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Old 09-16-2019, 11:29 AM   #1
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10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


I need to upgrade our old Honeywell T874R1350 LR1620 30V MAX thermostat running the 30-years old ZoneAire heat pump with any "smart" (WI-FI or Z-Wave) thermostat. I was thinking to use Honeywell RTH9585WF.

The unit is a wall hung heat pump, similar to the Bard brand. There are original heat pump and original thermostat Honeywell T874R installed when the condo was built in 1987. I have a picture of the wiring on my old thermostat, stats for the new one and a sketch for a heat pump. According to what I could see, the are 10 wires as follows (I tried to match the colors with the letters and not sure if they're correct):

W3 – grey – auxiliary heat
W2 – white – heating
G – green – indoor blower
L – blue – compressor fault relay
R – red – energy (power)
B – brown – defrost relay
Y – yellow – compressor relay
O – black – prevalent
E – orange – emergency heat
X2 & X1 (connected together) – pink – ?

My new stat on Honeywell RTH9585WF has:
C ------------ R -red
K ------------ W2 – white – heating
RC
R ------------ O – black – prevalent
W-O/B ----- B – brown – defrost relay
Y ------------ Y – yellow – compressor relay
G ------------ G – green – indoor blower
W2-Ux/E -- E – orange – emergency heat
Y2 ----------- W2 – white – heating
L ------------- L – blue – compressor fault relay

Please correct me if I am wrong. What should I do with X2 & X1?

Thanks
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Old 09-16-2019, 02:05 PM   #2
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


your existing stat stages the aux heat - no retail stat supports that.

You'll need a stat with aux heat staging and an E terminal. I see a separate emergency heat relay so you actually need the E terminal - in other cases it's redundant.

I caution you - with a heatpump it's better to maintain a constant temperature rather than raise and low it.

edit: i'm unclear on why it has aux heat staging when elements are not wired for that in diagram.
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Old 09-16-2019, 02:29 PM   #3
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


My interpretation:

W3 – grey – second stage aux heat
W2 – white – first stage aux heat
G – green – indoor blower
L – blue – compressor fault light
R – red – energy (power)
B – brown – reversing valve, energized in heat mode
Y – yellow – compressor relay
O – black – emergency heat indicator light - new stat will not have this, tape off
E – orange – emergency heat
X2 & X1 (connected together) – pink – common

new stat will have to be programmed for your application.
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Old 09-16-2019, 03:07 PM   #4
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


i don't see any wifi stats with a dedicated E terminal but the emergency heat relay doesn't seem to have much function aside from turning on an indicator light.

W3 looks redundant too, there's only one aux heat contactor. emergency heat has to be on for power to be passed from W3 to aux heat contactor and W2 connects directly anyway.

You may be able to use the retail stat after all - wait for more replies.
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Old 09-16-2019, 03:17 PM   #5
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


May I ask why you want to replace the thermostat in the first place? Is there a problem with your existing thermostat?
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Old 09-16-2019, 03:53 PM   #6
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Thanks alot for your input! This old thermostat is working well in our vacation house at the lake in Poconos, PA. I just need to have an access to control the temperature when we're not there. Our electric bill last winter was crazy high and most of the time we weren't there. So, I can follow your instructions and use Honeywell RTH9585, right? Thank you!
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Old 09-16-2019, 07:38 PM   #7
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


I'm unclear on why it has a separate connection for W3 when the electric heat is not staged and why the W3 wire goes through the aux heat relay.

If W3 and E are redundant in your case and add no functionality, they can be taped off and that thermostat used.

But like I said before, wait for more replies - there may be something I don't know about this unit.


I'm betting the use of aux heat in a winter climate is what's driving up the utility use.

There are better thermostats for heatpumps that can do more than that expensive retail model - like lock out the aux heat above a certain outdoor temperature and set up a droop (temperature drop below setting) before it comes on.

How are you running it now?
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Old 09-17-2019, 05:37 AM   #8
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


The E terminal on that unit, when energized, does not bring on the emergency heat. It only closes a contactor, so that the emergency heat can work when the thermostat energizes the W3 terminal. So that the house doesn't drop an extra 2 degrees before the heat comes on.


Consider getting a Honeywell IAQ thermostat. And then locking out the aux heat, until outdoor temps drop to X degrees.


Remember, if you set back the temp when you aren't there. And then raise it 10 or more degrees when you arrive. It will use the aux heat for hours to get the temp back up. Which can give you a very high bill for just being there on weekends.
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Old 09-17-2019, 06:41 AM   #9
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


My suggestion is to use the ecobee. It's very good at not using aux heat.

Cheers!
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Old 09-17-2019, 07:47 AM   #10
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


I bought Honeywell THX9421 Prestigeฎ IAQ with EIM and still have it but couldn't figure it out and decided to get the retail one Honeywell RTH9585WF.

Our vacation house is a 2-bedroom condo by the lake in Poconos, PA. We have 4 thermostats there: 3 baseboard heaters already on Stelpro KI STZW402WB+(Z-wave) - one in each bedroom and one in the dining room; and 1 thermostat (Honeywell T874R in the hallway for ZoneAire heat pump (the unit is a wall hung heat pump, similar to the Bard brand).
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Old 09-17-2019, 07:54 AM   #11
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


Quote:
Originally Posted by Janebull View Post
I bought Honeywell THX9421 Prestige IAQ with EIM and still have it but couldn't figure it out and decided to get the retail one Honeywell RTH9585WF.

Our vacation house is a 2-bedroom condo by the lake in Poconos, PA. We have 4 thermostats there: 3 baseboard heaters already on Stelpro KI STZW402WB+(Z-wave) - one in each bedroom and one in the dining room; and 1 thermostat (Honeywell T874R in the hallway for ZoneAire heat pump (the unit is a wall hung heat pump, similar to the Bard brand).
The thx will have more options. It only knows outdoor temp when you install an opinional sensor. It will bring on aux heat whenever you try to bring it out of recovery.

Cheers!
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Old 09-17-2019, 07:57 AM   #12
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


Quote:
Originally Posted by user_12345a View Post
I'm unclear on why it has a separate connection for W3 when the electric heat is not staged and why the W3 wire goes through the aux heat relay.

If W3 and E are redundant in your case and add no functionality, they can be taped off and that thermostat used.

But like I said before, wait for more replies - there may be something I don't know about this unit.


I'm betting the use of aux heat in a winter climate is what's driving up the utility use.

There are better thermostats for heatpumps that can do more than that expensive retail model - like lock out the aux heat above a certain outdoor temperature and set up a droop (temperature drop below setting) before it comes on.

How are you running it now?
What are the other better thermostats that I can look at? Please advise. Thanks
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Old 09-17-2019, 08:05 AM   #13
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


Quote:
Originally Posted by Janebull View Post
What are the other better thermostats that I can look at? Please advise. Thanks
The thx9421 is redlink enabled, so it can use wireless outdoor sensors. I didn't look at the other stat that you have. Once it reads the outdoor sensor, you can set a lockout temp. Without the sensor, the setting is not visible.

Ecobee uses internet weather stations.

Cheers!
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Old 09-17-2019, 08:14 AM   #14
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


Do note that the ecobee and the thx9421 isn't zwave enabled. They both have internet APIs that allow things like wink to connect to them. The Honeywell requires an internet gateway (Sometimes sold separate, but is included in some kits.) to be internet connected....

Cheers!
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Last edited by supers05; 09-17-2019 at 08:18 AM.
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Old 09-17-2019, 08:40 AM   #15
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Re: 10-wires Honeywell T874R to RTH9585WF on Bard or ZoneAire Heat Pump?


Quote:
Originally Posted by supers05 View Post
The thx will have more options. It only knows outdoor temp when you install an opinional sensor. It will bring on aux heat whenever you try to bring it out of recovery.

Cheers!
It's way too complicated (THX) and probably not necessary in my situation. I'm hopping to install RTH9585 with W3, E and O taped off and the rest of the wires (7) would be connected as follows:

W2 – white – first stage aux heat - W/O/B
G – green – indoor blower - G
L – blue – compressor fault light - L
R – red – energy (power) - R
B – brown – reversing valve, energized in heat mode - W2/Aux/E
Y – yellow – compressor relay - Y
X2 & X1 (connected together) – pink – common - C

Please correct me if I'm wrong. Thank you!
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