Given Trane's attitude and the fact that you have localized the problem to
originate at the induction blower, I would replace the motor leaving the
existing associated parts intact if possible (impeller / squirrel cage /
overtemp thermostat, etc) or replace the entire assembly which includes the
motor and associated parts entirely. Having replaced two of these myself, I
know this is likely to be a $175 item or more. Adding EMI filtering requires
more measurement and experimentation than most people are willing to try,
IMHO, so I am reluctant to suggest designing your own EMI filter by trial
and error. Wrapping some foil around the blower housing (being careful to
avoid shorting out any attached thermostats / safety switches / may help if
the motor itself is radiating (as opposed to conduction out through the
wiring harness).

Smarty


"MLD" wrote in message news:CsO4h.3626$Ue.913@trndny03...
Just to remake the point---the problem is, without question, the inducer
motor. The "new shielded" harness put in my furnace still had, in my
opinion, a major flaw. The wires at both connector ends was unshielded
for
approx 1 inch. So all the wires, at both ends, was exposed to picking up
and/or radiating any RF noise. I shielded, using foil, the exposed wires,
grounded the harness shielding to the furnace, my earth ground, water pipe
and control board grounds. Nothing got rid of the noise problem. You
offer
some potential fixes but its apparent that Trane isn't interested in
putting
any effort into resolving the issue.
MLD

"Smarty" wrote in message
...
This comment opens up the possibility that wrapping the existing harness
with a braided wrap as a helix and then bonding the outer braid to a good
earth ground may help the radiated electromagnetic interference (EMI).
The
conducted noise will still need to be filtered / trapped before the
wiring
enters / exists the furnace. Given that this EMI goes from the AM band
(approx 1 MHz frequency all the way up to VHF or UHF television
frequencies,
however, the likelihood of being able to devise a good wideband filter
which
substantially reduces the conducted EMI is remote without a lot of
expense.
If the motor itself is truly the principal noise source, then getting
some
noise suppression right at the motor offers the best solution, either
with
shielding, series inductors (chokes), shunt capacitors, or all of the
above.
The motor brushes and commutating connections may be creating a lot of
arcing, and a new motor may help if it is constructed differently (from a
different vendor).

Smarty


"MLD" wrote in message
news:d6J4h.3603$Ue.2593@trndny03...
Looking back, I now recall that replacing the inducer motor wiring
harness
with one that had better shielding did make a significant improvement
although it didn't completely resolve the noise problem.
MLD


"MLD" wrote in message
news:q0J4h.5540$qG.1024@trndny02...

"modelman" wrote in message
oups.com...
Several months ago I had a high efficiency Trane XV90 natural gas
furnace and heat pump installed. Since the weather has recently
been
cold enough for the gas furnace to provide heat, I have been
experiencing severe radio interference. The interference wipes out
AM
broadcast reception throughout my house. I also see snow on a TV
connected to an external antenna.

The radio noise occurs as soon as the draft inducer motor starts up;
the pitch of the interference is related to the motor speed. The
draft
inducer motor is a dc motor driven by a PWM controller on the main
circuit board. It is well known that PWM systems generate strong
harmonics throughout the radio spectrum, resulting in radio
interference. However, properly designed PWM systems include
filtering
and shielding to suppress the radio frequency currents from the
wiring.

I contacted my installer, who is totally unfamiliar with the
problem.
The electrician who was sent to my house to investigate the problem
also doesn't understand what's going on. I had to explain the
difference between an RF ground and dc or house ground to him.
Although everything appears to be well grounded from a dc
perspective,
I suspect that portions of the system are radiating RF energy.

Several days ago I emailed Trane about the problem, but haven't
received any response.

Although there has been past discussion in this group about radio/TV
interference emanating from Trane high efficiency gas furnaces, I
haven't seen any definitive fix. Does anyone know if Trane has a
fix
for this problem. Do they have a shielded cable and or rf filter
kit
to suppress this noise? Since my system is under warranty, I won't
attempt any modiifcations to the system.

Has anyone experienced this problem?

Thanks.


Here's one guy that had the exact same problem. I was a bit luckier
that
you in that it didn't bother my AM radio signal but it did screw up my
kitchen TV picture--rabbit ears. It's coming from the inducer motor
as
you
surmised. The installer was very cooperative and tried to fix it
based
on
input from Trane. Changed out the cable to the motor with one that
was
supposed to provide better shielding and when that didn't work changed
the
control board---both without any success. Prior to and after
component
replacements I tried grounding everything that I could, again with no
success. Got the local Trane Rep on the phone; he made promises but
never
followed through with a solution. Had a new Trane for about a year
that
got
into a problem resulting in it being replaced under warranty rather
than
repaired--it was the replacement furnace that had the RF noise
problem.
Found out that Trane went to a "new design" inducer motor. I tried to
get
the Trane Rep to replace the motor with the same design that was on my
first
furnace. No luck there, was just ignored and yessed to death. If
Trane
acts
dumb about the RF noise it's all show-because mine happened about a
year
ago. My guess is that you're stuck with the problem. I finally made
mine
going away by putting in a cable line to the TV.
My suggestion in your tussle with Trane or the installer is to go find
an
inducer motor from an earlier vintage furnace. Even if it has to be
cannibalized off an older (2yrs or so) furnace.
MLD