Your Thermostat is a conventional thermostat and looking closely I see they wired the Auxiliary Heat to the Emergency Heat. Additionally, your thermostat is not fully heat pump smart. Notice the brass jumper between Y and W1.
Let’s talk about Emergency Heat when using a Heat Pump system. The concept is that when a heat pump system fails, the homeowner can activate emergency heat to stay warm until the repair company can arrive and fix the Heat Pump. Now let us talk about Auxiliary Heat. The auxiliary heat is a set of heat strips that are in the air handler and the heat pump will do a couple of things. Specifically when the heat pump ice is up on the outside unit its defrost control board changes the outdoor unit into an air conditioner briefly, do use warm air to circulate through the coil in melt the ice. That means it’s putting cold air back in the house which is not good. So what the heat pump will do as it will activate the auxiliary heat.
Now, in addition to that, a smart thermostat like the nest thermostat, can monitor the heat pumps performance, and on those very cold nights when it’s hard for the heat pump to you keep it up, the thermostat can also activate the auxiliary heat to boost the heat capability on those very cold winter nights.
Only the Nest Learning Thermostat 3rd Generation has the ability to support Auxiliary Heat and Emergency Heat. however, you do not have a separate wire for your Emergency Heat. Your control wires are:
R - Red Wire - Power In 24Vac
C - Black Wire - Power Common 24Vac
G - Green Wire - Blower Fan Relay
Y and W1 - Blue Wire - Compressor Relay
W2 and E - Yellow Wire - Auxiliary Heat Relay
O - White Wire - Heat Pump Change Over Valve
Your wires for the Nest Learning Thermostat 3rd Generation will be:
Remember, you do not have a separate wire for Emergency Heat.
I hope this helps you, and remember ask any questions for clarification.
AC Cooling Wizard
