AC fan vibration

hlh1 · 05-12-2023, 12:05 PM

I've heard a minor rumble from the AC fan since I've had this TT. It's not a big deal, but it's there. I hear it with and without the compressor running. I pulled the shroud off the unit and looked the fan and squirrel fan over and can find nothing on either that should cause it to be out of balance. All looks good. I see that the motor fan is rubber mounted, like they expect it to vibrate some, and the motor is vibrating/rumbling a bit. I have checked the AC mounting bolts from the inside, and they're good (not too tight, but tight enough). I guess I'm wanting perfection that's just not going to be found on this Dometic AC. It blows cold air. Am I missing something?

NH_Bulldog · 05-12-2023, 12:29 PM

Mine developed a bit of a vibration issue after a few years. While I was up there with the shroud off installing my soft start last spring, I checked both fan blades and found some dirt build-up on the squirrel cage which I scraped, vacuumed, and wiped down.

On the regular fan blades, I wiped them as well, and also performed a quick alignment check; brace a block of wood against a solid point on the frame and move it close to the blade until it juuuuust barely touches. Then slowly turn the fan and make sure each blade barely touches the block the exact same amount. If one or more are not touching, you could try to give it a slight bend in whatever direction is needed.

Lastly, since the fans are plastic, they would be warped enough to be out of balance.
Fortunately for me, cleaning did the trick and the vibrations went away.

hlh1 · 05-12-2023, 02:11 PM

Rob, I removed and cleaned the blades. All looks good and clean, and it still vibrates a bit. I may look into balancing the blades when I get a chance.

**JRTJH** · 05-12-2023, 04:43 PM

Quote:

Originally Posted by hlh1

Rob, I removed and cleaned the blades. All looks good and clean, and it still vibrates a bit. I may look into balancing the blades when I get a chance.

Just a thought, if you removed the blades to clean them, did you by chance turn on the A/C unit to see if the motor shaft was straight and did not have any vibration? Sometimes, the shaft, the actual armature or the bearings inside the motor can cause even a well balanced blade to vibrate.

bobbecky · 05-12-2023, 07:30 PM

Some years ago, our front A/C started vibrating and after investigating, discovered the plastic blower had broken on the edge of the open end. Looked perfect, but once it was running, the centrifugal force opened up the break and it would rub on the area around the blower wheel. Might be something to check.

jxnbbl · 05-13-2023, 03:04 AM

As others stated, everytime I have something like this happen observing the unit (whatever it is) running with the vibration will reveal the source. something is most likely loose. In some cases, I've found an assembly issue and part A is too close to part B and the vibration happens when the fan runs.

hlh1 · 05-13-2023, 11:48 AM

Quote:

Originally Posted by JRTJH

Just a thought, if you removed the blades to clean them, did you by chance turn on the A/C unit to see if the motor shaft was straight and did not have any vibration? Sometimes, the shaft, the actual armature or the bearings inside the motor can cause even a well balanced blade to vibrate.

I put it all back together and did not think about doing this. I'll have to do it next time I have it apart.

hlh1 · 05-13-2023, 11:50 AM

We're now on the road and I'm pleased that it still works and keeping us cool. I'll have to tear it apart again in a couple of weeks and check out various options.

Rdynbama · 05-19-2023, 05:28 AM

Ours developed a vibration and the rubber washers on the fan motor mounts were not up to their task .I had some rubber gasket material and cut and added more washers and the vibration is gone.

hlh1 · 05-19-2023, 05:43 AM

Quote:

Originally Posted by Rdynbama

Ours developed a vibration and the rubber washers on the fan motor mounts were not up to their task .I had some rubber gasket material and cut and added more washers and the vibration is gone.

Another thing I'll check when I return.

hlh1 · 05-31-2023, 12:38 PM

I pulled the fans off and the motor runs smoothly. The rubber motor mounts seem fine. I washed the squirrel cage fan since I found a lot of pollen/dust stuck on the blades. I then put everything back together and cleaning the cage fan helped some, but I still have some moderate vibration. I'm thinking I should have tried running the motor with each fan separately to isolate which fan may be the worst. I'll try that next.

NH_Bulldog · 05-31-2023, 02:14 PM

Here’s a potential twist…..this past weekend while camping, we were running the fan for circulation before it got hot. It was smooth as can be, no vibration. But later when we switched to AC mode, there was a definite vibration but only while the compressor was running. Not enough to bother me, but the next time I am up there I am going to check the compressor mounts.

hlh1 · 05-31-2023, 04:16 PM

Quote:

Originally Posted by NH_Bulldog

Here’s a potential twist…..this past weekend while camping, we were running the fan for circulation before it got hot. It was smooth as can be, no vibration. But later when we switched to AC mode, there was a definite vibration but only while the compressor was running. Not enough to bother me, but the next time I am up there I am going to check the compressor mounts.

I'm definitely getting the vibration with and without the compressor running. But the compressor does add it's own minor hum to the mix. Like you I often run just the fan for circulation, especially at night where its "white noise" helps us sleep.

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