Roof A/C Vibration

[Mariner]

Just had the fan motor replaced in my rear Dometic roof A/C. Now when we turn it on it makes a gawdawful noise and vibration when the compressor kicks in, that there's no way you can sleep in the bedroom.. What would a fan motor replacement have to do with that?

[Jim & Wilma]

The fan motor drives both the condenser and evaporator fans and one of those is unbalanced; probably the condenser fan as it's an axial fan and one of the blades could have bent. We once had a small mud dobber nest built one one of the blades and you'd have thought the A/C unit was going to rip itself apart.

 

Suggest you try running in Fan mode to verify it's just the fan. If so, should be an easy fix.

[Retiredin1993]

The fan could have gotten cracked when it was installed.

[Kirk W]

.. What would a fan motor replacement have to do with that?

Nothing at all, if the blower was installed properly but those units are pretty compact so it may be that the tech had to do something effecting the compressor in the process. Each of them use a separate motor, so they should not effect each other but it might be that the separation was changed and somehow vibrations are being transmitted between the two. If it were me, I'd start by going up on the roof and removing the shroud and then have someone turn on the a/c to watch what is happening. I'd do that just to see if I could tell what the problem is, but since you say the work was just completed, the tech or shop that did the work should correct it for you. If I were the tech, I would want to know of the problem.

[Bill Joyce]

Yes, those blower motors can come unbalanced or get damaged in shipment. We once had to wait three weeks for a new one when ours arrived damaged. The damaged one behaved just like you reported. It took three weeks because the place ordering was not Dometic authorized and had to work with someone who was to get parts. If we had only known they were not authorized!