Outside care of your HVAC unit is as important as inside care, especially in the winter. All the ice and snow we get can have lasting affects well into the spring and summer. Here's how: Ice Build Up on Heat Pumps Not all ice and snow build-up on your HVAC unit is an emergency. Heat pumps operate via a refrigerant that absorbs temperature from the Earth's atmosphere. When the temperature is below freezing, the moisture freezes instantly. This can cause your heat pump to run