[RFI] Thermostat/HVAC Susceptibility

[Brian Moran]

Dan you may want to check to see if there is any low voltage cable out to your compressor in addition to the power. There was to mine. The cable was driven by solid state electronics; I surmise that RF got in to this cable, rectified, then triggered the compressor’s contactor in time with CW, while the AC was really off. Eventually the contactor contacts welded. And the thermostat base where the electronics were (Nest) was damaged. 
Brian N9ADG
Sent via iPhone

> On Jan 7, 2026, at 5:16 PM, Dan K2YWE <dan.k2ywe at gmail.com> wrote:
> 
> FYI,
> I ordered several 1", 1/2", and 1/4" ID 31 mix Fair-Rite clamp-on (SnapIt)
> cores today for this and to have for other applications.
> I'll let the group know what worked. I will try several turns on the larger
> core first. I don't think I'll have to treat the wire out to the A/C
> compressor since I've been assured that there are no electronics out there,
> just contactors.
> Thanks for your advice thus far.
> 
>> On Wed, Jan 7, 2026 at 7:43 PM Jim Brown <jim at audiosystemsgroup.com> wrote:
>> 
>>> On 1/7/2026 1:03 PM, Dan K2YWE wrote:
>>> That's not surprising. My installer told me that Ecobee. I think,
>> provided
>>> a ferrite bead with their thermostat.
>> 
>> A ferrite bead MAY satisfy EMC requirements at VHF/UHF, but is next to
>> useless at HF and below.
>> 
>> Multiple turns must be wound around a Fair-Rite #31 core, and they must
>> be wound in sequence around the core, to be effective at HF and below.
>> 
>> 73, Jim K9YC
>> 
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