Interference from A/C unit... - Home Theater Forum and Systems -

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post #1 of 14 Old 09-04-08, 08:57 PM Thread Starter
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Interference from A/C unit...

Strangely enough... when our central A/C unit turns on, we get interference in our 67" LED DLP display when it is tuned to a particular OTA HD channel. Actually it has to be interference in the satellite unit or OTA antenna, which has only recently started to happen. We do not remember it happening until setting up the great room system. I suggest the satellite receiver or antenna because there is no interference when watching a DVD. The OTA antenna is connected to the satellite receiver, which has the ATSC tuner.

I did mention to the satellite guy when they came to check out our previous malfunctioning receiver. He suggested it may be because the satellite and antenna is grounded with the A/C unit. They are all at that end of the house. But again, this has never been a problem before... it has just recently started.

I have the satellite receiver and display plugged into a UPC backup, but obviously that has no filtering of any sort.

Is there a 75 ohm filter that would knock out the interference... or should I be looking to prevent it by eliminating the source?

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post #2 of 14 Old 09-05-08, 09:40 AM
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Re: Interference from A/C unit...

This is a strange one
Just out of curiosity have you tried plugging the equipment into another circuit in another part of the house with an extension cord? It could be because your system and the AC are on the same leg of the electrical panel (there are two).

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post #3 of 14 Old 09-05-08, 09:57 AM Thread Starter
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Re: Interference from A/C unit...

I have not tried that, but probably should. I actually thought about those two circuits being on the same leg and forgot to look. I was thinking if they were that I could move the 20 amp circuit to the other side... I have a couple of empty spots. Still weird that it just started, but maybe it has something to do with drawing more current from that circuit than previously... but then again, several years ago we had a whole lot more equipment in there than now. Hmmm... and that whole lot more equipment was on a dedicated circuit, possibly the other leg. I need to check that.

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post #4 of 14 Old 09-07-08, 02:40 AM
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post #5 of 14 Old 09-07-08, 07:08 AM
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Re: Interference from A/C unit...

Central Air is usually on a circuit all by itself.
Yeah, but even though a device may be on a seperate circuit, it can interfere if it's on the same leg. There are two 120v legs in a service panel.

But, in this case, that won't be the problem, since air conditioners use both legs - they're 220 volt devices....

You'll have to start messing around with the antenna to narrow down the problem. Try moving it temporarily and try a different lead cable route for starters.

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post #6 of 14 Old 09-07-08, 11:58 AM
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Re: Interference from A/C unit...

If the interference is only on a particular OTA channel it is almost certainly RF and not necessarily on the electrical system. Filtering or shielding at the source would likely be needed. I would be fishing around the ac unit with a signal stregnth meter looking at the frequency that the affected channel is on to identify where it is coming from.

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post #7 of 14 Old 09-07-08, 12:47 PM
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Re: Interference from A/C unit... strange I saw this as I was about to post that when my central air kicks on or off I get a burp from my sub, but not my speakers?!?
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post #8 of 14 Old 09-07-08, 02:40 PM
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Re: Interference from A/C unit...

I would suggest checking the start and run capacitors on the ac's compressor. Sounds like the run capacitor is going bad which can cause the motor to generate rf interference.
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post #9 of 14 Old 09-07-08, 05:50 PM
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Re: Interference from A/C unit...

Hi Sonnie,

Do you want your Panamax units back? Sorry, they are superglued to the equipment rack.

As an electrician, I have a few suggestions....payback time for the chairs.....

First off, I would check your grounding electrode conductor (ground wire) coming out of your meter can or breaker box and make sure there is a good connection to your ground rod. Weedeaters and lawnmowers can and do make these connections loose or even break them off of the ground rod.

Your dish guy said you may have a problem because it is grounded on the same ground circuit with the a.c. unit. It is supposed to be!

All circuits in the home are required by NEC to be grounded back to the grounding buss bar in the main panel. Make sure that the grounding and neutral (white) wire screws in the panel are tightened. Turn off your main breaker before performing this task. I call this procedure a "panel tune up".

After many years in this business I've seen some strange things happen like meters turning without a load and etc. If you are comfortable with working in your breaker box, your ac compressor unit is on a two pole 30 or 40 amp breaker. I might move it across to the other side of the panel if you have room. You may have to swap breakers. There could be some inductance causing the problem with wires and breakers next to the ac breaker. Make sure you turn the main off with this procedure too.

The ac unit is 240 volt using both legs of electricity supplied by your power company, so that eliminates the issue of switching legs. Your blower in the attic if your heater is gas or propane is on a 120v circuit and only uses one leg, so moving it in the panel may help. If it is electric, you probably have a two pole 60 amp and a two pole 30 amp breaker for the heat, but you haven't used it this summer so we can eliminate that one.

Sparky77 suggested changing out the start and run caps in the ac unit. Now they are usually a single capacitor that handles both the condensor fan motor and the compressor all in one cap. That is a possibility.

I have recommended to some customers that have lights blinking at start up that are now using the scroll compressors to contact their ac company to install what is called a "Hard Start Kit". That kit should have the new caps and everything you need and usually stops the dimming at start up.

All gas and metal water pipes also are required to have a #8 solid copper bonding wire connected to the breaker panel's grounding buss bar. All of those pipes in the attic are a giant grid recieving rf signals from radio stations, but the reason for the bonding to the panel is for personal safety in case a rodent chews a wire and it touches the piping.

Make sure your dish and OTH antenna are grounded.

If you need me to come out to make a service call, I'm free this week. My time starts from the time I leave until I get back to the shop.

Let the group know what you finally found as the culprit so we all can benefit from your experience.

Update....I just read your original post again and you started experiencing it when you went to the great room. See if the great room breaker and ac breaker are next to each other. If so, move the great room circuit breaker a few spaces away.


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Last edited by Mike Cason; 09-07-08 at 05:57 PM.
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post #10 of 14 Old 09-08-08, 04:31 PM Thread Starter
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Re: Interference from A/C unit...

I checked the AC breaker (40amp double pole) is actually on the opposite leg of the great room receptacle.

I did not realize it until I looked, but the display, receivers and DVD player are all on one dedicated circuit. I wired it, but just did not remember.

We are all electric and the water lines are in the ground.

We have had some issues with our condenser/fan/compressor unit outside. On two occasions we have come home to a warm house this summer because the lead wire to the compressor had came lose and grounded to the housing, causing the outside safety breaker to trip. We had to fix that twice. Another time here recently it tripped, but all wires were in place. Something may be up with that.

We do get lights dimming on AC start up as well. Maybe one of those start up kits will help with that, if nothing else.

I still need to check all the grounds though... been lazy.

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