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Old 11-24-2019, 01:02 PM   #1
Skippy38
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A/C Rattling Badly...

I have Dometic Brisk Air II 15k unit. I have not run it in a few months and decided to flip it on today. It is putting out a pretty stout vibration but cooling as well as always. I pulled the top cover and the whole compressor/fan/control box unit is vibrating pretty badly, you can feel it vibrate throughout the entire coach. It is only about 3.5 years old, could it be time for a new a/c unit already or can they be repaired?

Thanks.
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Old 11-24-2019, 01:06 PM   #2
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If you removed the ceiling cover, you didn't get a good view of the fan on the roof. the motor runs two separate sides and the side on the roof can only be seen by taking the cover on the roof off.
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Old 11-24-2019, 01:15 PM   #3
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I did remove the cover on the roof, that is how I could see the whole compressor/fan/control box unit vibrating pretty badly.
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Old 11-24-2019, 01:21 PM   #4
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Unbalanced blower wheels are the usual culprit. Maybe take the ceiling plenum off and look at the other fan in the unit.

You mean you took the roof cover off and then the front ducting to see both fan wheels?
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Old 11-24-2019, 01:45 PM   #5
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I did take off the front ducting to look at the blower fan wheel, and can see both fans. There is no damage, bug nests, etc. In fact it looks like new. The entire fan motor assembly is shaking badly. Could it be time for a new fan motor? How difficult is it to change it?
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Old 11-24-2019, 02:03 PM   #6
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It’s easy to change. I would remove the 2 blower cages first and try it.
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Old 11-24-2019, 02:16 PM   #7
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Thanks man. After I got it taken apart and was able to see it run it is obvious that the fan motor has somehow become unbalanced. Looks like I will be replacing it lol. I may even do a youtube video on it...
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Old 11-24-2019, 02:32 PM   #8
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I doubt the fan motor is unbalanced. The fan squirrel cages may have thrown a weight and become unbalanced. I'd check for excessive bearing run out "play in the shaft". Look carefully at the blades of the fans. If a weight has been lost you should see a spot on the fan that markedly cleaner than the rest of the fan.
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Old 11-24-2019, 02:34 PM   #9
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Good point. I will check that possibility on both fans. The entire motor assembly is shaking pretty violently when it is running, but it is cooling as good as ever...
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Old 11-24-2019, 02:39 PM   #10
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Originally Posted by Skippy38 View Post
Good point. I will check that possibility on both fans. The entire motor assembly is shaking pretty violently when it is running, but it is cooling as good as ever...
If you continue to run it out of balance then you will wipe out the bearings in the motor.
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Old 03-05-2020, 07:58 AM   #11
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UPDATE: I ordered a new fan motor on Amazon ($104). When I took out the squirrel cage/motor/fan assembly I noticed a mud wasp nest on the back of the fan that I couldn't see. Cleaned it off and what do you know? No more shaking. However, there is about 1/16" lateral end play in the shaft. Is this normal? Also, 2 of the 4 soft motor attachment screws kind of cross threaded, but the unit is running smoothly.

Since I have the lateral end play should I go ahead and replace the motor anyway? What can I do about the motor attachment screws? It is not shaking at this point...
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Old 03-05-2020, 09:07 AM   #12
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The 1/16" lateral runout might be from those two stripped set screws, or it may be from bearing damage caused by the unseen mud dauber nest. You should be able to buy replacement screws at any "decent" hardware store. Also, there's a "specialty hardware section" at Lowe's. The last time I needed a "strange, never saw one of those before" part, I found it at Lowe's, in a drawer along with 10 or so "spare ones"....
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Old 03-05-2020, 09:42 AM   #13
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The 1/16" lateral runout might be from those two stripped set screws, or it may be from bearing damage caused by the unseen mud dauber nest. You should be able to buy replacement screws at any "decent" hardware store. Also, there's a "specialty hardware section" at Lowe's. The last time I needed a "strange, never saw one of those before" part, I found it at Lowe's, in a drawer along with 10 or so "spare ones"....
Thanks. I just ran it for about an hour and it runs like normal. The set screws are a different story. When I feel underneath them they are flat and have no 'head" on the screw. I think the may be pressed in or integral with the mounting bracket? If so I would have to cut them off and drill them out to replace them...
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