Noisy air conditioner when cycling off

In the last week our air conditioner makes a "clunk" noise when cycling off.* Would there be any thoughts on what it could be?

Mine makes a "clunk" sound too- would love to know what exactly is clunking around! To me, it always sounded like the water pump was shutting down and a valve or something closing but that is just a guess. It's only my aft unit that does it too- not the forward unit, though both units are only about 2 years old?

Most compressors are mounted on rubber feet. Most of the time what happens is when it shuts off it torques off to one side and bumps the evaporator or condenser tubing. some times you can gently pry the tubing away or You can usually put a piece of foam between the compressor and what ever it is bumping.

Actually Guys...

That clunking is internal to the compressor...The motor inside actually clunks against the shell of the compressor when the torque is released...

It also usually means that you are running Higher than normal Head pressure (High side pressure) due to either reduced seawater flow, or a dirty (scaled up) seawater condenser...The motor is really under a lot more torque/stress (also draws a lot more amperage) when the head pressure is higher than normal...Hotter seawater this time of year compounds this...

Restoring water flow, and or acid flushing the condenser coil should solve the clunking...

It will also save wear & tear on the compressor, and reduce amperage draw helping your shore cord or generator...

*

Steve~

Marine-AC.com*

I have only seen the "clunk on cycle off problem" twice. Both times it was an all in one unit (compressor, evaporator, condenser and blower in one package.) The first the compressor was mounted less that 1/8 inch from the blower. I loosened the mounting bolts and rotated the unit away from the blower and re-tightened them. The second time I saw it was another unit that had been removed and reinstalled, apparently when they put it back in they bent the mount for the condenser coils, again, almost touching the compressor. I fixed the mount and they had no more problems with the unit. My experience with high head pressure is that a lack of cooling or the unit shutting down from the thermal over load would be noticed first.

Jim Spence wrote:
I have only seen the "clunk on cycle off problem" twice. Both times it was an all in one unit (compressor, evaporator, condenser and blower in one package.) The first the compressor was mounted less that 1/8 inch from the blower. I loosened the mounting bolts and rotated the unit away from the blower and re-tightened them. The second time I saw it was another unit that had been removed and reinstalled, apparently when they put it back in they bent the mount for the condenser coils, again, almost touching the compressor. I fixed the mount and they had no more problems with the unit. My experience with high head pressure is that a lack of cooling or the unit shutting down from the thermal over load would be noticed first.

Click to expand...

*That's Cool Jim * * Wasn't trying to challange you...But this is all I have done for a living for well over 20 years, and with all respect & fairness to you...I may have seen just a few more systems than most...It is a common issue...

Heck...My refrigerator clunks at home on shut off if it gets too much pet hair sucked up in it's air cooled condenser... *

If you have a piston compressor in your unit...Take your hand (with it not running) and shake it around a bit...Bet you hear the same clunking...(don't worry it won't hurt it)

Rotary compressors of today in self contained units are less prone to make the clunk (because of internal construction) when compared to the piston compressors of Split systems, or older self contained units....

Though they are a dying breed...There are still many Piston type compressors out there in self contained units...And just this year we starting to get away from piston compressors in the 16K and smaller split systems that run the new "Green" 410a refrigerant...

Here's an article I wrote, and later edited, about refrigerants & compressors that can explain more:

http://marine-ac.com/2010/01/27/marine-ac-new-refrigerant-regulations/

*

Steve~


-- Edited by spcoolin on Tuesday 14th of June 2011 08:58:01 AM

I came up in automotive A/C so I'm sure you have seen more marine A/C units than I have. One of the reasons that I posted what I did is because almost any one can do the fix that I talked about. Few of us have the meters, gauge sets, vacuum pumps and freon to do more extensive repairs. I always carry all my A/C repair stuff including a 30 pounder of R22 on the boat.

Your article is really interesting and well put together. It looks like they are doing the same thing with R417 and R-22 that they did with R12 and R134. ie It's not as efficient but it's better for the atmosphere. And of course later we found that wasn't exactly true either. Thanks for the info.

Jim Spence wrote:
I came up in automotive A/C so I'm sure you have seen more marine A/C units than I have. One of the reasons that I posted what I did is because almost any one can do the fix that I talked about. Few of us have the meters, gauge sets, vacuum pumps and freon to do more extensive repairs. I always carry all my A/C repair stuff including a 30 pounder of R22 on the boat.

Your article is really interesting and well put together. It looks like they are doing the same thing with R417 and R-22 that they did with R12 and R134. ie It's not as efficient but it's better for the atmosphere. And of course later we found that wasn't exactly true either. Thanks for the info.

Click to expand...

*Well...417a is a blend...Where R-134a is not, and was developed to simulate R-12 operation...417a is forulated as a Drop-In replacement for R-22 in existing systems.

I also have a Drop-In (blend) on the truck for R-12...Have to go out & look (don't use it much) but I think it's R-416a...It works pretty well for everything except low temp applications (like -10* evaporators)

Thanks for the Kudos on the article...

For everyone else that does not have gauges...A good way to tell if your unit is running high head pressures and may need flushing....Feel the water coil...The top run should be hot...But the bottom run should not...

Hot Bottom...Better Get Er Washed *

Steve~


-- Edited by spcoolin on Tuesday 14th of June 2011 12:32:10 PM