lennox - lights fine, blower mostly hums

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Old 01-02-08, 10:04 AM
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lennox - lights fine, blower mostly hums

I have a Lennox Whisper Heat SP 745 gas, not sure of the year(around 10 years old maybe).

Ok, I've replaced 2 thermostats and the problem remains (first one was an old school round honeywell, now its a digital Hunter)

In the fan on position the blower runs only for a short time (10 min), then shuts off regardless if its up to temperature or not. Then it will "hum" for about 30 minutes before it decides to kick back on. If i go out there and manually turn the light switch off I can wait about 10-15 minutes, turn the switch on and the blower will work again.

If i have the fan switch in the auto mode, it rarely does anything, even tho i can hear the click in the thermostat recognizing that it needs to do something.

If i turn the light switch on to early then all i hear is a semi loud "click" from the (forgive me here) panel on the furnace that has 4 larger black capacitors/fuses not sure what they are.

When i run the A/C it all works fine, if that has anything to do w/ this.

thx for any help you can provide, just let me know if i need to add more to this.
 

Last edited by bm2thirsty; 01-02-08 at 10:20 AM. Reason: thermostat brands added
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Old 01-02-08, 11:50 AM
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Smile

Im going to say you have a bad speed in the motor, and the unit uses the same speed in the "on" position as it does in the heating mode, the A/C mode is most likly using the high speed in the motor and that is why you don't have a problem in cooling mode.(A/C).

I beleave that you may need a new motor.

The reason the motor runs for a short time then stops, is because the motor over heats and trips the internal overload , when this cools off the motor comes back on. You turning the power off to the unit starts the cooling process that much sooner.

The black squares on the panel are probly relays.

Capacitors have wires going directy to them and are usuly located close to the motor.
 
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Old 01-02-08, 12:22 PM
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Originally Posted by RoadrunnerofNJ View Post
The black squares on the panel are probly relays.

Capacitors have wires going directy to them and are usuly located close to the motor.
yea these have no wires, more like 1 x 1 "plugs" if you will. I was hoping since that where the clicking was coming from that they might be the issue. A new blower dont sound cheap

Thx for the info, I'm gonna start trying to price out some blowers and go from there...
 
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Old 01-02-08, 07:04 PM
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Whenever possible, you want to test the part you think is defective directly to see if it is working properly or not.

For a fan motor, that usually means applying the 120 VAC operating voltage to the motor and finding out if the motor comes up to speed and run properly or if there is some defect or problem with how it operates.

Other things to check would be to check to see if the motor turns freely, or whether it binds. Another routine check would be to see if the motor has oil ports, which suggests it should be oiled from time to time.

If it hasn't been oiled, that can explain why it wont come up to speed. If you oil it and can get it to turn under power, let it run for a while and see if it runs OK. Somtimes it will, sometimes the motor has been damaged and will slow down or overheat and shut off.

Most motor have to be removed entirely from the fan housing to oil the inside oil port, but doing so is essential.
 
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