Geo-thermal Heat Pumps, Ground-source Heat Pumps
"Do not let the outdoor unit sit underneath a leaking gutter.
In the winter months, water will drip on the top of the unit and freeze solid.
This will restrict the air flow and cause the whole unit to freeze-up. "
I had rain water dripping down the east wall of my house. It would work it's way
down and splash around the air intake.
I've sealed off that water entry point and hope to see less icing now.