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[JeffVolp]

I tried installing a pair of 20A filters on the mains going to the HVAC and it did not help.  I planned at one point to replace that with a single XPF at the circuit board power.  In the end, I don't have it filtered at all since fixing everything else made enough improvements that the HVAC was no longer required.

If the problem only occurs when the HVAC blower is running, filtering that line should help.  You don't have to filter the 240V line that feeds the A/C compressor, only the circuit that feeds the electronic control unit for the furnace and blower.  Be sure you have a good connection from the XPF white lead to neutral to provide a low-impedance path for the noise.

Jeff

[Garybuy]

the new furnace does not have a variable speed fan -- single speed only.  What's your suggestion -- the issue seems to be more prevalent when the AC unit is on.  Should I install at the unit or in the circuit breaker box?

[bkenobi]

The XPF is a 20A module.  Most (all?) central A/C units are rated higher than 20A.  If you install at the panel, you will not be able to use a single XPF as it is not rated for the load and will fail (which could be dangerous, I'm no electrician).  Jeff provided a schematic that should share the load across 2 XPF modules to allow for up to 40A load but it did not seem to help me.  However, as Jeff posted above, I may have had issues with my installation such as solid connection to neutral.  I used wire nuts to tie 3 lines together but a better option would have been to solder the 2 XPF leads to a 3rd wire and wire nut that to the panel.

If you have access to the load that's actually causing the noise in the A/C, it would probably be better to do that since it will simplify the setup.  In my case, I believe I would have had to either splice wires on my new HVAC system or source connectors to match what it uses and build a pigtail.  I didn't want to void the warranty so I tried 2x XPF at the panel.

[JeffVolp]

What's your suggestion -- the issue seems to be more prevalent when the AC unit is on.  Should I install at the unit or in the circuit breaker box?

All the HVAC compressors I am familiar with have an induction motor with a phase-shift capacitor.  Nothing in the compressor would be generating noise, and the relatively high inductance of the winding should limit its loading.  So I don't think filtering the high-current line would have much effect.  Of course, it is possible that your signal levels are low to begin with, and adding the high current draw lowers the signal enough that it becomes marginal.  If that is the case, you may have better results boosting signal levels than trying to filter the A/C unit.

If you have a separate control circuit powered by 120V like we have at our home, you might try filtering power to that unit.  It might have a switching power supply that would generate noise.  If so, it could generate more noise when driving the relay that turns on the A/C compressor.

Unfortunately, without some sort of signal meter, troubleshooting an X10 system can be a trial and error process.

Regarding the XPF filters, what I meant by a solid connection was a direct path to the neutral/ground buss in the panel.  Wire nuts should be fine.  The closer it is to the buss, the better the attenuation because it reduces the inductance in that run.

Jeff

[bkenobi]

Regarding the XPF filters, what I meant by a solid connection was a direct path to the neutral/ground buss in the panel.  Wire nuts should be fine.  The closer it is to the buss, the better the attenuation because it reduces the inductance in that run.

Oh, ok.  I pulled the setup off the panel since it didn't seem to help.  But, from memory I ran a 4 conductor wire from the panel to a box next to it with the 2 XPF modules located within.  I ran Power, Neutral, and Ground from the panel to the XPF and connected with wire nuts.  I ran the 4th conductor back to the panel from the load side of the XPF.  I used a wire nut in the panel to connect the returning Load wire to the HVAC controller line.  The HVAC worked correctly both with/without the XPF but I saw no measurable improvement in signal strength/degradation/noise with the meter under any HVAC run condition.  I saw no ill effects from the installation so I believe the 2x XPF setup was working as you described it just was not improving the issue I was seeing.  Had I continued to see issues, I would have added a single XPF to the HVAC and had my contractor install the unit on the HVAC controller to avoid warranty issues.