Heat pumps are created to run in cold weather and have provisions to deal with the liquid.

Crank case heaters are one option, they are a low wattage heater that keep the compressor warmer than the interior coil during the off cycle, preventing the refrigerant from migrating to the compressor.

Some straight A/C units have these and you may see a little warning sticker telling you not to run the compressor for 12 or 24 hours once power has been restored.

This is designed to give the low wattage heater a chance to heat up sufficiently to drive the liquid refrigerant out of the compressor to prevent start-up damage.

A more common method is a suction line accumulator and as has been mentioned and the scroll compressor.

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Jim Luttrall
Mr. Inspector.net, Inc.
Allen, Texas 75002