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Old 06-06-2013, 08:10 PM   #1
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Ruminations on quieting the Dometic Penguin

When I bought my trailer, I lived in Colorado and rarely used the roof air. When I did, it was loud and obnoxious but did its job and shut off soon enough. Since we have moved to south Texas, the roof air is on pretty much constantly during the day to try and keep up and
the sound is driving me NUTS!


OK, there is the woosh of the air which I believe to be largely unavoidable without reengineering the entire lower unit. But my unit has something else: a whistle (or whine).

I would call it a resonance. It is louder and clearer in some parts of the trailer than others, but can be heard everywhere. The pitch changes with the fan speed. It's louder on the LOW fan speed.

Feeling inspired to try to identify this problem, I found an iPad app that gives you a frequency spectrogram to aid me in my hunt.

I have removed the lower plenum to gain more direct access to the airflow.
The high speed frequency is approximately 1300 Hz with the low speed frequency at about 1200 Hz. The frequency spike remains consistent throughout the trailer but does indeed vary in volume.

I have tried some stick on insulation inside the fan housing, with no change in pitch.

This leads me to my next thought: perhaps the fan itself is restricted? I ask this because when you cover the fan output the pitch increases in frequency.



Next Steps:

I'm looking for some kind of sound deadening material that would work on a specific range of frequency

I'm looking for ideas on how to reduce the restriction. There is a black access panel into that part of the plenum but I have not tried to open it.

I welcome the input. If I make any progress, I'll post it here.
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Chris and Christina- Boerne, TX / Evergreen, CO - TAC TX-7
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Old 06-06-2013, 08:15 PM   #2
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There is a fan outside and another fan inside the AC unit. Bugs can get to the outside fan. Dirt daubing wasps can build nest that make the fan run out of balance and when the nest break up could restrict air flow. You can remove 4 screws to remove the shroud, to look at and clean the fan.
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Old 06-06-2013, 08:40 PM   #3
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Thanks. I haven't inspected the outer fan before but I haven been inside and haven't seen a problem with nest of bugs yet. I'll use it as a good chance to clean the coils.
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Old 06-08-2013, 11:40 PM   #4
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Please try to take some photos of the outside shroud removed to show us how the AC is laid out up there.

Kelvin
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Old 06-17-2013, 05:44 PM   #5
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While doing some work on the unit this afternoon, I had taken off the lower bracket and the metal collar from the output side of the AC and the irritating pitch is GONE.

I'm not going to spend more time worrying about the sound on this unit as I am in the process of replacing it with a 15K unit, but you can bet I will do EVERYTHING I can to silence the new unit once it is installed.
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