knocking sound 3 min. after shutdown.NEW by: Wishin I had a Trane
I have a 2006 Rheem 3 ton split heat pump. Last fall I started to notice a Knocking sound occasionally after shut down. Now in cooling it happens after every cycle. I tryed just the blower and it doesn't happen. It's coming from the condensor and traveling on the lineset. Here's what I found so far: the unit cycles off, the indoor fan runs and additional 90 seconds, then within 60 seconds I hear a fast knocking sound that slowly deminishes in speed and volume.The duration is about 10 - 15 seconds. I haven't checked r22 pressures. superheat or subcool yet.
It is a scroll but, I'm thinking check valve in outdoor txv. Anyone ever heard of these symptoms?
Apr 20, 2012 Rating
knocking sound 3 min. after shutdown.NEW by: Wishin I had a Trane
I have a 2006 Rheem 3 ton split heat pump. Last fall I started to notice a Knocking sound occasionally after shut down. Now in cooling it happens after every cycle. I tryed just the blower and it doesn't happen. It's coming from the condensor and traveling on the lineset. Here's what I found so far: the unit cycles off, the indoor fan runs and additional 90 seconds, then within 60 seconds I hear a fast knocking sound that slowly deminishes in speed and volume.The duration is about 10 - 15 seconds. I haven't checked r22 pressures. superheat or subcool yet.
It is a scroll but, I'm thinking check valve in outdoor txv. Anyone ever heard of these symptoms?
Mar 24, 2012 Rating
god awful pounding in a/c by: Dotty
My a/c is 21yrs. old. Even when the a/c is off I get this loud pounding in the walls and attic when the temperature changes from hot to cold. This happens even in winter. The new thing is a rumble of air rushes through the a/c vents. If I didn't know better I swear the house is haunted. Please Help.
Feb 23, 2012 Rating
Both noises by: Anthony in VA
Hey fellas,
This is in response to both noises (loud shut down & blower noise like hitting the wall). Seems like all these problems are with fairly new to not that old equipment. Chances are they are all scroll compressors using r-410a refrigerant(high pressure refrigerant).
It is known in the industry that on shut sown sometimes scroll compressors are noisy due to pressure equalization(this would make the knocking rattle sound). Sometimes it will make the metal noise which may be noise coming from the compressor plates (found in scroll compressors.
This noise is not supposed to happen, but it does with the occasional system. Other factors may be involved. Maybe it was a system replacement and they re-used the old line-set which was not exactly the right size, or too long. I have some units running perfectly for years with the noise.
The air handler noise bang on the wall on start up. Is this a variable speed fan coil? If yes, thats probably what you hear. On start up those motors start by rotating back and forth to find the right frequency before they ramp up speed.
If you hear that excessively the DC hub may be starting to go bad. If it is not variable speed and a psc motor, you may want to check to see if the blower wheel (squirrel cage) is in good shape. good luck!
Feb 03, 2012 Rating
air blower hitting sound by: Anonymous
Our heating unit is about 6 yrs old. Whenever it starts to work, the motor seems starting nicely, however, I would hear the air blower has this delayed response, then feels like something hitting the wall, for about 40 times. The hitting sound will go away after that. It seems worse when it starts from real cold temp and the hitting times shorten when temp is closer. Does anyone know why this is happening?
Jan 25, 2012 Rating
I have the same problem by: Anonymous
I have the same problem.When A/C or heat pume turns off, I can hear a fairly loud slamming noise in the house. like "Peng,Peng, Peng,..."It lasts about 5-20s. It sounds like a metal flap slamming shut, some way like the noise comes frome water tube.
Oct 17, 2011 Rating
Slamming noise with subsequent rattle by: Anonymous
We have the same "slamming" shut off noise problem followed by a rattle on one of the two Carrier model 24ACA air conditioning units that we installed in 2007 to cool our three story townhouse in Houston, TX.
I don't remember them making that much noise at first. They cool nicely but it has become difficult to work in the room located closest to the central air units because of the jarring noise.
We have had them serviced several times without much improvement and have replaced the compressor on one unit with no significant change. Is it also probable that the vibrations from the "slamming" is causing the central ac unit to rattle more as the problem continues?
Jul 18, 2011 Rating
Indoor Fan Abrupt Sound by: Dadan
I'm not 100 percent sure where the abrupt sound came from. It could be within the motor or a sound that is surrounding the motor. The sound could be cause by the motor force air.
You could check you duct system or even you filter. You could also make sure nothing is blocking the air flow.
You could also look at the indoor unit and ask someone to turn ON and OFF the indoor fan (without touching the indoor unit).
I hope the info help
Dadan
Jul 18, 2011 Rating
INSIDE UNIT NOISE by: Anonymous
I have a new outside/inside a/c unit, I am hearing the abrupt stop noise inside. When I called the folks who put the new unit in they said it was probably the blower in the furnace which was not replaced and is not under warranty (GRRRR).
I don't know if it is a problem or just a noise, only hear it when the unit cuts off and I hear it on the inside, any thoughts
Jul 15, 2011 Rating
Me two by: Anonymous
My Heil 5000 condensing unit when it shuts down makes a mid pitch metallic sound like the fan has hit the cage but it doesn't and just spins down normally. It's coming from somewhere else but I can't figure it out. Could it be the contactors?
Jul 14, 2011 Rating
same issue by: Anonymous
I have the same sound and think it has always been there. when starting, it sounds fine. but when shutting down, it's like a loud abrupt stop.
Jul 06, 2011 Rating
Metallic sound at Shutdown by: Anonymous
Mee too.a Heil 5000
Jun 04, 2011 Rating
Exact same noise from 2yr old unit by: Kathleen
Our 3 yr old Rheem makes the exact same noise only when the compressor shuts down. The unit cools nicely and is very energy efficient (great for living in South Florida), but it makes a lot of noise outside when shutting down. It's a loud clunking sound. It wasn't doing this the first year we used it.
Apr 26, 2011 Rating
Compressor sound by: Dadan
I understand once the central ac shut down, the compressor tries to equalize the pressure between the low and high side. In Heat Pump, it sounds somewhat like "Hissss" as it tries to equalize.
I'm guessing from your information. As the compressor shut down, the compressor piston in motion stops abruptly due to high pressure within the copper line.
The refrigerant pressure is great than the in motion piston to rotates. So, as the power cut from the compressor. It take within or less than a second to stop, due to the high pressure. Shawn, does this happen regularly, or it happen at specific outdoor temperature? As it stops abruptly, does it shake the condenser unit? I’m trying to see the big picture.
If my information is correct, there is reason why your central ac unit has higher pressure than normal. There could be airflow restriction across the evaporator coil (dirty filter), condenser coil needs to be clean or I’m just bark at the wrong tree.
I’m not sure what to tell you guys. I will pay close attention to different types of compressor sound next time.
Dadan
Apr 26, 2011 Rating
Same here by: Different Shawn
I have two four year old four ton units. Both central ac units seem to run fine and cool very well. When new they shut down/turned off without any unusual noise. Now they both have a clunking sound or as Ryan said a seizing sound.
To me it seems as if the compressors shuts down abruptly/instantly when power is cut instead of may be one or two more revolutions of the compressor as it slows to a stop.
Apr 14, 2011 Rating
Slamming Sound by: Shawn
Hey, Ryan.
If a compressor made a metallic noise, I doubt it would cool your house. Is this a Heat Pump unit or just regular central ac unit?
You could look around your compressor and checks for copper to metal object contact. If a vibration producing this metallic noise, you should hear when the compressor start.
I'm not sure if a spring form the bottom of the compressor with vibration is producing this sound.
Apr 14, 2011 Rating
I have same problem by: Ryan
Our outdoor a/c compressor unit runs fine.... same as always... cooling is excellent, but from the first day of use this year it makes a loud, short, sharp, metallic noise right as it shuts off.
It's not exactly like metal slamming something, but more like a seizing sound.
At first I thought it was the fan motor seizing on shutoff and the metallic noise was vibration from the fan blades coming to a sudden stop.
But upon inspection the fan keeps spinning freely as it should and the noise is definitely coming from the compressor.
