Earthtraveler5,
I guess it’s time now for the ugly truth, lol.
Your Goodman heat pump has a reversing valve that when not energized the system is in heating mode. To get AC cooling mode you have to energize the reversing valve on the OB terminal. When your heat pump is in heating mode, the defrost control board temperature sensor closes at 31°F, that is sensing ice on the coil, and that initiates the defrost cycle and the defrost control board then sends a control call on the W2 wire of the outdoor defrost controller to the indoor unit to activate the auxiliary heating, in your case the gas furnace. In systems that do not have gas heat they have the indoor coil and usually 15kW to 45KkW of electric heating strips that are the auxiliary/emergency heat.
You sort of have the best of two worlds, depends if gas or electricity is less expensive per equivalent BTU of heat to heat your house. The problem is a normal thermostat does not have the intelligence to make that decision for you. In the case of the Nest, and most smart thermostats, when it is programmed as controlling a heat pump it can only assume that there is auxiliary and or emergency heating. Furthermore, the thermostat considers the heat pump as the primary mode of heat. As a homeowner you will only be able to get gas heating when you place your thermostat in emergency heat or auxiliary heat mode. Otherwise the heat pump will be your primary motive heat and it will only signal the gas to come on when the outdoor unit enters defrost cycle.
The outdoor unit connection points are only C, Y, R, W2, G. This picture below, from the installation manual, shows the Heat Pump Low Voltage Junction Box.
Now let’s talk about the humidifier, the humidifier has as you understood correctly, two wires one is common and one is control voltage. The humidifier is a self-contained unit that has a humidistat and a setting that the homeowner can place for the desired humidity level during heating periods. The most desired heating percentage is 50% typically. When the control wire is activated it signals to the humidifier to turn on and using the humidistat will measure the humidity and if it’s below the desired level it will activate the humidifier function. We only need to send one wire from the thermostat there and that will be the red wire and the white wire will be connected to the common in the furnace.
The wires you have numbered will need some adjustment, #5 wire will not be used, the #6 (W2) from the furnace and outdoor unit will go to the W2(#5) position in the thermostat. All the other wires, as you deduced are correct.
when you go through the Nest online configuration tool you will list the wires that on your old thermostat are as follows. Rc, C, Y1, W2, O/B, G, HUM.
Ken, The AC Cooling Wizard
Thank you Ken.
My big question is where to connect the W3 / AUX2 wire and the humidifier wires.
According to the doc: Nest Learning Thermostat Pro Installation & Configuration Guide, they both need to go on the * on the Nest.
Here are some pics.
Thank you Ken.
Few more questions:
1. It looks like OB and Aux both go to the heat pump. W3 looks to go to the furnace. Attaching clearer pics of the wiring on the right of the EIM (Equipment Interface Module) as well as another pic of wiring for the EIM / HP / Furnace. Does this look / sound correct to you? Also, the green highlighted area of the annotated image of the wiring diagram for the EIM has been my biggest uncertainty. But, you're helping to clarify it for me.
2. There are two Humidity wires as shown in the yellow highlighted section. Looking at the left pic of the EIM, it looks like H1 also goes to C. So, my guess is that the red wire goes to C and the white wire goes to *. Does this sound correct?
3. I have attached annotated screenshots of both the Nest wiring diagram and the EIM wiring diagram with numbers of what I understand of which wire on the EIM goes to which terminal on the Nest. Does this look correct to you?
Please let me know.
Thanks
Earthtraveler5,
I guess it’s time now for the ugly truth, lol.
Your Goodman heat pump has a reversing valve that when not energized the system is in heating mode. To get AC cooling mode you have to energize the reversing valve on the OB terminal. When your heat pump is in heating mode, the defrost control board temperature sensor closes at 31°F, that is sensing ice on the coil, and that initiates the defrost cycle and the defrost control board then sends a control call on the W2 wire of the outdoor defrost controller to the indoor unit to activate the auxiliary heating, in your case the gas furnace. In systems that do not have gas heat they have the indoor coil and usually 15kW to 45KkW of electric heating strips that are the auxiliary/emergency heat.
You sort of have the best of two worlds, depends if gas or electricity is less expensive per equivalent BTU of heat to heat your house. The problem is a normal thermostat does not have the intelligence to make that decision for you. In the case of the Nest, and most smart thermostats, when it is programmed as controlling a heat pump it can only assume that there is auxiliary and or emergency heating. Furthermore, the thermostat considers the heat pump as the primary mode of heat. As a homeowner you will only be able to get gas heating when you place your thermostat in emergency heat or auxiliary heat mode. Otherwise the heat pump will be your primary motive heat and it will only signal the gas to come on when the outdoor unit enters defrost cycle.
The outdoor unit connection points are only C, Y, R, W2, G. This picture below, from the installation manual, shows the Heat Pump Low Voltage Junction Box.
Now let’s talk about the humidifier, the humidifier has as you understood correctly, two wires one is common and one is control voltage. The humidifier is a self-contained unit that has a humidistat and a setting that the homeowner can place for the desired humidity level during heating periods. The most desired heating percentage is 50% typically. When the control wire is activated it signals to the humidifier to turn on and using the humidistat will measure the humidity and if it’s below the desired level it will activate the humidifier function. We only need to send one wire from the thermostat there and that will be the red wire and the white wire will be connected to the common in the furnace.
The wires you have numbered will need some adjustment, #5 wire will not be used, the #6 (W2) from the furnace and outdoor unit will go to the W2(#5) position in the thermostat. All the other wires, as you deduced are correct.
when you go through the Nest online configuration tool you will list the wires that on your old thermostat are as follows. Rc, C, Y1, W2, O/B, G, HUM.
Ken, The AC Cooling Wizard
Hi Ken,
In this photo, OB (4) is from the heat pump.
AUX (5) is also from the heat pump.
AUX2 (6) is from the furnace.
So, 4 goes to OB. 5 goes to W1. 6 goes to W2?
Where is emergency heat on the Nest? Is that W2 or somewhere else?
Yes, correct.
The yellow, green, and white wires that go to the top left go to the outdoor unit. The yellow, green, and white wires that go to the bottom left go to the furnace.
Here is a picture I created to kind of show you how the wires will run from unit to unit to unit I hope this helps you understand how to wire it.
CoolingWizard
You're awesome!! Thanks!!
I wish I could give you that Nest Pro payment.
Here it is. Everything tested good. How does it look?
The wiring is a bit of a mess but I think it's all connected correctly.
The wires are not long enough to terminate them at the furnace.
I believe this is how to enable emergency heat or alternate heat, correct?
Like this, correct? When the temp falls below 25, use the alternate heat source, gas.
Do you have a suggestion of the optimal temp to set it to?
