Thoughts... **thermostat unit is wall-mounted -- connected to the furnace by
approximately 50 feet of wiring. **
That's a pretty good ANTENNA -- and when the thermostat sends what looks like a
valid command, chokes at the furnace inducer may (If it works) let it pass.
Opinion: Your 40 meter RF *shouldn't* burn out the motor it encounters an RF
spike, but that could zorch the inducer electronics, which (if I understand)
may be likelier to fail.
Cortland -- ex EMI/EMC, now retired
-----Original Message-----
From: Alan Higbie
Sent: Oct 20, 2021 4:04 PM
To: Rfi List
Subject: [RFI] Could RFI from my transmitter cause the failure of a furnace ECM
inducer?
Our gas furnace has a problem - and I wonder if there is potentially a
connection between RFI from my transmitter and a failure of a furnace ECM
inducer.
Symptoms: (1) when turning on the thermostat for heat; (2) the fan comes
on; but the gas burner does not ignite; (3) therefore, no heat comes out.
There had been a neighborhood power outage the night before we noticed the
problem most recently two days ago.
The HVAC technician came yesterday on a trouble call.
The technician reports: "Tested furnace and found inducer not running.
Checked that there was high voltage and control voltage. Inducer is ECM.
Checked the fault history on the thermostat and found the inducer has
failed 127 times today. [yesterday] I would recommend replacing the inducer
assembly / ECM motor."
Reference furnace model is Carrier 59MN7A120V24-22. Installed 9-1/2 years
ago.
This problem came up once before, last April 2021 (at end of the last
"heating season") right after a neighborhood power outage. At that time I
read an error code which said: "42 - Inducer Motor Fault." After a while
the furnace started heating again. But, the furnace didn't get used during
the summer until last week.
Now we can't get it restarted and are looking at replacing the failed part
or, ugh, the furnace.
The thermostat unit is wall-mounted -- connected to the furnace by
approximately 50 feet of wiring. After a family member reported "clicking"
from the furnace I placed some snap-on ferrite #31 material at the furnace
end of this control line - this was about 16 months ago. I have not yet
measured the RF current in that control line (although I do have the
instrument).
QUESTIONS
Has anyone experienced damage to furnace from induced RF?
Could there, theoretically, be a casual connection between 1500 watts out
at 14 MHz and the failure of a furnace Inducer Motor / ECM?
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