hvac help again

Yes, all the time because the motor/blower is designed to run faster in the a/c mode to make sure you move enough air across the Cooling Coil which is usually mounted above the furnace . However, you may want to examine the blower wheel to be sure a small piece of debris didnt end up on the blower wheel which will drastically change the sound of the blower ; also, make sure your air filter isnt too plugged as the blowers noise will be affected if theres too much restriction from a dirty air filter. Lastly, check your return air grilles and make sure they are unrestricted and that all of your supply registers are open .. as this too can affect blower noise . Finally, make sure the blower door on the furnace is securely fastened and the door seal is in place and still in good condition otherwise youll get a strong whistling noise around the door cracks . Finally...if you want to.....take a video of the furnace in operation which will give us a sound bite so we can actually hear what you are describing .

Which, specifically, do you wish to ask about?

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Greg

Variable speed ECM motor, or pulse modulated if you will. That is a common problem, and I have not yet found the combination to knock the noise completely out of my radios. Thus far, I have replaced the board in the furnace with the latest version and put snap on ferrite beads on the power and control (thermostat) wires. I am still in the process of getting it narrowed down. I have however lowered the noise level from S-8 fown to S-3/S-4. The noise is spread spectrum from 10mhz to up past 30mhz. CB is close to the center @ 27mhz. I have a couple of customers (also HAM radio operators) that also have issues with X13 motors which are a hybrid. In the case of the X13 motors, there is a noise spike every 18khz which is indicitive of a switching power supply. I have been in close contact with the engineers @ Rheem about the problem and will keep you updated. FWIW, some of the other manufacturers (Carrier, Trane, Lennox) do have RFI/EMI kits available.

Thanks. I'll try to find where rf is getting out, and I'll check frame and possibly put filter on ac input. I have portable devices, I'll try probing around. I have a goodman.

I still have to filter my led light drivers, which I hear on fm broadcast band.

Greg

Wow, my thermostat is definitely radiating. I'll clamp that off.

Greg

Modern systems use variable speed fan and (more importantly) compressor motors to save energy. The motors are run like synchronous AC motors - permanent magnets in the rotor with field coils that switch sequentially pulling the rotor around with them, or three phase AC induction motors.

They call that DC inverter or variable speed AC drive. The semiconductors switch abruptly on or off and that will cause a certain amount of RF noise. The semiconductors have to work that way to be efficient. The frequency of AC power sent to the motor changes with speed.

It would be interesting to know the pitch of the sound you hear. Various switching schemes "chop" the power on and off in different ways.

Generally speaking, an ounce of prevention at the source is worth a ton of elimination at the affected appliance - if the noise is that annoying. My electric range was causing my telephone modem to malfunction - nothing at the modem did anything to eliminate the problem yet a simple inductor capacitor filter on the 50 amp range circuit fixed it. Likewise turning the stereo off would cause the computer to crash - a simple "snubber" across the switch contacts on the stereo fixed it.

Oh the skip is on these days. Very few locals actually. Cb is the only thing a trucker has for communication. No other means is workable. Frs quickly loses contact over hills. I'll never forget, you better slow down. Somebody warning me of deep water on the road.

I finally hooked up my sears road talker ssb, converted to Ham 10 meters. That same noise is there. Something seems wrong, I can't hear any stations. Maybe nobody uses those frequencies. Maybe my radio is off frequency. Doing research.

Greg

The sound only occurs near higher speed. It changes overall pitch, but it's got high richly harmonic trash. I checked low frequency, nothing.

Greg

I think CB is totally useful. Darn shame a few people make noise, and ruin it. As for me, I've been on CB for a lot of years. Not as much, now days. I should have it on, more of the time.

Christopher A. Young Learn more about Jesus

Oh the skip is on these days. Very few locals actually. Cb is the only thing a trucker has for communication. No other means is workable. Frs quickly loses contact over hills. I'll never forget, you better slow down. Somebody warning me of deep water on the road.

Greg

I consider it a possibility of it being very important in a disaster. The only communication may come using solar and wind, water, power.

Greg

My HF HAM rigs all have the MARS mods done to them... Yes, they do CB also... but I try not to transmit with them on the CB freqs unless I have to.... something about 200 watts out of the box.

At least a few people still have CB rigs. It doesn't need a repeater, or phone line to work. So, yes, CB has a good potential for being useful.

Christopher A. Young Learn more about Jesus

I consider it a possibility of it being very important in a disaster. The only communication may come using solar and wind, water, power.

Greg

You might check the integrity of the ground on the sheet metal of the furnace. Then maybe walking around with a portable radio, if you have one, to determine where it is strongest. Switch circuits - try different electrical outlets if that's a possibility. Most of the problems I've seen are caused by RF being generated as a side effect then being re-radiated from the electrical wiring or conducted along the electrical wires. (don't overlook any low voltage thermostat circuit in that respect)

It can be frustrating finding the cure, but at least you already found the cause....

CB = redneck telephone

I threw out a perfectly good one since I haven't used it in over 20 years. You must have a lot of stuff! : ) I'm trying to swap stuff for space to put better stuff!

Bill

In a big emergency, the cell phone probably won't work.

And, the truckers will be a good source of un-government- filtered information.

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I've got all my old s*it...Washington base, Lincoln mobile. K40 and Antron Antennae. All of them jacked up with extra channels. I also have a thousand watt kicker.

A cell phone is a far better choice.

If the apocalypse comes, I won't be concerned with what truckers are doing.

Cell phone system can be shut off by govt, just like they can ground all the planes on sept 11.

Hard to shut up a couple million CB operators.

Christopher A. Young Learn more about Jesus

CB = redneck telephone

Sadly, I have way too much stuff. But, it will be useful some day. The cry of the pack rat bird "useful some day".

Christopher A. Young Learn more about Jesus

I threw out a perfectly good one since I haven't used it in over 20 years. You must have a lot of stuff! : ) I'm trying to swap stuff for space to put better stuff!

Bill

After Katrina, the *ONLY* communications that worked were HAM Radio, and CB. Cell phones were all out for several days, and some areas were out for weeks. Power was out for as long as 4 - 5 weeks. I lost commercial power for

Personally, I have a whole house generator, so I wasn't lights out for but just a couple of minutes. I didn't lose any antennas, so I was on the air almost continuously when I was at the house. Second day after the storm, I was at the TV station passing message traffic for them. When I was on the road and stopped anywhere, I was passing message traffic for folks with the rigs in the truck.

BTW... almost *EVERY* fridge/freezer that was lost was due to running on generator and they let the generator run out of gas, or they shut down the generator when the fridge/freezer was plugged in and running.