I have a 2004 Carrier furnace with a variable speed motor. When I resumed
ham radio in 2015, I found it did produce RFI. I could watch the spectrum
change as the motor ramped up in speed. I installed a Corcom filer on the
AC line as it enters the furnace and another one at the motor. However,
that was only partially successful. I put #31 cores on the line to the
thermostat and the line to the A/C compressor (that energizes the 24 VAC
contactor). That eliminated the remaining RFI. In my case, just clamping
one core on those lines was enough. I know that multiple turns through the
cores increases the impedance with the turns squared and I was ready to
splice the wires if I needed to do that. But, I did not. The lesson
learned for me on that appliance was that every wire exiting an appliance is
a potential RFI radiator, not just the power chord.
A lesson learned on previous RFI and isolation problems in my engineering
days is if you try something and it does not help, don't assume it is not
contributing to the problem (and cross it off your list). It could be the
strongest leakage path is masking the weaker ones, and you could end up
taking a long time to go back to something you ruled out before. A better
approach to save on unnecessary filters is to solve the problem and then go
back and experiment with which filters (e.g. ferrite cores) you can remove.
Good luck with your RFI efforts,
Randy KQ6RS
-----Original Message-----
From: RFI <rfi-bounces@contesting.com> On Behalf Of John Pelham
Sent: Wednesday, February 20, 2019 10:17 AM
To: 'Kelly Jones' <kjones@virtualcohesion.com>; rfi@contesting.com
Subject: Re: [RFI] Air Conditioner / Heat Pump recommendations
Back in 2010, I replaced a heat pump with a new Trane. I specifically asked
the contractor for a unit with a single-speed motor. What I got was a unit
with a "single-speed motor," but it was an ECM (electronically commutated
motor). It generated lots of RFI. I think Trane offered an RFI-kit, but I
chose to fix it myself with some #31 ferrite cores. I was mostly successful,
although interference could still be weakly heard on some HF bands.
You can get lots of info on Trane products by searching. I Googled "trane
4WCZ6036B1000A" and got specs and wiring diagrams, which I only skimmed. You
might want to dig into more detail. I did see the sentence "This enhanced
mode selection provides a ramping up and ramping down of the indoor blower
speed to provide improved comfort, quietness and potential energy savings."
The accompanying graph shows ramping between 2 stages. I think it is likely
that your recommended unit contains an ECM motor, and yours appears to be
operated as a variable speed motor - how else to get the ramping between
speeds? And even if there wasn't ramping, in my experience an ECM motor
operated at a constant speed is just as noisy as one in a variable speed
system.
73, John W1JA
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Kelly Jones
Sent: Tuesday, February 19, 2019 8:41 PM
To: rfi@contesting.com
Subject: [RFI] Air Conditioner / Heat Pump recommendations
Hi all,
I'm needing to replace an old Carrier air conditioner/heat pump and would
like to ask the general experience of the group. Have you replaced a unit
recently? If so, what make/model did you use? Did you have any issues with
hash/birdies/noise after replacement?
I'm being recommended an American Standard (Trane) 3 Ton, 16 SEER package
heat pump. The model is 4WCZ6036B1000A. It is not a variable speed drive,
but it is 2 stage. I'm hoping to not make a multi-thousand dollar mistake
by installing a noise generator.
73
Kelly - N0VD
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