just recently had a new system (compressor and air handler) installed in
my home and now there is a swishing sound coming from the liquid line (small
one). The sound did not occur with my old unit (which was a bit smaller)
and I wouldnt worry about it except for the fact that the lines run above my
daughters ceiling and she is having a hard time sleeping when the a/c comes
on at night. What might be a possible cause and solution for this problem.
The installer said it has to do with refrigerant flashing in the line and
doesnt seem to think there is much that can be done. But as it didnt happen
with my old unit I would think that there is something that can be done.
Thank you for your time!
Refrigerant should NEVER be flashing to gas in the liquid line! That
will greatly reduce the capacity of the system.
Yes, it could be low on refrigerant, or there could be a restriction
'somewhere in the Liquid Line Circuit' causing flashing. I doubt that it
is hot enough, where the liquid line is in your home, to cause flashing.
That problem definitely needs to be corrected, ASAP. Darrell - udarrell
Crank Your Air-Conditioner Up To Specs
Darrell said it right. If your old system was smaller, the liquid line
may be too small for the new larger system. The installer should have
figured that out before he installed the new system. By the way, why
did he install a larger unit? Did he do a load calculation? He may
have oversized the system. There may be a refrigerant leak in the new
system. At any rate, the contractor should come back and take care of
I thank everyone for the responses! I did a little more investigation and
it would seem that the noise is more prominent the closer you get to the
expansion valve. You cannot even hear the noise outside at the compressor.
The air handler is brand new so I wouldnt think that the expansion valve
would be worn out (if they even wear out at all) but is it possible that it
is a faulty expansion valve and is somehow causing the hissing/swishing
sound? He did do calculations and figured that my old unit was too small.
And he also charged the unit using some superheat calculations, pressure and
temperature guages in the house and on the return line. I was standing next
to him the whole time as he explained the process. So I would think that
the unit is charged correctly but maybe I could ask him to come back and
check it just to make sure because you never know! Thanks again for the
input! It is greatly appreciated!
This is Turtle.
The only thing I could say do and maybe do some good is to take a roll of Gum
wrap and insulate the TXV / expanion valve real good and cut the noise level
down a good bit. Take the whole roll to wrap it with and do use real Gum Wrap to
wrap it with and not the spong rubber stuff. You can cut maybe 1/2 the noise out
with this method.
Could be low on refrigerant or something as simple as the line resting on
the rafters causing the sound to carry through the wood beam. in either
case, I would ask the installer to come back out and remedy the
If your AC works perfectly other than the noise, then you need to try
insulating the line noise from your daughters room.
1. Lift it off the joists - if necessary, hang it from the rafters,
but definitely don't let touch any of the framework around her room..
2. Insulate the line over her room with extra insulation.
3. Insulate the ceiling over her room.
Thanks for the input! I wish it were that simple though . The problem is
that the line runs through a vaulted ceiling so that would require me to rip
off the sheetrock. As a last resort I thought that I may have to have the
installer reroute the lines around her room to fix the problem but am hoping
that it wont come to that because it will add 15 to 20 feet to the length of
the lines and i will have to run them down the outside of my house instead
of through the outer wall which doesnt look as good. It must have something
to do with this new unit because before I got this new unit I never heard
this sound in the 8 years that I have lived in the house.
I never heard an Alco expansion valve make that much noise.
BIFLOW valves should be used only on packaged heat pumps.
A combination check/expansion valve would be used on a split system
Undersized liquid line could have velocity noise.
Undercharged system could have noise in the liquid line.
I would not consider a valve that makes lots of noise during normal
operation, "spiffy". And unwanted noise is not lovely.
The Uni Aire unit uses a Alco BI Flow valve to inject a 20% quality
liquid/gas mixture into the liquid line and so do a number of other
manufacturers. For this reason the
liquid line has to be insulated. The standard method of course is check
valves with either TXV, or capillary.
The question asked cannot be answered by anyone as
there a number of possible reasons for the noise from
a partially blocked drier to an undersized liquid line.
HAVE A NICE DAY SAILOR
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