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slickwilliam 05-19-2012 08:45 PM

Vibration in refrigerant supply line
About three months ago, we had a builder's grade Goodman updraft furnace replaced with a high-efficiency Carrier unit. The furnace is in the attic, with two return ducts entering at the base of the unit, and a cooling coil at the top, followed by a plenum and the distribution air ducts.

During replacement, the techs suspended the evaporator/ducts assy from the roof rafters while they replaced the furnace.

Today, I happened to touch the high-pressure line and noticed what felt like "slugs" of refrigerant flowing through the line. The sensation is similar to holding the line in one hand and banging it lightly with your knuckles a couple feet away. Not having paid much attention to the line before, I would expect the refrigerant flow to be smooth, not pulsating.

I have a feeling we're low on refrigerant, possibly from a leak caused by flexing of the lines/connections/joints during furnace replacement.

Does this sound like a reasonable diagnosis? If so, I doubt whether we could get the install guys to fix it since it could just be coincidence... :whistling2: Just wanted to know if I was probably right...


gregzoll 05-19-2012 09:00 PM

If you did not feel the liquid movement or hear the hum, then yes there would be a problem with your system. My guess is that you have a heat pump, not a standard air conditioner.

Doc Holliday 05-19-2012 10:15 PM

It sounds like a thermostatic expansion valve doing it's job.

slickwilliam 05-20-2012 03:25 PM

Thanks for your replies. It is not a heat-pump (hence the furnace replacement) and I would expect an expansion valve to operate more smoothly.

Well, we'll just keep an eye on it and see what happens. It's working right now, so there's no urgency. (That'll likely change when it finally breaks entirely in August... :laughing: )

Again, thanks...

Doc Holliday 05-20-2012 03:44 PM

An expansion valve when closed makes for a higher pressure. When it opens the pressure releases on the refrigerant in the high side line. It is always opening and closing, you can see it on refrigerant gauges.

Anyway, that's just one possible suspect. I've come across the lines vibrating when the condenser was blocked resulting in extremely high head pressure.

It also could be that you have a kink in the lineset somewhere. All I can do is speculate from here.

Marty S. 05-20-2012 04:53 PM

Also could be low on charge due to a leak as you suspected. Once it's low enough to lose subcooled liquid in the line no longer stays in a liquid state the whole way to the metering device. Sounds and feels like air bubbles in the line since the refrigerant is changing from liquid to a vapor.

slickwilliam 05-20-2012 09:37 PM

Thanks, Doc. I would expect an expansion valve to be much more of a gradual change and temps/pressures gradually built-up or changed in the system. These are pretty sharp pulses, happening once or twice a second.

Marty, I think you may be correct. It does indeed feel like flow turbulence in the line, much like a garden hose that has some air bubbles in it when first turned on. And the low refrigerant seems like a reasonable guess as the furnace install crew pretty-well manhandled the coil/plenum assembly when they replaced the furnace beneath it. It wouldn't surprise me to find a hairline crack in one on the lines' solder joints. Or the line itself for that matter. I think I'll have them come out and check refrigerant levels...

Again, thanks all for your replies, and have a great evening...


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