knocking a/c unit

Question

hello again guys. well I have been working on the a/c once more. I replaced the control box & tstat. it all works but I'm getting a knocking/thumping sound from rear a/c unit.
I have a 96 Alegre bay with dometic dual air units. the sound is coming when the rear unit is on & only from the rear unit. I have pulled the top cover off & bottom cover & checked for any sorts nests & have cleaned everything. the unit seems to be working good but it makes a very loud & steady knocking sound.
I was wondering if these units have a bearing or something that can cause them to get out of balance? the fan spins easily & steady with a tune of the hand. if u know of theservice things getting out of balance or another issue that would cause this , please let me know what I can do to fix it thanks.
just spent $300 to change the tstat & boxes I really don't want to have to replace this unit as well. thanks

mountainair05 · Answer

Did you check the blades for dirtdevil mud nest.  You should be able to check the compressor or motor wit it running by putting your hand on each one. That will tell you which is making the noise.

newman_fulltime · Answer

are the mounting bolts tight? is the base bottom plate cracked at the compressor?

wa8yxm · Answer

DO they have bearnings.. YES. But another issue.. Give me some thought timne

A nest causes not so much knocking as fairly high speed vibration... But anything that causes an imbalance can do it too, but the fan and blower turn fairly fast so it is what I'd call vibration more than a "knock" but then.. You and I may define things differently So I will go with my syspect list.

Inspect the fan for any nicks or breaksm if a piece of a blade has broken off that will do it.. Likewise inspect for CRACKS in the plastic.

Do the same with the blower......

True story:
One Friday in August, early evening, I noticed my across the drive neighbor up on his roof looking at his Carrier Air V. HIs complaint was a RATTLE sound.. He fired it up and I confirmed.. Seemed to be coming from the blower end more than the fan so I showed him how to pull the inner cover (And assisted) he inspected the blower and it was ..... Cracked clear to the hub.

Late Friday. Nearest parts store 30 miles and likely closed even if they have it. nearest parts store likely to have it 100 miles.

I had one in my basement.. He was very happy

rls7201 · Answer

The compressor is mounted on Metalastik mounts inside the hermetic case. I suspect one of the mounts has broken. Richard

b_b_upch · Answer

thanks guys hopefully I can get in there &amp; check these things out today

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knocking a/c unit

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