00 MFD respectively. I guess I should assume the capacitor isn't the culprit in this case but will have to check on the board itself? What about the thermostat?
 
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Old 06-02-07, 11:12 PM
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Also tested outdoor heat pump compressor dual run capacitor

I also tested the outdoor heat pump compressor dual run capacitor. It is rated 7.5/60 MFD x 370 VAC, and tested to 6.8/64 MFD. Is the 6.8 MFD value for the indoor fan a concern?

Also, the thermostat LCD display is fading at the same time. Could this be related to the problem, too? I did however check that it is receiving 24 VAC from the blower transformer.
 
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Old 06-03-07, 11:36 PM
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Tested Control Board COOL-H terminal 80 VAC only

I have tested the control board COOL-H terminal (which is connected to the cool (black) wire to the blower motor) at 80 VAC instead of 120VAC while the blower is running. Does this mean that the control board is defective, or the motor itself?
 
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Old 06-04-07, 10:04 PM
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Fan Motor bad, replaced

Thank you for all the helpful information. I finally had to call the AC guy and he tested the fan motor Amp draw too high and figured I had a bad motor. Changed the motor and capacitor now running good again. It was a good learning experience though but I guess changing the motor myself would have been too difficulty anyway.
 
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