New Furnace RF Noise Problem


Have a new Trane XV90 two stage condensing gas furnace. As soon as the Inducer motor starts up a TV in the floor above it has it's picture completely filled with RF noise--static, snow, all kinds of white lines through out. Initially, the picture was almost unwatchable.Important to note that the TV is using Rabbit Ears. To date, my HVAC Co per Trane's recommendations has done the following: Checked the 110 volt supply to insure that a good ground is in place. Replaced the wiring harness to the inducer motor with a "shielded" harness. In actuality, about 6 inches on either side of the harness is not covered by the shielding. Replaced the control board. Significant improvement with the harness replacement but the RF noise is still there and still distorting the TV picture. There is absolutely no question that the problems appears as soon as the inducer motor starts running but surprisingly, Trane hasn't picked on it yet. HVAC Co now waiting on Trane for more direction. Looking for any comments or suggestions that I can pass along to my HVAC Service manager. He has been doing all he can in order to rectify the problem but at the same time must follow Trane's instructions in order to get paid for his time. MLD
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possible solution. Also thought that this might give you field guys a heads up on a potential problem that you might run into. Thanks anyway. MLD
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wrote:

RFI/TVI is usually caused by either a lack of filtering in really cheap electronics, or a grounding problem. Getting rid of the rabbit ears, and go to an outside antenna or cable will help if not eleminate the problem. Its also possible that the furnace was wired into the same circuit as the TV or vice versa.
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Just out of curiosity and general knowledge what sort of motor do they use that creates RFI? I presume this is not just a run of the mill little AC induction motor with one coil, a rotor and no brushes or electronics.
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Good question, IMO. I looked. The XV90 motors are variable speed. It ain't the motors, it's the drives (controllers).
I dunno, but I'd say noise being propagated up the neutral.... could be nasty for a lot of stuff like home computers and anything with a microprocessor in it.
IF the drives or controllers are properly grounded, and IF the unit is properly grounded, then you have harmonics left. Check the neutral/ground bonding at the service entrance, and be certain that the neutral/grounds are not bonded together anywhere else (common mistake).
Just my 2 cents worth. I'm just a dumb-ass electrician.
Jake
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The XV90 has a variable speed dc motor for it's inducer.
--
Bob Pietrangelo
snipped-for-privacy@comcast.net
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Bob,
Is it one of those 'brushless' designs? If so, there's a noisy (as in AC noise) drive behind it.
I'm curious...
Jake
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Try putting an isolation transformer on the furnace, These transformers are optimum for 60 cycles A/C, not RF that causes interference. Moving the breaker for the furnace in the panel farther away from the breaker for the TV ay help. Also, make sure the TV breaker is on one leg of the incoming power while the furnace breaker is on the other leg of the incoming power. Finally, put a low pass filter on the outlet feeding the TV. See if a TV repair man can get you one.
Stretch
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Get cable......Problem solved.

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What kind of TV is it? Is it a "westinghouse"?
If so, perhaps the wascally wabbit is just westing for a bit.
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Why in the hell would anyone use rabbit ears any more?
MLD wrote:

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    Well, let's say your were an ASHRAE Standard Bunny, and you didn't want to miss dinner time ......
wrote:

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Vicki Szaszvari posted for all of us....

--
Tekkie

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