[RFI] Lennox brand HVAC RFI experience

[Jeff Blaine]

Thanks for that link Steve.  It looks like this Lennox heater uses 
exactly that 5-speed constant torque motor.  In looking at how those 
motors are constructed, and the layout of the control board, I don't see 
any sort of thing that screams "PWM IMPLEMENTED HERE SO LET THE WAVEFORM 
CHOPPING CONSOMME AND LETS RIP SOME RFI!!!"

I had a long talk with my HVAC guy, and showed him the shack, and the 
test gear and so he was comfortable that I would be able to implement 
any abatement - if needed - especially since any 120/240 stuff would 
have my electrician's seal of approval and keep them off the hook for 
"user tampering" or whatever other things they may be worried about.  
And from that, we did not talk about any of the variable speed this and 
that solutions out there.  It was all single/dual speed only.  No 
variable anything.

I've got a few messages from guys saying the RFI issue was contained (in 
those cases) by following the generic suppression stuff (common mode 
primary, some differential if needed - and a bit of shielded runs to the 
thermostat in one case).  I suspect that I could make a variable speed 
system work but it looks simpler and may be a higher chance of 
no-problem if I just stick with the dual speed options which is where I 
am now.  In fact, I may consider a 2 speed aircon compressor if those 
are winding-selected 2-speed implementations instead of 2-setting 
variable speed things.  Need to check more.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 7/18/22 6:57 PM, Steve London wrote:
> This is certain to raise W0LEV's blood pressure:
> http://library.coburns.com/HVACTechTips/Motors%20what%20is%20going%20on.pdf
>
> GL finding a new PSC-motor furnace and compressor. If you find one, 
> please post it - I'm in the same position as AC0C.
>
> 73,
> Steve, N2IC
>
> On Mon, Jul 18, 2022 at 3:55 PM Jeff Blaine <KeepWalking188 at ac0c.com> 
> wrote:
>
>     We are looking at a replacement HVAC and these items are proposed for
>     the install.  I'm paranoid about the RFI noise profile out of modern
>     HVAC systems and would be interested in any comments.
>
>     The Lennox P/N recommended are:
>
>     Merit series - ML14XC1$-042 compressor 14 SEER
>
>     Elite series - EL280UH090E488 dual-speed (2-stage?) furnace 80%
>
>     The installer is aware of the Lennox 604552-01 kit which includes a
>     differential filter and a snap-on toroid.  I've made it clear that
>     the
>     single snap-on toroid is likly and that a multi-turn type 31 would be
>     used in lieu if needed.  Which would not have a warranty issue as the
>     HVAC guy and I share a common electrician who has vouched for the
>     safety
>     of this "mod."  And we have discussed that similar (multi-turn
>     toroid)
>     treatment may be added to the thermostat line as well.
>
>     Appreciate any advice on other guys who may have experience with
>     Lennox
>     gear in general, or these families in particular.
>
>     73/jeff/ac0c
>     alpha-charlie-zero-charlie
>     www.ac0c.com <http://www.ac0c.com>
>
>
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