I have a goodman GSZ130241AB heatpump. The house is brand new, and this is the first winter for us. I've noticed now that its dipped to close to 0 degrees C, the thermostat will show 'aux heat on', and the house will heat but the actual heat pump unit outside will be off. As soon as the temperature outside goes up a little bit, the heat pump functions as normal -- the outside unit runs, thermostat just shows that it is heating.

My understanding is that the heat pump should *also* run at this temp. I don't have and couldn't find an owners manual or similar on goodman's site though.