8 wire Honeywell thermostat

[Montmont66]

• I have a heat pump and have an 8 wire Honeywell thermostat, are all the wires used for the Nest thermostat?

[CoolingWizard]

 Montmknt66.  Your system has a remote sensor that this Honeywell thermostat uses to make heating and cooling decisions and the jumper between R and Rc will not be used.  Also, the two wires connected to “S” will not be needed by the Nest Learning Thermostat 3rd Generation.  Your wires for the Nest will be:

R - red wire; Power-IN

O - wire color?; Heat Pump Reversing Valve 

Y - Yellow Wire; Compressor Contactor

G - Light Green Wire; Indoor Blower Fan Control

B - Blue Wire; Power COMMON

W1 - White Wire; Auxiliary Heating control

The two wires on S1 and S2 will not be needed. 

Your W1 is most likely your auxiliary or emergency heat. Heat pumps, when in heating mode, will ice up the outdoor  coil, when that happens, the outdoor coil will signal indoor fan, and switch to cooling mode to warm up the outdoor coil melt the ice.  During the defrost time, the Auxiliary heat is activated to keep the air warm.  In most heat pump system this auxiliary heat is Electric Heating Coils in the indoor air handler.  

Ken, The AC Cooling Wizard

[Montmont66]

Thank you, to confirm the green and white wires on S1 and S2 will not be needed? Are they required for the auxiliary heat during defrost time? Also, looks like there’s a jumper on RC and R, will that be needed?

[EdwardT]

Hi folks,

@CoolingWizard, thanks for the help!

@Montmont66, thanks for reaching out. In some cases the S1 and S2 wires provide outside temperature to the thermostat. This is not compatible with your Nest Thermostat since it gets its outside temperature information from the internet. Also, you don't need to put the jumper wire. Nest Learning Thermostats use an internal jumper between the Rh and Rc connectors. A Nest Learning Thermostat will automatically use this internal jumper if your system needs it.

Thanks,

Edward

[CoolingWizard]

Montmont66, No the S1/S2 on the Honeywell is only used to tell the homeowner the outside air temperature.  The auxiliary heat is selected by the indoor air handler and there is a signal wire form the outdoor unit telling the indoor unit that the defrost cycle is active.  At the thermostat, homeowners can initiate the auxiliary heat in , for example, a winter emergency like the outdoor unit failing.  This way you can have some heat until it gets fixed.  
Ken, The AC Cooling Wizard. 

[Markjosephp]

Hi folks,

Thanks for the assistance, @EdwardT and @CoolingWizard.

@Montmont66, I'm checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns.

Best regards,

Mark

[Markjosephp]

Hello Montmont66,

It has been a few days since the last reply, and I am going to lock the thread within 24 hours. If you have any questions, please feel free to create a new post.

Best regards,

Mark