So, the rain water running off the roof is hitting the case? Gutter.

Put some packing foam a few inches thick on top of the case temporarily (the soft squishy kind).

brickeyee is giving you usable advice, to address the question you asked.
if you chose this option make sure that you remove the foam instead of letting it sit on
the housing for long periods. this eventually will cause
the hosing to rust.

installing gutters is a long term solution.
but in the dead of winter..maybe not doable just now.

central hvac is great, but not everyone has, needs
or wants it.

best of luck.

Hey don't play with this things, I would suggest you to call an expert for the same. Go for a technician nearby.

or you can check out

rileyheatandair.com

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