Dometic Cruiseair 10,000 BTU Rockcrusher

ttmott

PhD in OCD
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TECHNICAL Contributor
Apr 3, 2012
7,960
Space Coast Florida
Boat Info
2006 52 Sedan Bridge
Engines
Cummins QSM11
The mid cabin and guest head HVAC system is a Dometic DTU10 10,000 BTU self contained unit and it's very noisy; a loud harsh harmonic vibration with much of the noise coming out of the ductwork. It's a rather new unit on the boat; replaced the original about 2 years ago. This unit does not have the optional compressor noise shield however even without the shield ($290) Dometic states it's an extremely quite unit.... Short of removing the unit and sending it to a watery grave, we have done just about all we can to isolate the noise but simply can't determine other than the fan when running alone is quiet but when the compressor comes on line the insufferable noise ensues.
It's a very common HVAC unit so I thought if anyone else has experienced this situation, what was done to correct?
 
You dont mention specifically, but is the any acoustic foam on the compartment walls, or other mechnical noise suppresion means ie a baffle on the air inlet?
 
You dont mention specifically, but is the any acoustic foam on the compartment walls, or other mechnical noise suppresion means ie a baffle on the air inlet?
It is installed behind the port dinning table seat under the gunnel; so, yes there is quite a bit of "sound insulation".

Was it installed using the rubber vibration reducing mounts?
I looked at this and the drain pan is directly mounted to the fiberglass deck but the compressor has the rubber isolation mounts; it is as originally supplied by the manuf.

FYI - The 25,000 BTU solon unit is installed just aft of this one in the same area and is relatively quiet, in fact, comparatively silent..... The 15,000 BTU forward cabin unit which is under the bed is quiet.... And, the 25,000 BTU unit on the bridge which has no sound insulation is comparatively quiet....
 
Hey Tom, aside from the noise. How well does the unit actually operate/cool? Wondering if it is possible that it is slightly over charged as that will sometimes make compressors noisy.
Actually, I think it's not performing on par to the other units. I should have an AC tech check the refrigerant.
 
Domestic has great customer support. I would suggest giving them a call and talking to a support technician.
 
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Actually, I think it's not performing on par to the other units. I should have an AC tech check the refrigerant.
The smaller the unit, the more important it is that the charge is accurate. This in turn, will not only make the unit function more efficiently but also increase the life expectancy.
 
A little testing yesterday. Pulled the unit out of the boat and ran it on the bench.
  • Compressor and fan running - loud rumbling noise.
  • Compressor running and no fan running - rumbling noise gone.
  • Compressor not running and fan running - rumbling noise gone.
Removed the fan motor and squirrel cage from it's housing and there is a miniscule amount of shaft play (like less than 3 thou) so what we can surmise is there is a harmonic / natural frequency interplay between the fan running, it's shaft play, and the compressor running vibrations. Moving the fan motor shaft back and forth makes a noticeable "bonking" noise through it's mounting plate. there are no bearing issues in the fan unit; very smooth rotation. Hopefully the refrigerant charge will be checked Monday.
Call in to Dometic Monday.....
FanPlay.JPG
 
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The shaft end play of .003 is about normal and will decrease slightly when its warms while running so no concern there. The blower wheel/squirrel cage could be out of balance and many times a weight can be found on replacements.

http://www.balancingweights.com/25-pc-pack/?sort=priceasc

Plenty of vids on youtube of how to balance it.
 

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