New Furnace Electrical Noise Problem

[MLD]

Have a new High Efficiency Trane Gas Furnace. Every time it fires up the picture on a TV set (rabbit ears antenna) on the floor right above it goes haywire. The picture becomes almost unwatchable because of all the noise streaks and snow in it. The source of the problem is the Vent Blower (Inducer motor)--the electrical noise is only present when it runs. So far, following Trane's service Tech instructions, the HVAC Co techs have done the following:

1. Checked to make sure that there is a good ground between the furnace and the earth ground.
2. Replace the wiring harness to the vent blower with a shielded harness--Trane may call it a shielded harness but the shielding ends about 6 inches from the motor. So there is 6 inches of unshielded wiring which to me is like not having any shielding at all.
3. Replaced the control board. Why they haven't suggested replacing the Vent Blower is a mystery to me. However, while there has been quite a bit of improvement the TV noise problem still exists. Now waiting on the results of a discussion between HVAC Co.and Trane. I've been told that I'm not the only one that has experienced this problem. Has anyone else seen something like this? MLD

[Brian O]

Isn't there some sort of capacitor (condenser) associated with these motors? Being an electronic technician, that would immediately draw my suspicions. B

[Bob Pietrangelo]

It depends on the model of the equipment XV90 has a variable speed inducer, XL80,XV80,XL90 all have 2 stage inducers. We need more info. Don't thye have cable or dish in your neighborhood. What happens if you move the TV, shouldn't be hard with no cable. Does it do it the entire time the equipment is running or for a shorter period of time. If it is a 2 stage system does it hapen on low and high fire.

[Mark]

Is this a motor with brushes, I would doubt it.

A motor without brushes (like a fan) should not cause any TV interferecne at all. A motor with brushes (like a drill) will be very difficult to prevent the interference.

Is this a gas or oil furnace. If it is oil, it may be the high voltage ignitor and not the blower that is causing the interfrecne. This may be easier to cure.

Mark

[Bob Pietrangelo]

Trane just came out with their own oil furnace this year. At least where I am.

[MLD]

Sorry or the top post: In response to your comments-The furnace is a gas fired XV90 with a variable speed blower. The noise/interference problem begins as soon as the inducer motor starts to rotate, well before the furnace fires and before the main blower starts. The noise remains until the inducer motor shuts down even though the main blower is still running. I ran the blower only (set the system on Auto) with nothing else operating (no call for heat) and there was no interference problem. This is the second XV90 furnace, the first one was replaced after being in service for about a year, per Trane, when it developed an internal condensate water leak problem due to poor welding. No noise/interference with that furnace and interestingly enough, the first thing noticed when the current one was being installed was the fact that the inducer motors, old vs new, were completely different looking configurations with respect to one another. Yes I have cable and haven't tried experimenting with the TV location as it is academic--The interference is still there and now I can use it as a good indicator with respect to the success of any proposed fix Most electronic equipment must meet specific FCC requirements with respect RF generated noise. Does anyone know if something like this falls under the same guidelines? MLD

[Ralph Mowery]

Most everything that can cause interferance with the radio or TV is under somekind of FCC rules or athority. The furnace company may have a solution for it . If they do not have an addon or filter for it, then request they replace it with one that does not cause a problem.

YOu may be able to look under

for some information.

[Mark]

Are you saying you are getting this interferecne fomr the inducer motor and you have CABLE TV?

You say the inducer motor is variable speed?

Is it continuously variable like a drill or does it have say 2 speeds that can be selected?

Is there an electronic device that controls the speed?

Mark

[MLD]

This particular TV is a small one used in the kitchen and is not connected to the Cable. It uses rabbit ears. As an aside--before some of the fixes were put in place, the RF noise was also picked up by a radio located within

10 ft. of the furnace--lots of static that would go away when the inducer motor stopped. I don't know the specifics about the inducer motor with respect to whether or not it is a variable speed motor. Makes no difference, however, since the RF interference starts as soon as the motor does. MLD

[Mark]

OK, not cable TV...

I think you want to determine if it is a brush type motor and the sparking at the brushes are casing the prob or if it is a variable speed motor controlled by electronics like a lamp dimmer in an electric drill and maybe the electronics are casuing a prob.

Does the motor change speed. Does it seem like an electic drill motor or a fan motor.

Mark

[Mark]

Probably your best bet is to run a cable TV drop to your kitchen TV.

But it is a shame that these new products are designed without consideration about RF interference.

Mark

[MLD]

Thanks for you comments, however, don't want a cable connection in the kitchen (not convenient for routing a cable) and do not want to compensate for a poor design. Also don't care what kind of motor it is as there is nothing I can or will do to fix it on my own. This has to be resolved by the manufacturer. Will continue to work with my HVAC Co and go after Trane to provide a resolution. Having said all that---the biggest improvement came when the motor wiring harness was replaced with a "shielded" harness. As I noted in an earlier post, the shielding stops about 6 in. or so from the motor. My own work experience indicates that even an inch or so of exposed wire is more than enough to pick up these noisy RF signals and create a problem. If I can lay my hands on some braided wire mesh I will cover the exposed wiring and see what happens then. MLD

[Gideon]

MLD,

My impression is that you expect the installer to eliminate any unreasonable RF that the equipment is producing, and that you are seeking advice and experimenting to aid the HVAC company in finding & fixing the problem. I agree - in your situation I'd do the same.

Also, I agree with you about the cable drops. We've got 5 TVs connected to cable, but we've also got a few that aren't. I don't want those on cable for a variety of reasons - too much splitting of the cable signal, difficult cable runs, appearance, etc. Even if extra cable drops would fix the problem, I'd still want the furnace not generating all that RF.

Suggestions:

1) Just as a sanity check, use a portable battery operated radio to see how much noise it picks up from the furnace. From what you have said, I'd expect that it would also have a problem. But you want to confirm that the interference is coming through the air and not through the house wiring.

2) Experiment with the shielded harness. Seems to me that you could use some aluminum foil to carefully extend the shielding another 6 inches. If that helps substantially, then get the HVAC folks to do it correctly. I'd also want to know why the harness is generating so much RF in the first place.

Good luck, Gideon

======================

1. Checked to make sure that there is a good ground between the furnace and the earth ground.
2. Replace the wiring harness to the vent blower with a shielded harness--Trane may call it a shielded harness but the shielding ends about 6 inches from the motor. So there is 6 inches of unshielded wiring which to me is like not having any shielding at all.
3. Replaced the control board. Why they haven't suggested replacing the Vent Blower is a mystery to me. However, while there has been quite a bit of improvement the TV noise problem still exists. Now waiting on the results of a discussion between HVAC Co.and Trane. I've been told that I'm not the only one that has experienced this problem. Has anyone else seen something like this? MLD

[MLD]

"Gideon" wrote in message news:rlRZd.19573$ [e-mail]...

Nice comments--small kitchen TV, not practical to hook it up to cable as the wire would end up being exposed in a dining room and also be in the way of other things,. I've already experimented with some of the things that you mentioned. I have a radio within 10 ft. of the furnace that is definitely not on the same circuit as the furnace. Initially it would produce enough static to almost drown out the sound whenever the inducer motor started up. It's much more quiet now for whatever reason. I will try a battery powered radio and see what that does. Early on I did take some aluminum foil and loosely wrapped it around the wires close to the motor--- no improvement. Will try to improve on this approach if I can find some braded (mesh) shielding. Almost positive, but to close the loop I do need to verify that the furnace and TV are not on the same circuit. In case you missed earlier comments, this is a replacement furnace, original was only one year old,experienced a failure that resulted in Trane recommendig its removal. No RF problem with the original furnace. The significant difference between the two of them is the inducer motor. The newer one is bigger and with the housing slotted such that you can see the motor windings. With respect to the wiring harness, I can understand shielding it so that it wouldn't pick up stray signals that could impact the behavior of the furnace controls. I don't understand, however, why the wires would radiate signals---I still would like to see the motor replaced. So faar, Trane has taken the shot-gun approach to troubleshooting. MLD

[Mark]

If you put foil around the wires, you have to extend the foil to the shield to ground it. Ungrounded, the foil will do very little. Be very careful that you don't short anything.

Mark

[Jim]

I have a brand new high efficiency AUY American Standard furnace, which is exactly the same as the Trane XV90, except for the exterior label. It has a variable speed fan motor and a variable speed exhaust (aka draft inducer) motor. I've noticed the same thing that you have, the draft inducer motor makes a lot of e-noise. The noise starts as soon as the inducer motors starts (e.g. before the burner lights and before the blower motor starts) and ends as soon as the inducer motor stops (e.g. when the burner shuts down but the blower is still operating), so I've determined the inducer motor is the source of the noise.

In my case, we have cable TV and I've only noticed the noise on AM radio. The noise is quite on all stations except for a 50,000 W station 2 miles away, and even on that station the furnace noise is audible in the background.

I haven't complained about this noise yet (trying to get a sizing error fixed) but am interested in any resolution to this problem---you're not alone!

[Jim]

Correction: noise is quite *loud* on all stations.

I should add that the American Standard AUY (also known as the Trane XV90) furnace series is a natural gas furnace with a variable DC brushless blower fan motor. The inducer motor is variable too, but it may be a brush type motor, causing the noise. It must be quite a bit because it causes interference on the radio in my car as I approach the house.

[Tony Hwang]

Hi, Ever tried ferrite core chokes to suppress noises or bypass caps? Tony

[MLD]

Yesterday I took foil and wrapped the exposed harness wiring closest to the motor and did the best I could to make sure that it was touching the harness shield. I also wrapped foil around the motor housing--just long enough to determine if it effective or not. As far as I could tell there was no discernable change. Still waiting on Trane to come up with something. MLD

[MLD]

If you've read one of my earlier posts you'll see that replacing the wiring harness between the inducer motor and the control board (with, per Trane, a shielded harness) made a significant differnece in the RF interference in the TV picture. Didn't eliminate it though--at least this gives you some direction with respect to trying to fix the problem. MLD

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