AC Air Box Replacement

[rgarner]

I just replaced the AC ceiling air box cover on my Sunseeker 3100 that provides the directional vents for the Dometic Brisk Air AC. I did not replace any controls or any part of the actual metal housing....only the plactic cover (the vents on the old one were broken and 'whistling). You'd think there would not be an issue, as I simply unscrewed one and screwed the new one in. However, now the A/C unit seems to have a significant vibration. My guess is that it is the 'squirrel cage,' as it starts as soon as the fan (without AC) comes on and is worse at low speed (it is slightly better on high). Anyone have any expereince with this type of issue or have any suggestions? Thanks!
Post Script-the A/C ran all last night and 'something' happened as the vibration is much less this morning....curious.

[BigJohnD]

Mine has a vibration as well. Been like that since i bought it. Sometimes a dirt dobber nest on the condenser fan blade will do it, but ours never stays outside unless we're camping, then the ac is running non stop. In our case, either the motor / fan shaft is a shade off or the fan itself is out of balance. I went up there while it was running and its obvious something is out of whack.

[rgarner]

Well I have not tried this yet; however an AC guy--who's been in the business for a long while---says that the squirrel cage is likely out of balance. He recommends releasing the set screw that holds the cage on the shaft, place the fan on low and let it find the sweet spot on the shaft---operating in balance----and then lock it in place there.