Dometic roof top shaking

[Steve N Sal]

From time to time both a/c units seem to shake and shutter. I've taken off the shrouds checked to make sure everything is tight and it all seems good. I can turn them off for a minute and turn them back on and then all is normal. ????? This doesn't happen all the time and it doesn't matter if they are in cooling mode or just having the fan on. It almost seems like something might be out of balance but in spinning the shafts and as mentioned checking for tightness all seems to be OK. Any idea what may be causing this?? I should mention these are the Penquin Dometic Duo Therm low profile units.

[MSHappyCampers]

The first thing I would check would be for mud dauber nests on the squirrel cage fan blades. I had that happen on mine.

Also, the rubber bushings that the fan motor mounting screws go through were badly worn on mine allowing excess movement. I bought two repair kits from Dometic (about $6 each) and replaced them myself.

These two things corrected my noise in both A/C's.

[bartlettj]

Will the shuddering stop if you just stop and then restart one of them? I suspect that since you have two you are getting a sympathetic vibration set up after a period of time. Maybe some damping material and/or improving the balance of the fans will help.