# help with installation of Honeywell RTH8500 thermostat



## gregzoll (Dec 25, 2006)

See replies in http://www.diychatroom.com/showthread.php?t=31804


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## pbservano (Nov 11, 2008)

dg xy said:


> Hi, I have a heat pump with electrical furnace. It was working well until I tried to replace the old thermostat (31F3201) with the new programmable RTH8500. The wiring are connected according to the instruction from Honeywell Tech Support (old to new):
> 
> X-c; VR-R; R-O/B; F-G; L-L; M-Y; Y-Aux; A - not connected to anything.
> 
> The system is not working at all. This means that there is not heat and the compressor is not work. Any advice would be appreciated.


I'm assuming that you have a split system. You should have at least the following wires coming out from your wall. Red, White, Green, yellow, Orange, and Blue wires.

Connect wires:
Red - to terminal R (leave the jumper on the thermostat terminal to RC)
Blue - to terminal C ( this should be your -24VAC common wire). If you have a multimeter, set your meter to VAC and measure voltage between Red and Blue, you should read 24-28VAC control voltage.
Green - to terminal G, this is your wire for your blower (fan).
Yellow - to terminal Y, this wire is to power up your 24VAC contactor in your outdoor unit during heating and cooling. 
Orange - to terminal O/B, this is your wire when your system is in cooling mode. This wire is powered up during cooling only. Most unit operate during heating mode with this wire de-energized (no power).
White - to terminal AUX, install jumper wire to E ( E, is for your emergency mode, electric heat is powered up). Your white wire is energized when your unit goes on defrost mode energizing your electric heat and demand for heat load is required.

Don't forget to configure your unit by going thru the codes and changing them appropriately for heat pump operation. Read the programming mode carefully don't rush. Also don't forget to remove the tab to activate the batteries.


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## dg xy (Nov 13, 2008)

pbservano said:


> I'm assuming that you have a split system. You should have at least the following wires coming out from your wall. Red, White, Green, yellow, Orange, and Blue wires.
> 
> Connect wires:
> Red - to terminal R (leave the jumper on the thermostat terminal to RC)
> ...


 
Thanks to you and the other guys for your prompt reply and knowledgeable answers. The guy who did the installation did not follow the color codes at all. I had to call an electrician and he spent like 2 hours working on it to figure out all the wiring labels. In the end, he connected the wires as follows:

VR-R and R-jumpered to RC
R-O/B
M-Y
F-G
X-C
L-L


He wanted to connected Y to Aux but the heat pump would stop after less than 2 minutes and aux heat would come on, something not normal when it is 10 C abover zero outside. In the end, he left Y unconnected and told me that he would call one of his buddies for some advice on that. He did put a jumper between Aux and E and told me that AUX and E would come on when the heat pump stop working at low ambient temperature outside. For now, I have to take his words for it and am all happy that the heat pump is working to keep my house warm. 

The connection he did was almost the same as what I did following the tech support's instruction. But he was able to find out why my installation failed to work. Basically,the security mechanism in the system kicked in and disconnected the system from the thermostat to protect the heat pump. That might have happened during my first attempt, in which I did the installation the way HomeDepot electrician told me (I had to install it again after I phoned the tech support). During the process, i might have connected the wrong wires together and the protective mechanism kicked in. I was happy that he identified the problem and that I did not break the whole system. 

He sounded to be a decent fellow and I paid him for two hours of labor, which might be a little on the high end because someone like you may not need two hours to fix it. Anyhow, I paid him because he did spend two hours and also vacuumed my system for me. Besides, the Lennox people told me that they would charge 1.5hr just to come and find out what my old thermostat was and which new thermostat I should put on, not to mention to install the new one. 

Sorry for the lengthy re. One more question, HonWell tech support told me to connect Y to Aux to E. The person who did the re-installation last night said no because Y is for cooling. What do you think? 

Thanks a lot again.


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## kennzz05 (Nov 11, 2008)

as pbservano told you no you cannot hook y to aux, y runs the outdoor unit for both heat and a/c . aux is the elec backup heat its too bad the terminal designations arent following the industry standard as it makes it harder to tell you where to put them


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## dg xy (Nov 13, 2008)

kennzz05 said:


> as pbservano told you no you cannot hook y to aux, y runs the outdoor unit for both heat and a/c . aux is the elec backup heat its too bad the terminal designations arent following the industry standard as it makes it harder to tell you where to put them


Thanks. Sorry, I was not clear about the question in my last post. 

Now the wires are connected as follows (old lennox labels - new honeywell labels):

VR-R and R-jumpered to RC
R-O/B
M-Y
F-G
X-C
L-L

Besides that the tech support guy told me to connet 

Y (old)-AUX (new).

then put a jumper between the new Y and AUX, and also between AUX and E. 
Does that make sense?

Thanks,
DG


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## kennzz05 (Nov 11, 2008)

gregzoll said:


> See replies in http://www.diychatroom.com/showthread.php?t=31804


ok i am looking at the manual that was supposed to come with your stat and i dont see the designations your using just the regular color codes

where are you getting vr, m f x ?? i see r/rc, o/b, y, g, c, e/aux
r/rc goes to the red wire (POWER) o/b orange wire(REVERSING VALVE) y/ yellow wire (OUTSIDE UNIT) g/green wire (FAN)
c/blue or black (COMMON) e/aux white wire (ELEC HEAT)

this gets repeated at the air handler and outdoor unit


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## pbservano (Nov 11, 2008)

dg xy said:


> Thanks. Sorry, I was not clear about the question in my last post.
> 
> Now the wires are connected as follows (old lennox labels - new honeywell labels):
> 
> ...


DG

I need you to do this for me. Trace the wire M, Y, and R all the way to the indoor unit and also from the indoor unit to the outdoor unit. These wires is very important to be connected correctly for your system to function properly. If you have a digital camera I'd like you to take picture of the electrical schematic diagram of the indoor unit and the outdoor unit they are located at the cover for the outdoor unit and at the front blower for the indoor unit. Also, give me the model number of both units. Here's my e-mail address, [email protected]. Take as much pictures of the indoor unit the way the control wires are connected at the control board of the indoor unit and if possible the control wires connected at the outdoor unit. Send these pictures to me.


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## dg xy (Nov 13, 2008)

kennzz05 said:


> ok i am looking at the manual that was supposed to come with your stat and i dont see the designations your using just the regular color codes
> 
> where are you getting vr, m f x ?? i see r/rc, o/b, y, g, c, e/aux
> r/rc goes to the red wire (POWER) o/b orange wire(REVERSING VALVE) y/ yellow wire (OUTSIDE UNIT) g/green wire (FAN)
> ...


Thanks. Yes I know it is confusing because the Lennox system is probably more than 20 yr old and used different labels. Moreover, the wire codes were not followed. I sent the diagram and the pictures for the wiring of the both old and new thermostats to pbservano for his opinion. Thanks again, 
DG


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## belacan (Nov 16, 2008)

Hi, I'm a newbie here, looking for some advice on replacing my old White-Rodgers thermostat 1E30W-311 with the Honeywell RTH8500. I have read the manuals however on pulling the old thermostat out, I discovered that I only have 2 unlabelled wires. How do I connect these wires to the RTH8500?

Thanks.


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## kennzz05 (Nov 11, 2008)

belacan said:


> Hi, I'm a newbie here, looking for some advice on replacing my old White-Rodgers thermostat 1E30W-311 with the Honeywell RTH8500. I have read the manuals however on pulling the old thermostat out, I discovered that I only have 2 unlabelled wires. How do I connect these wires to the RTH8500?
> 
> Thanks.


 
more info please, type of heat,gas, heat pump, straight electric what colors are in question many times there are extra unused wires


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## gregzoll (Dec 25, 2006)

Write down the colors at the Thermostat, then go down to to the Air Handler and write down what colors go to what terminals. From there, if you have the book for the Air Handler, it can also help to know what terminals go to what to help with the labeling of the Thermostat end. Majority of the time, everything matches color for color up at the thermostat, but just in those cases that someone did not do it right the first time, books come in real handy, along with taking the time to look at the wiring on both ends.


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## belacan (Nov 16, 2008)

kennzz05 said:


> more info please, type of heat,gas, heat pump, straight electric what colors are in question many times there are extra unused wires


My existing thermostat only controls the gas furnace and there are only two wires, white and black.
Also, does anybody know how to switch the RTH8500 temperature reading from F to C?

Thanks.


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## pbservano (Nov 11, 2008)

belacan said:


> My existing thermostat only controls the gas furnace and there are only two wires, white and black.
> Also, does anybody know how to switch the RTH8500 temperature reading from F to C?
> 
> Thanks.


You need an extra wire to the neutral 24VAC to power up your rth 8500, this wire should be connected to "C" terminal board, test the BLACK and White wires that you have now. Identify which one is going to your gas valve and connect this to "W" terminal.


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## pbservano (Nov 11, 2008)

pbservano said:


> You need an extra wire to the neutral 24VAC to power up your rth 8500, this wire should be connected to "C" terminal board, test the BLACK and White wires that you have now. Identify which one is going to your gas valve and connect this to "W" terminal.


Correction on terminal connection, conect the wire that goes to the gas valve to terminal "Y" instead. The "W" terminal is used for back-up heat.


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## schlorraine (Jul 28, 2009)

*So?*



pbservano said:


> DG
> 
> I need you to do this for me. Trace the wire M, Y, and R all the way to the indoor unit and also from the indoor unit to the outdoor unit. These wires is very important to be connected correctly for your system to function properly. If you have a digital camera I'd like you to take picture of the electrical schematic diagram of the indoor unit and the outdoor unit they are located at the cover for the outdoor unit and at the front blower for the indoor unit. Also, give me the model number of both units. Here's my e-mail address, [email protected]. Take as much pictures of the indoor unit the way the control wires are connected at the control board of the indoor unit and if possible the control wires connected at the outdoor unit. Send these pictures to me.


Exact same problem here. Can you guys please share the final connections used?

Thanks!


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## gregzoll (Dec 25, 2006)

Read the book.


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## schlorraine (Jul 28, 2009)

gregzoll said:


> Read the book.


Sorry Gregzoll, I may not have been clear in my request. The whole purpose of this thread is that the labels do not match with those described in the book, which I read thoroughly. I happen to have the exact same old thermostat than dg and you did not did not confirm on this thread what should be the final connections.

With the following documents, http://www.iaqwholesale.com/manuals/IAQmanuals/Honeywell/SubBases/Q674/60-2485.pdf, http://www.transition.honeywell.com/documents/Complete%20Transitioning%20Thermostat%20Cross%20Reference%20Table.XLS and http://www.lennox.com/pdfs/installation_maintenance/Lennox-HP19-IOM.pdf, i came to v-vr->r, m->y, f->g, x->b->c, y->w->aux, a->T, r->o->o/b, L as is.

In essence, it is the same ad DG. Now, I did not find anything about the E (emergency heat) to aux jumper. Is it required and why?

I am also puzzled to leave the a / t wire capped since I understand it comes from the outdoor thermistor. What is the role of it? Is the heat pump self protected for low temp is it the thermostat supposed to stop wihen outdoor temp is low, with the help of this thermistor?

Finally, what is the L wire for?

I hope this more complete question will deserve a more complete answer!

Thanks for you help

Schlorraine.


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## gregzoll (Dec 25, 2006)

The way you solve it, is by opening your own thread, if you 1) Cannot create a diagram of what colors connect on the furnace, and then at the Thermostat. Your problem can be solved by reading the book and looking at both ends, for what color connects where. If you disconnected the thermostat first, without labeling, that is your fault, not the books, because it even tells in step one, to use the labels enclosed or use masking tape to label terminal connections.


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## schlorraine (Jul 28, 2009)

It seems my english is really poor.

I connected everything correctly, all labelled, all good, and it works. I just have label a/t which I cannot connect, same as the guy who opened the thread, and I am concerned about the fact that the honeywell 8500D does not use the outdoor thermistor. I was wondering if it could damage the heat pumb when the weather gets really cold, but apparently I wont get an answer here. Thanks anyways.

I did not blame anyone neither the books nor you for answering without reading my posts.

But hey, I'll find somebody else. Thanks anyways for this thread, it did put me on the right track!


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