Kimmie, about the emergency heat switch:
A heat pump moves heat from one place to another. In fact, if you turned a window A/C around in the window, it would heat the room, even in the winter. A heat pump does the same thing with a reversing valve.
However, once the outside temperature drops below a certain point, there is not enough heat energy in the air to support the freon evaporation outside, and the heat pump can no longer keep up with the demand for heat.
At this point, typically when there is a 2 to 3 degree difference bewteen the desired and actual temperatures, the unit brings on a supplementary heat system, electric strip heaters in an all-electric house and in many other houses.
You can also engage this auxiallary heat manually with the emergency (or aux) switch. The compressor may or may not shut off at this point, because it still contributes a little heat, but the efficiency plummets drastically.
I'm lucky in that my house has gas, and the backup heat system is a gas furnace. While most people hate to see that little light, which means large electric bills, we're comfy in using the gas furnace on purpose, and not running the compressor at all.
