Some very good points here and one that was overlooked.
As Herman stated, dedicated lines do not mean isolated or filtered lines. Everything in your house ties back into the breaker box, so it would not be unusual for noise to find its' way from one circuit into another. This is not to mention that dedicated lines do nothing to keep out "sludge" that was already present on the lines feeding your house.
As Gs stated, many electricians will "share" the neutral wire with other circuits and this is not a good thing. Since AC is traveling on both the "hot" and the "neutral", having "half" the circuit dedicated with the other half "shared" doesn't make much sense.
Albert stated that filtering other devices in the house will cut down on the amount of "crosstalk" between noisy devices feeding from outside circuits without detriment to you dedicated lines. This too is a very valid valid approach to noise reduction.
Several others mentioned loose connections at the breaker box, ground system, the central air unit itself, etc... These too should all be checked out. It is good practice to clean the connection at the ground rod every once in a while and this may be your perfect opportunity to do so. Personally, i would kill the mains of the house before attempting to do this though. You might be surprised how many electronic components "leak" voltage from the device to ground, even when not turned on. You don't want your body acting as the conductor bridging the electrical gap between the ground wire and the ground rod as you separate the two.
The part that was overlooked ( from what i can tell ) is that it's quite possible that one of the components that you recently "upgraded" to may not have proper filtering in the power supply. Can you think back to when you first noticed the compressor / fan problem and if you had just swapped some components or cabling in the system ? It's possible that there's nothing wrong with your central air unit and that the problem itself is a poorly designed component.
The reason that i bring this up is that i went through something similar quite a while back. At the time, i was using several different PLC's in various systems. I swapped a PLC ( Brand A ) into a system where i was previously using a different ( Brand M ) PLC. After doing so, i noticed that i was now hearing the noise generated by the arc of a lightswitch coming through this system whereas i had never heard or noticed it before. Re-installing the Brand M PLC into the system solved the problem. Obviously, not all PLC's are as effective as we would like to think. As such, it would only be logical that some components aren't as well designed / filtered as others too. Does this make sense and is the appearance of the noise and the replacement of a piece of gear more than a coincidence ? Sean
>
As Herman stated, dedicated lines do not mean isolated or filtered lines. Everything in your house ties back into the breaker box, so it would not be unusual for noise to find its' way from one circuit into another. This is not to mention that dedicated lines do nothing to keep out "sludge" that was already present on the lines feeding your house.
As Gs stated, many electricians will "share" the neutral wire with other circuits and this is not a good thing. Since AC is traveling on both the "hot" and the "neutral", having "half" the circuit dedicated with the other half "shared" doesn't make much sense.
Albert stated that filtering other devices in the house will cut down on the amount of "crosstalk" between noisy devices feeding from outside circuits without detriment to you dedicated lines. This too is a very valid valid approach to noise reduction.
Several others mentioned loose connections at the breaker box, ground system, the central air unit itself, etc... These too should all be checked out. It is good practice to clean the connection at the ground rod every once in a while and this may be your perfect opportunity to do so. Personally, i would kill the mains of the house before attempting to do this though. You might be surprised how many electronic components "leak" voltage from the device to ground, even when not turned on. You don't want your body acting as the conductor bridging the electrical gap between the ground wire and the ground rod as you separate the two.
The part that was overlooked ( from what i can tell ) is that it's quite possible that one of the components that you recently "upgraded" to may not have proper filtering in the power supply. Can you think back to when you first noticed the compressor / fan problem and if you had just swapped some components or cabling in the system ? It's possible that there's nothing wrong with your central air unit and that the problem itself is a poorly designed component.
The reason that i bring this up is that i went through something similar quite a while back. At the time, i was using several different PLC's in various systems. I swapped a PLC ( Brand A ) into a system where i was previously using a different ( Brand M ) PLC. After doing so, i noticed that i was now hearing the noise generated by the arc of a lightswitch coming through this system whereas i had never heard or noticed it before. Re-installing the Brand M PLC into the system solved the problem. Obviously, not all PLC's are as effective as we would like to think. As such, it would only be logical that some components aren't as well designed / filtered as others too. Does this make sense and is the appearance of the noise and the replacement of a piece of gear more than a coincidence ? Sean
>