Hello, thank you for your question.
Manual of the LG LT101CNR Air Conditioner, Page 11:
"If you use an existing wall sleeve, you should
measure its dimensions.
Install the new air conditioner according to these
installation instructions to achieve the best
performance. All wall sleeves used to mount the new
air conditioner must be in good structural condition
and have a rear grille to securely attach the new air
conditioner. (FIG. 1)
With the LG sleeve (optionally supplied with
your unit), you can maintain the best performance of
the new air conditioner. (FIG. 2)"
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