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BillyHvac
BillyHvac, Journeyman HVAC Tech
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I am replacing the old Rodgers with a Honeywell RTH6500

Customer Question

I am replacing the old White Rodgers with a Honeywell RTH6500 Wi-Fi. The old one does not have a C wire. I connect the existing B wire to C terminal and the O wire to O/B and the rest of the wires as follow G to G, Y to Y, W to AUX, Red wire to R & Rc (jumped). When I turned the power on I hear a humming from the furnace (up in the attic) even if the thermostat is set to off. The humming last all day. It was not like this before. Did I make all the right connections? I also set the function on the new as Heat pump. Is this correct? I understand if I have O & B wires (separate) then I have a heat pump system. My furnace is a forced air Gram with the A/C unit next to it. My house was built in 1998.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

What is model on old thermostat?

Expert:  airheatman replied 1 year ago.

Also what is model on the outdoor unit? That will tell me if it is a heat pump.

Customer: replied 1 year ago.
The old thermostat is White-Rodgers 1F80-24 (?). The A/C is Bryan model either 561C, 561N or 561W. The furnace is Ama forced air with product # ***** model # ***** There is a gas pipe going into the furnace. I just found out that the furnace was running even my Honeywell is off because the thermostat on my second floor (same White-Rodgers) is on. When I turned it off, the screen of the Honeywell downstairs went blank. I just want to use the Honeywell Wi-Fi downstairs. I do not care much about the old one upstairs. What should I do?
Customer: replied 1 year ago.
The White-Rodgers upstairs has only 3 wire connected (W, Y and Red (jumped from RC to RH)). I was trying to disconnect them all and the Honeywell went blank.
Expert:  airheatman replied 1 year ago.

Ok first of all, your system is definitely not a heat pump so we want 0 selected as system type.

But we have an issue here with this second thermostat being in the circuit.

Normally if you have a second thermostat it is operating zone dampers for upstairs.

The 0 terminal is for energizing the reversing valve in a heat pump and not used with a conventional system.

It sounds like previous installer may have been using that O terminal somehow to connect the second thermostat.

I am not familiar with how that is done so I am going to open this to other experts who may be more familiar with the setup.I did not realize there was a second thermostat.

I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk.Please stand by to see if another expert can assist further.

Expert:  HVAC Guru replied 1 year ago.

Hello,

If you had a separate O and B terminal on the old unit you really need to get a thermostat with a separate O and B terminal as these older systems can not run like a newer unit just getting rid of the B and taping it off.

Customer: replied 1 year ago.
The Honeywell tech told me that it can be done. Since I have B and O wires separately then I should have a heat pump system. The user guide told us to install B wire to C terminal and O wire to O/B terminal. Is this correct?
Customer: replied 1 year ago.
How do I find out if my system is a heat pump type or not?
Expert:  HVAC Guru replied 1 year ago.

If you have an O and B wire it has to be a heat pump system

Expert:  BillyHvac replied 1 year ago.

That is incorrect...having an Oand B wire does NOT mean you have a heat pump.

The Bryant 561 is a regular ac unit

The 373 furnace is regular gas furnace

The reason you have an O and B is because you are running a zone system. The o and b are terminals that go live in either heating as an accessory or cooling as an accessory.

You do NOT have a heat pump...you have a zoned system. You cannot use the wifi in place of the current thermostat as it is a "Master" and the other thermostat is secondary..meaning it can only do what the master lets it do.

Expert:  BillyHvac replied 1 year ago.

That is incorrect...having an Oand B wire does NOT mean you have a heat pump.

The Bryant 561 is a regular ac unit

The 373 furnace is regular gas furnace

The reason you have an O and B is because you are running a zone system. The o and b are terminals that go live in either heating as an accessory or cooling as an accessory.

You do NOT have a heat pump...you have a zoned system. You cannot use the wifi in place of the current thermostat as it is a "Master" and the other thermostat is secondary..meaning it can only do what the master lets it do.

Customer: replied 1 year ago.
I check at the furnace system and the wires are connected as follow.
1. The thermostat upstairs has only 2 wires connected. W (white) wire to COM 24U terminal, R (red) wire to Y terminal (connected to the same terminal with Y wire from downstairs). The G (green) is not used and is taped.
2. The thermostat downstairs has 6 wires connected. Y (yellow) to Y terminal, R (red) to R, G (green) to G, W (white) to W, especially B (blue) to red wire and O (brown) to green wire coming from 1 1/2 inches block with coil wires (I have no idea what it is).
With these wirings do you mean that I cannot use the Honeywell Wi-Fi thermostat? Initially after connecting the new Honeywell thermostat (G to G terminal, Y to Y, W to AUX, R to R jumped to Rc, B to C and O to O/B) I can set up the Wi-Fi and control the thermostat through my cell phone by turning the heat on and off and setting the temperatures.. After turning it on for a while then turning it off by cell phone the furnace stop but I still heard a humming sound from the system. Later when I tried to turn it on and off again, this time the furnace were still running. I realized at that time that I did switch the thermostat upstairs to ON all that time. When I switched it of, the one downstairs went blank. What does this mean?
Customer: replied 1 year ago.
Can I change the wiring somehow to make it works?
Customer: replied 1 year ago.
What is the block that wires O and B connected to as I mentioned above?
Expert:  BillyHvac replied 1 year ago.

It is the way you are configured. You have 2 thermostats without a zone panel...the block with coil wires is a relay..that is deciding which thermostat is operational.

The B terminal activates with heat and the o terminal with cool. The issue is that the main thermostat overrides the 3 wire....the wire is known as a slave because it can only operate when the master thermostat is not.

End result is if you want wifi on the master you need different terminals for o/b...or do away with the second thermostat and let the master control the entire house.

Expert:  HVAC Guru replied 1 year ago.

Yes like I stated you will need a thermostat with the O and B separate to run it

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Expert:  BillyHvac replied 1 year ago.

Unfortunately the o/b is NOT for heat pump as previous peer mistakenly noted.

Here the O and B are accessories...Not a O and B (common) as evident by "taping off" comment.

So in summary, the unit is not a heat pump as instructed.....the b terminal is not one that can be taped off as instructed

They use the relay to differentiate between what thermostat is given control...

If you have further questions ask for Billy as I recognized that you had a dual thermostat arrangement and not a heat pump.

Billy

Expert:  HVAC Guru replied 1 year ago.

Yes like I stated you will need a thermostat with the O and B separate to run it

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me forFREE follow up questions and tips are greatly appreciated! Thanks

Expert:  BillyHvac replied 1 year ago.

Unfortunately the o/b is NOT for heat pump as previously noted.

Here the O and B are accessories...Not a O and B (common) as evident by "taping off" comment.

So in summary, the unit is not a heat pump as instructed.....the b terminal is not one that can be taped off as instructed

They use the relay to differentiate between what thermostat is given control...

If you have further questions ask for Billy as I recognized that you had a dual thermostat arrangement and not a heat pump.

Billy

report filed

Customer: replied 1 year ago.
Billy,
With all the talk back and forth, I still did not get the main answer for my question: how to make my Honeywell RTH 6500 Wi-Fi work with the existing system. In summary, now that I understand I have a heat/cool, not a heat pump system, I have 2 thermostats with a relay that is deciding which one is operational. If I cannot use both, I am willing to get the one upstairs disconnected and use only the one downstairs. How can I do that without having to buy a different thermostat. Can I change the connection at the control board and at the thermostat? Again here are the existing connections at both ends right now.
A. AT THE CONTROL BOARD:
1) Coming from the thermostat upstairs only 2 wires are connected. W (white) wire to COM 24U terminal, R (red) wire to Y terminal (connected to the same terminal with Y wire from downstairs). G (green) is not used and is taped.
2) Coming from the thermostat downstairs 4 wires are connected. Y (yellow) to Y terminal, R (red) to R, G (green) to G, W (white) to W. The B (blue) is connected to the Red wire and the O (brown) to the Green wire coming from the relay.
A. AT THE DOWNSTAIRS THERMOSTAT:
1) 6 wires were connected to my old White-Rodgers (model 1F80-24) as follow: W (white) to W, G (green) to G, Y (yellow) to Y, R (red) to Rc jumped to Rh, B (blue) to B and O (brown) to O terminal. The last 2 were connected to the relay as mentioned above.
2) The new Honeywell thermostat has the following terminals: K, Y2, W2, G, W, C, Y, R and Rc. This thermostat requires a C wire for power. I do not have one. How do I make all the connections, especially to have power for the C wire.
If you cannot make it work then I should not pay for the service. If it can help I can send the pictures. Just tell me how.
Thx. Quang
Expert:  BillyHvac replied 1 year ago.

If you are willing to change the system we can use the thermostat.

Do you know if you have any dampers in the system to separate zones or simply have 2 different thermostats for one furnace?

Customer: replied 1 year ago.
I think I just have 2 thermostats for 1 furnace. Since I bought the house, I only use the one downstairs.
Customer: replied 1 year ago.
How come when I receive your e-mail and click on the link "view the answer" it keep telling me that "this page can't be displayed".
Expert:  BillyHvac replied 1 year ago.

Ok,

we are going to do away with the upstairs thermostat and the relay.

remove existing thermostat.

Install wifi and wire as follows:

red to R/Rc

white to W

Yellow to Y

Green to G

Blue to C.

Now at furnace....

red to R

white to W

yellow to Y

green to g

blue to C

Do not use brown

This will connect main thermostat direct to furnace/ac and give complete control and wifi

Billy

Expert:  BillyHvac replied 1 year ago.

Ok,

we are going to do away with the upstairs thermostat and the relay.

remove existing thermostat.

Install wifi and wire as follows:

red to R/Rc

white to W

Yellow to Y

Green to G

Blue to C.

Now at furnace....

red to R

white to W

yellow to Y

green to g

blue to C

Do not use brown

This will connect main thermostat direct to furnace/ac and give complete control and wifi

Billy

Customer: replied 1 year ago.
I do not have a C terminal at the furnace.
Expert:  BillyHvac replied 1 year ago.

you do..it may be labeled Com....

Expert:  BillyHvac replied 1 year ago.

if you have ac...two wires come into furnace from outside...one goes to Y with yellow from thermostat and the other goes to C (com)

C= common

Com = common

Customer: replied 1 year ago.
Bill,
Ok. So the terminal COM 24U is C? I do have that. At the furnace I just remove and tape all the wires coming from the thermostat upstairs. Should it be good enough? It's late now. I'll do it tomorrow and let you know. Thank you for your patient.
Expert:  BillyHvac replied 1 year ago.

you are correct..just tape off all the other wires.

You see the thermostats really cancel each other in this design.

Lets say down stairs is warm enough, but upstairs needs heat...all it does is turn the furnace on until the upstairs is warm..which overheats the downstairs...

So really in your case you just want one thermostat anyway.

Wire as described and just get back to me...make sure furnace is off when proceeding

Customer: replied 1 year ago.
I have an AC. What outside wires are you talking about? I did not see any beside the ones I describe to you.
Expert:  BillyHvac replied 1 year ago.

in the furnace...there should be 2 wires that come from outside.

One will attach to Y and the other to Com.

Customer: replied 1 year ago.
I'll check again tomorrow. How do they look like?
Expert:  BillyHvac replied 1 year ago.

just like the thermostat wires.

Follow the 2 pipes from ac coil on the furnace...one is covered in black rubber...there should be a wire that runs with it.

Customer: replied 1 year ago.
Are they connected to something right now?
Expert:  BillyHvac replied 1 year ago.

the Com terminal should have one of the ac wires in it.

is the Com currently empty or has a wire?

Customer: replied 1 year ago.
It has the W wire from the thermostat upstairs.
Expert:  BillyHvac replied 1 year ago.

so someone has rigged the thermostat for cooling to upstairs stat and heating from downstairs.

Post a pic of the wiring in furnace tomorrow and I can see and direct easily.

Customer: replied 1 year ago.
How to post pictures?
Customer: replied 1 year ago.
By adding files?
Expert:  BillyHvac replied 1 year ago.

use the attach file link...or it may even be a paperclip...or use a file share site like flikr. tumblr, mediafire..etc

Customer: replied 1 year ago.
Attached are the pics of the terminals at the furnace. As you can see there are 2 sets of wires. One from the thermostat upstairs with W (white) to COM and R (red) to Y. The other set from the one downstairs: W (white) to W, Y (yellow) to Y, R (red) to R and G (green) to G.
Expert:  BillyHvac replied 1 year ago.

yep...you going to have a wire nut somewhere joining wires...

The end result is this..

we need 5 wires from the thermostat (wifi) to furnace.

from furnace out to ac we need 2 wires...I am not talking about main power wires...but thermostat wires like shown.

We can forget/abandon the upstairs wires and thermostat...but we need the 5 from furnace to thermostat and 2 from furnace to outdoor ac.

Customer: replied 1 year ago.
yep...you going to have a wire nut somewhere joining wires...The end result is this..we need 5 wires from the thermostat (wifi) to furnace.from furnace out to ac we need 2 wires...I am not talking about main power wires...but thermostat wires like shown.I’ll take clearer pictures and we’ll check again tomorrow. The AC was working good so far. So I guess there must have wires somewhere.
Expert:  HVAC Guru replied 1 year ago.

Yes let me know when you locate them or if you still need help

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Expert:  BillyHvac replied 1 year ago.

Terrific,

just let me know and we will wrap up.

Just respond to "Billy"....and we can wrap this up.

Customer: replied 1 year ago.
It still doesn't work after changing all the connections. Please see the attached pictures before and after. I made a mistake by telling that there are 2 sets of wires coming from both thermostats to the furnace. Actually there is only one set. The other is coming from the outside AC. This AC set has 3 wires. White is connected to Com 24U, Red is connected to Y and the green is not connected. The 2 thermostats wires must be tied together somewhere in the wall because there is only 1 set going to the furnace. The cover of the wires at the thermostats are white. But at the furnace the cove is in chocolate color. I disconnected all the wires at the upstairs thermostat. When I turned the power back on, the new Honeywell thermostat screen is still blank. There must be no power coming in. Please let me know what's wrong?
Expert:  BillyHvac replied 1 year ago.

ok, the issue is where the wiring changes color. It is unlikely it is inside a wall...but could be tucked in a joist space.

So we 2 cables coming in..one from ac one from thermostats.......can you follow the wires at all before they go through floor or attic for the splice?

Expert:  HVAC Guru replied 1 year ago.

Just let me know if you have got it yet

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Customer: replied 1 year ago.
Billy,
The furnace is on the attic.The AC wire is going to outside AC. The thermostat wires disappears under wooden floor in the attic and I don't know where it's going. At the Honeywell thermostat there is terminal O/B. What is this for and what does it mean? If we cannot make it works, it's fine. I am going to return it and buy something more compatible. I still do not understand why the new thermostat had power and was running before and now it doesn't.
Expert:  BillyHvac replied 1 year ago.

The old thermostat did not need a common. The entire issue right now is if we had the same 5 wires run from the furnace to the thermostat we would be fine...but the 5 wires at furnace are not the wires at the thermostat we need.

Could the wiring be behind one of the thermostats? (splice)

Billy

Customer: replied 1 year ago.
Billy,
I mean the new Honeywell RTH 6500 Wi-Fi was lighting up and was working before when I made connections as follow:
W (white wire) to W2 terminal
G (green) to G
O (brown) to W
B (blue) to C
Y (yellow) to Y
R (red) to R & Rc (jumped)
I were able to control it from my smart phone. In this case I did not change any connection from the furnace. The connections at the furnace were as follow:
W (white wire) to W
Y to Y
R to R
G to G
B (blue) to red wire from the relay
O (brown) to green wire from the relay
At the furnace there is another set of 3 wires coming from the outside AC. The connection are:
White to COM 24U terminal
Red to Y terminal and Green is not being used (taped).Again it was working fine with this set-up . The problem was it worked only when I turned the existing White-Rodger thermostat upstairs ON. If I turned the switch to OFF the Honeywell went blank. The connections at this thermostat are:
W (white) to W
Y (yellow) to Y
R (red) to Rc & Rh (jumped). The rest of the wires are not connected.So I don't think there is an existing wiring issues of wirings behind the wall.
Customer: replied 1 year ago.
HVAC Guru,
No. It's not working yet. I am still working with Billy.
Quang
Expert:  BillyHvac replied 1 year ago.

at upper thermostat..twist the r and w wire together.

Then try lower thermostat

Customer: replied 1 year ago.
Do you mean after twisting the W and R together, I need to change everything back to the original settings as I just mentioned above?
Expert:  BillyHvac replied 1 year ago.

yes..but we still need blue to common

Customer: replied 1 year ago.
At the furnace, if I disconnected the B (blue wire) from the Red wire from the relay and connect it to COM terminal nothing is running. If I removed it from the COM and reconnected back to the Red wire from the relay the new Honeywell thermostat screen is on and I can control it from my phone. But then we are going back to the original problem. The furnace is running all the time even if I turned the Honeywell thermostat to OFF. Twisting the W and R wires from upstairs thermostat is the same as turn it ON. If I disconnect them then the Honeywell thermostat went blank and everything is OFF.
Expert:  BillyHvac replied 1 year ago.

wow...well this can be done...but we need to eliminate that relay and have the 5 wires that leave furnace terminals be the 5 wires that go to the thermostat (with no splicing).

I am afraid I will have to open this to the others if we cant get a dedicated 5 wire from furnace to thermostat

Customer: replied 1 year ago.
Could anyone out there solve my problem?

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