New Air Conditioner injecting EMI/RFI noise into household power lines
 

Earlier this year I replaced my aging furnace and A/C units with new Carrier Infinity systems. They came highly rated and recommended. The furnace worked great over the winter and I'm very happy with it. Same feedback on the new air conditioner with how it has kept the house much more evenly cool over the summer, plus a nice drop in our summer electrical bill.

HOWEVER...

The new A/C is a 5 speed variable motor and I believe it is injecting electrical noise back into the breaker panel and spreading it into the electrical wiring in the house. This only happens when the A/C is turned on, just the furnace or the fan is no noise. I'm getting a high pitched whine from my PurePower 2000 that is beyond annoying and intermittent noise coming through my speakers off and on that wasn't there before. I have multiple PS Audio Noise Harvesters plugged into the outlets in the room, and they light up like a Christmas tree when the A/C is on, and go almost dark when it's off, so I have at least a visual verification and validation of what is going on.

I've been working with the local A/C company, and they had an electrician come out to check the breaker panel, wiring, grounding, tried switching phase, and none of that has made any difference. I wanted to reach out to the AA community and see if anyone has seen or heard of this type of issue, and if anyone has any suggestions or recommendations. I've done a lot of searching and reading online, and there isn't too much out there outside of an article or two on a couple of HAM radio web forums. I'm still doing some more investigating and researching on those.

Thanks, and I look forward to everyone's thoughts and suggestions!

Jeff.......From what you have described it appears the EMI is most likely originating in the compressor. You said no noise from the furnace, and no noise from the air handler fan, so that pretty much narrows it down to when the A/C compressor is running. I think you may want to begin by trying some EMI ferrite split snap-on cores on the compressor's in-coming 240 volt conductors. Install them on both of the 240 volt power wires just above where the wires terminate in the compressor. I would probably put a pair on the incoming power to the air handler, as well. Split ferrite cores provide excellent common and differential mode EMI suppression on round cable and wire assemblies. They are inexpensive, so experimenting with them won't break the bank or be a huge disappointment if they do not help.

https://www.alliedelec.com/product/l...B&gclsrc=aw.ds

Jeff... I think you told me you have dedicated outlets for your audio system. Do you have one or two electrical panels?

If you have two, I would confirm and or try to separate the AC unit and your audio gear.

Dan... I am a huge believer in Ferrites. :yes:

https://www.audioaficionado.org/atta...1&d=1568930812

https://www.audioaficionado.org/atta...1&d=1568930818

https://www.audioaficionado.org/atta...1&d=1568930825

Ivan.......It certainly appears you are.

I am hoping my suggestion solves the problem Jeff is experiencing.

Why does this not surprise me! :D

New Air Conditioner injecting EMI/RFI noise into household power lines
 

Does your Infinity system include an outdoor unit that features “Greenspeed Intelligence” ?

If it does, the compressor is driven by a variable frequency drive (VFD). The VFD takes the AC, converts it to DC, and then back again into variable frequency AC to run the compressor motor.

Most VFD’s are, as us audio geeks would say, Class D devices except the chopping frequency is 1 to 2 kHz instead of ultrasonic. All the crap they generate is in the middle of the audio band!!

There are two things to check.

First, the VFD ground must be bonded to the motor frame with a low inductance copper strap. They may have left it off in the factory.

Second, you may (probably will) need to install a VFD EMI filter between the compressor and your house wiring. Since the VFD is connected across both phases it will pollute everything.

These VFD filters are called passive harmonic filters. Carrier will need to provide a recommendation or better yet provide a filter and install it free of charge.

The nuclear option is to pull the outdoor unit and replace it with a standard single or two speed one without a VFD.

Ferrites, as useful as they are, will not solve this problem. To use a highly technical term, you will need a big ass filter.

Tom

Thank you Dan! This definitely helps to validate what I thought might be the logical next step, and I appreciate the help.

Here is what I found on one of the Amature/HAM radio forums that confirms your advice: http://www.arrl.org/forum/topics/view/46

The noise coming from the unit could be either common-mode or differential mode in nature (see http://www.arrl.org/files/file/Techn...age/Hallas.pdf).

More than likely, the noise is being conducted onto the ac mains. It could also be conducted onto other wiring such as the thermostat wiring although this would be unlikely, especially since it didn't change with grounding of the unused pairs, which would probably would have made a difference (for better of for worse) if the noise were on the thermostat wiring.

If the noise is common-mode in nature, you may obtain some relief with a common-mode choke. Obtain an FT-240-31 ferrite core (Amidon, Dan's Small Parts, Palomar) and wrap about 10 turns (if possible) of the ac wiring supplying the unit onto the core. You will need to include hot and neutral leads, plus the ground wire. You can also use -43 ferrite mateiral.

It will probably be necessary to cut the wirng and install the common-mode choke using wire nuts. This should be done by a qualified electrical contractor or installer. A serious shock hazard exists on the electrical wiring, and incorrectly done, the system could pose a serious safety hazard!

Considering the frequencies involved, you may be able to use clamp-on ferrite chokes and obtain some relief. Make sure they are either -31 or -43 ferrite material. You would need five to 10 of the larger clamp on ferrites to provide much effectiveness at upper HF. At lower frequencies, even more would be required. Still, they may be a good troubleshooting tool.


I'll forward this information to the A/C company and the electrician, and I will report back on the results.

Thanks again, Dan! :thumbsup:

One electrical panel feeding 4 dedicated 20A circuits into the room. I've thought about doing a dedicated sub-panel to see if that helps, but the electrician didn't think that would resolve the current issue.

Doesn't surprise me either... :no: :D

Thank you very much for the additional advice. I don't believe I have a Greenspeed unit, but I will double check.

If it comes down to it, I will have the unit replaced with a lesser 2 speed fan unit that does not generate EMI if I have to.