Tony,

The interference is being radiated, since I can hear it loud and clear
on a "walkman" outside of my house. I haven't yet determined which
wiring (power line to the furnace, thermostat cables, etc) is doing
most of the radiating. When I "sniff" the wires with my walkman radio,
everything seems to be hot with the rf interference. There is no
significant change in intensity with split core ferrites (type 31
ferrite) on the thermostat cable. I haven't yet tried an EMI filter in
series with the ac line to the furnace. That would require some work
on my part, and I want to give Trane a chance to solve this problem.

Yesterday I questioned the electrician about why the furnace ground is
connected to the gas pipe; I didn't get a logical answer. He said that
is the way it's done on all installations. I pointed out that the gas
pipe is bonded to the electrical ground of the house and water pipes at
its far end about 25 feet from the furnace, providing a dc ground but
not an rf ground. I suspect that the gas pipe may be acting as an
antenna. However, there was no change in interference when the ground
is lifted from the gas pipe. A short ground connection to a ground rod
may provide a better rf ground for the furnace.

The outfit who installed my furnace promised to contact Trane today. I
hope to know more shortly about what solution Trane proposes.

Thanks.

Jack, K1VT


Tony Hwang wrote:
modelman wrote:
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.

Hi,
First you'll have to find out whether the interference is coming thru
the power line or thru the air. It can be cured but needs some expert
knowledge. Maybe Trane has noise suppressor kit of sort? Better check
with them.
Tony, VE6CGX